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What's the difference between <b> and <strong>, <i> and <em> in HTML/XHTML? When should you use each?
They have the same effect on normal web browser rendering engines, but there is a fundamental difference between them.
As the author writes in a discussion list post:
Think of three different situations:
web browsers
blind people
mobile phones
"Bold" is a style - when you say "bold a word", people basically know that
it means to add more, let's say "ink", around the letters until they stand out
more amongst the rest of the letters.
That, unfortunately, means nothing to a blind person. On mobile phones
and other PDAs, text is already bold because screen resolution is very small. You can't bold a bold without screwing something up.
<b> is a style - we know what "bold" is supposed to look like.
<strong> however is an indication of how something should be understood. "Strong" could (and often does) mean "bold" in a browser, but it could also mean a lower tone for a speaking program like Jaws (for blind people) or be represented by an underline (since you can't bold a bold) on a Palm Pilot.
HTML was never meant to be about styles. Do some searches for "Tim Berners-Lee" and "the semantic web." <strong> is semantic—it describes the text it surrounds (e.g., "this text should be stronger than the rest of the text you've displayed") as opposed to describing how the text it surrounds should be displayed (e.g., "this text should be bold").
<b> and <i> are explicit - they specify bold and italic respectively.
<strong> and <em> are semantic - they specify that the enclosed text should be "strong" or "emphasised" in some way, usually bold and italic, but allow for the actual styling to be controlled via CSS. Hence these are preferred in modern web pages.
<strong> and <em> add extra semantic meaning to your document. It just so happens that they also give a bold and italic style to your text.
You could of course override their styling with CSS.
<b> and <i> on the other hand only apply font styling and should no longer be used. (Because you're supposed to format with CSS, and if the text was actually important then you would probably make it "strong" or "emphasised" anyway!)
Hope that makes sense.
I'm going to hazard a historical and practical hot take here:
Yes, according to specifications, <strong> had a semantic meaning in HTML4 and <b> had a strictly presentational meaning.
Yes, when HTML5 came along, new semantic meaning that was slightly different was introduced for b and i.
Yes, the W3C recommends — basically — TL,DR; don't use b and i.
You should always bear in mind that the content of a b element may not always be bold, and that of an i element may not always be italic. The actual style is dependent on the CSS style definitions. You should also bear in mind that bold and italic may not be the preferred style for content in certain languages. You should not use b and i tags if there is a more descriptive and relevant tag available.
BUT:
The real world internet has massive loads of existing HTML that is never going to get updated. The real world internet has to account for content generated and copy and pasted between a vast network of software and CMS systems that all have different developer teams and were built in different eras.
So if you're writing HTML or building a system that writes HTML for other people — sure — definitely use <strong> instead of <b> to mean "strongly emphasized" because it's more semantically correct.
But really, the on-the-ground reality is that the semantic and stylistic meaning of <strong> and <b> have merged over time out of necessity.
If I'm building a CMS that allows any pasting of styled text, I need to plan both for people who are pasting in <b> and mean "strongly emphasized" and for people who are pasting in <strong> and mean "make this text bold". It might not be "right", but it's how the real world works at this moment in time.
And so, if I'm writing a stylesheet for that site, I'm probably going to end up writing some styles that look like this:
b,
strong {
font-weight: 700;
/* ... more styles here */
}
i,
em {
font-style: italic;
/* ... more styles here */
}
Or, I'm going to rely on the browser defaults, which do the same thing as the code above in every modern browser I know of.
Or, I might be one of probably millions of sites that use normalize.css, which takes care to ensure that b and strong are treated the same.
There's such a massive ocean of HTML out there in the world already that works off of this expectation, I just can't imagine that b will EVER be depreciated in favor of strong or that browsers will ever start displaying them differently by default.
So that's it. That's my hot take on semantics, history and the real world. Are b/i and strong/em the same? No. Will they probably both exist and be treated as identical in almost every situation until the collapse of modern civilization? I think, yes.
Here's a summary of definitions together with suggested usage:
<b> ...a span of text to which attention is being drawn for utilitarian purposes without conveying any extra importance and with no implication of an alternate voice or mood, such as key words in a document abstract, product names in a review, actionable words in interactive text-driven software, or an article lede.
<strong> ...now represents importance rather than strong emphasis.
<i> ...a span of text in an alternate voice or mood, or otherwise offset from the normal prose in a manner indicating a different quality of text, such as a taxonomic designation, a technical term, an idiomatic phrase from another language, a thought, or a ship name in Western texts.
<em> ...indicates emphasis.
(These are all direct quotes from W3C sources, with my emphasis added. See: https://rawgithub.com/whatwg/html-differences/master/Overview.html#changed-elements and http://www.w3.org/TR/html401/struct/text.html#h-9.2.1 for the originals)
<b> and <i> are both related to style, whereas <em> and <strong> are semantic. In HTML 4, the first are classified as font style elements, and the latter as phrase elements.
As you indicated correctly, <i> and <em> are often considered similar, because browsers often render both in italics. But according to the specifications, <em> indicates emphasis and <strong> indicates stronger emphasis, which is quite clear, but often misinterpreted. On the other hand, the distinction between when to use <i> or <b> is really a matter of style.
While <strong> and <em> are of course more semantically correct, there seem definite legitimate reasons to use the <b> and <i> tags for customer-written content.
In such content, words or phrases may be bolded or italicized and it is generally not up to us to analyze the semantic reasoning for such bolding or italicizing.
Further, such content may refer to bolded and italicized words and phrases to convey a specific meaning.
An example would be an english exam question which instructs a student to replace the bolded word.
<em> and <strong> consume more bandwidth than <i> and <b>.
They also require more typing (if not auto-generated).
They also clutter the editor screen with more text. I seem to recall that programmers like smaller source files if they are the same. (And let's be real, they are the same. Yes, there are "technical" (<i>cough</i>, ahem, excuse me) differences, but that's mostly phony to begin with.)
With any of the above tags, you can use style sheets to customize how they appear to however you want if you need them to appear different than their defaults renderings.
b or i means you want the text to be rendered as bold or italics. strong or em means you want the text to be rendered in a way that the user understands as "important". The default is to render strong as bold and em as italics, but some other cultures might use a different mapping.
Like strings in a program, b and i would be "hard coded" while strong and em would be "localized".
<i>, <b>, <em> and <strong> tags are traditionally representational. But they have been given new semantic meaning in HTML5.
<i> and <b> was used for font style in HTML4. <i> was used for italic and <b> for bold. In HTML5 <i> tag has new semantic meaning of 'alternate voice or mood' and <b> tag has the meaning of stylistically offset.
Example uses of <i> tag are - taxonomic designation, technical term, idiomatic phrase from another language, transliteration, a thought, ship names in western texts. Such as -
<p><i>I hope this works</i>, he thought.</p>
Example uses of <b> tag are keywords in a document extract, product names in a review, actionable words in an interactive text driven software, article lead.
The following example paragraph is stylistically offset from the paragraphs that follow it.
<p><b class="lead">The event takes place this upcoming Saturday, and over 3,000 people have already registered.</b></p>
<em> and <strong> had the meaning of emphasis and strong emphasis in HTML4. But in HTML5 <em> means stressed emphasis and <strong> means strong importance.
In the following example there should be a linguistic change while reading the word before ...
<p>Make sure to sign up <em>before</em> the day of the event, September 16, 2016</p>
In the same example we can use the <strong> tag as follows ..
<p>Make sure to sign up <em>before</em> the day of the event, <strong>September 16, 2016</strong></p>
to give importance on the event date.
MDN Ref:
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/b
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/i
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/em
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/strong
As others have said <b> and <i> are explicit (i.e. "make this text bold"), whereas <strong> and <em> are semantic (i.e. "this text should be emphasised").
In the context of a modern web-browser, it's difficult to see the difference (they both appear to produce the same result, right?), but think about screen readers for the visually impaired. If a screen-reader came across an <i> tag, it wouldn't know what to do. But if it comes across a <em> tag, it knows that whatever is within should be emphasised to the listener. And therein you get the practical difference.
As the others have stated, the difference is that <b> and <i> hardcode font styles, whereas <strong> and <em> dictate semantic meaning, with the font style (or speaking browser intonation, or what-have-you) to be determined at the time the text is rendered (or spoken).
You can think of this as a difference between a “physical” font style and a “logical” style, if you will. At some later time, you may wish to change the way <strong> and <em> text are displayed, say, by altering properties in a style sheet to add color and size changes, or even to use different font faces entirely. If you've used “logical” markup instead of hardcoded “physical” markup, then you can simply change the display properties in one place each in your style sheet, and then all of the pages that reference that style sheet get changed automatically, without ever having to edit them.
Pretty slick, huh?
This is also the rationale behind defining sub-styles (referenced using the style= property in text tags) for paragraphs, table cells, header text, captions, etc., and using <div> tags. You can define physical representation for your logical styles in the style sheet, and the changes are automatically reflected in the web pages that reference that style sheet. Want a different representation for source code? Redefine the font, size, weight, spacing, etc. for your "code" style.
If you use XHTML, you can even define your own semantic tags, and your style sheet would do the conversions to physical font styles and layouts for you.
I use both <strong> and <b>, actually, for exactly the reasons mentioned in this thread of responses. There are times when bold-facing some text simply looks better, but it isn't, necessarily, semantically more important than the rest of the sentence. Here's an example from a page I'm working on right now:
"Retrieves <strong>all</strong> books about <b>lacrosse</b>."
In that sentence, the word "all" is very important, and "lacrosse" less so--I merely wanted it bold because it represents a search term, so I wanted some visual separation. If you're viewing the page with a screen reader, I really don't think it needs to go out of the way to emphasize the word "lacrosse".
I would tend to imagine that most web developers use one of the other, but both are fine--<b> is most definitely not deprecated, as some people have claimed. For me, it's just a fine line between visual appeal and meaning.
Use them only if using CSS style classes is for any reason unconvinient or impossible (like blog systems, allow only some tags to use in posts and eventually embedded styles). Another reason is support for very old browsers (some mobile devices?) or primitive search engines (that give points for <b> or <strong> tags, instead of analysing CSS styles).
If you can define CSS styles, use them.
For text bold using <b> tag
For text important using <strong> tag
For text italic style using <i> tag
For emphasized text using <em> tag
<b> and <i>, having no actual semantic meaning (like #splattne pointed out) was true, a long time ago. In modern HTML5 (<!DOCTYPE html>) they do have meaning. Check out the following links.
Semantic meaning (from MDN)
<b>: Bring Attention To element
Keywords in a summary
product names.
<p>Here at company XYZ, we use <b>HTML</b> and <b>Javascript</b>.</p>
<i>: Idiomatic Text element
Alternative voice or mood
Taxonomic designations (such as the genus and species "Homo sapiens")
Idiomatic terms from another language (such as "et cetera")
Technical terms
<p>I <i>did</i> tell him, to arrive on time for the meeting.</p>
<b> vs. <strong>
It may help to realize that both are valid and semantic elements in HTML5 and that it's a coincidence that they both have the same default styling (boldface) in most browsers (although some older browsers actually underline <strong>). Each element is meant to be used in certain types of scenarios, and if you want to bold text for decoration, you should instead actually use the CSS font-weight property. source
<i> vs. <em>
The <em> element represents stress emphasis of its contents, while the <i> element represents text that is set off from the normal prose. source
My 2 cents
I personaly prefer <b> and <i> over <strong> and <em>.
They are shorter, and their semantic meaning just makes sense, from a developer point of view too.
I have no idea if todays screen readers can work with them. If not, I think they will eventually. A18n is a difficult topic, I just follow the lead of documentation. MDN says I can use them, so I do.
Q: Difference between strong, b, bold, em, i?
Ans: These are inline properties.
Strong: It is used to show text bold or highlight it semantically.
Bold or b: This bold tag is just offset text conventionally styled in bold.
em: <em> tag semantically emphasizes the important word.
i : <i> tag just offset text conventionally styled in italic.
note: you should use <strong></strong> and <em></em> tags their meaningful names which tell about the type of content. Semantic tags are also helpful for SEO.
<b> and <i> should be avoided because they describe the style of the text. Instead, use <strong> and <em> because that describes the semantics (the meaning) of the text.
As with all things in HTML, you should be thinking not about how you want it to look, but what you actually mean. Sure, it might just be bold and italics to you, but not to a screen reader.
"They have the same effect. However, XHTML, a cleaner, newer version of HTML, recommends the use of the <strong> tag. Strong is better because it is easier to read - its meaning is clearer. Additionally, <strong> conveys a meaning - showing the text strongly - while <b> (for bold) conveys a method - bolding the text. With strong, your code still makes sense if you use CSS stylesheets to change what the methods of making the text strong is.
The same goes for the difference between <i> and <em> ".
Google dixit:
http://wiki.answers.com/Q/What_is_the_difference_between_HTML_tags_b_and_strong
HTML Formatting Elements:
HTML also defines special elements for defining text with a special meaning.
HTML uses elements like <b> and <i> for formatting output, like bold or italic text.
HTML Bold and Strong Formatting:
The HTML <b> element defines bold text, without any extra importance.
<b>This text is bold</b>
The HTML <strong> element defines strong text, with added semantic
"strong" importance.
<strong>This text is strong</strong>
HTML Italic and Emphasized Formatting:
The HTML <i> element defines italic text, without any extra
importance.
<i>This text is italic</i>
The HTML <em> element defines emphasized text, with added semantic
importance.
<em>This text is emphasized</em>
You should generally try to avoid <b> and <i>. They were introduced for layouting the page (changing the way how it looks) in early HMTL versions prior to the creation of CSS, like the meanwhile removed font tag, and were mainly kept for backward compatibility and because some forums allow inline HTML and that's an easy way to change the look of text (like BBCode using [i], you can use <i> and so on).
Since the creation of CSS, layouting is actually nothing that should be done in HTML anymore, that's why CSS has been created in the first place (HTML == Structure, CSS == Layout). These tags may as well vanish in the future, after all you can just use CSS and span tags to make text bold/italic if you need a "meaningless" font variation. HTML 5 still allows them but declares that marking text that way has no meaning.
<em> and <strong> on the other hand only says that something is "emphasized" or "strongly emphasized", it leaves it completely open to the browser how to render it. Most browsers will render em as italic and strong as bold as the standard suggests by default, but they are not forced to do that (they may use different colors, font sizes, fonts, whatever). You can use CSS to change the behavior the way you desire. You can make em bold if you like and strong bold and red, for example.
<strong> and <em> are abstract (which is what people mean when they say it's semantic).
<b> and <i> are specific ways of making something "strong" or "emphasized"
Analogy:
Both <strong> is to <b> and <em> is to <i>
as
"vehicle" is to "jeep"
In HTML Lang, these two tags are used as follows:
simple text this is test text normal text
simple text this is important textwith normal text
The major diversity between these two HTML tags is that bold makes text only visually look bold, while strong also symbolism hit the respective text as essential and indicates that it is a clear word or text section.
This difference is due to the fact that HTML code differentiates between symbolism and physical visual html tags. While the earlier refer to the meaning of the relevant areas, the latter merely define the optical display in browsers.
We use the <strong> tag for text which has high priority for SEO purposes like product name, company name etc, while <b> simple makes it bold.
Similarly, we use <em> for text which has high priority for SEO, while <i> to make the text simply italic.
I've always used <b> tag to bold something, because that is the way I was taught to do it a long time ago. But now my IDE always informs me that <b> is deprecated and to use css style. Assuming by that they want me to use <div style="font-weight:bold;">Bold Text</div>. How vital is this message that my IDE is giving me? Should I go back and change all my<b> to style?
Below is an example of both situations. Could someone explain the difference's between both and why <b> is deprecated now?
<b>Bold Text</b>
Vs.
<div style="font-weight:bold;">Bold Text</div>
Would <b> be better because if someone has css turned off on the browser, it would still be show correctly?
The correct question is: "What markup best describes my content?"
Let's start with the <b> tag (which is not deprecated):
The b element represents a span of text to be stylistically offset
from the normal prose without conveying any extra importance, such as
key words in a document abstract, product names in a review, or other
spans of text whose typical typographic presentation is boldened.
...
You should not use b and i tags if there is a more descriptive and
relevant tag available. If you do use them, it is usually better to
add class attributes that describe the intended meaning of the markup,
so that you can distinguish one use from another.
...
It may help to think of b or i elements as essentially a span element
with an automatic fallback styling. Just like a span element, these
elements usually benefit from class names if they are to be useful.
http://www.w3.org/International/questions/qa-b-and-i-tags
By comparison, <strong> has a more specific purpose:
The strong element represents a span of text with strong importance.
http://www.w3.org/TR/html-markup/strong.html
For example:
<p><strong>Warning.</strong> Here be dragons.</p>
Here we emphasize the word "warning" to stress its importance.
But not:
<p><strong>Item 1:</strong> Foo, bar, and baz.</p>
"Item 1" isn't meant to be stressed, so <strong> is the wrong tag. Furthermore, it's possible that the whole structure could be better represented.
If the meaning of the text has strong importance, <strong> is appropriate (just like this line).
Perhaps you just want a thicker font for style purposes and the text has no particular meaning. In that case, neither <strong> nor <b> may be appropriate.
<span class="product-name">Hello World</span>
.product-name { font-weight: bold; }
In all cases:
Use the markup which describes the content.
Do not use inline styles (use an external stylesheet).
Do not name styles based on their visual representation (e.g. naming a style "bold" is a poor choice)
Would <b> be better because if someone has css turned off on the
browser, it would still be show correctly?
No. Use the correct markup for the job. It's fairly unusual for someone using the visual representation of your site to willingly disable the stylesheet, but non-visual consumers care primarily about the structure of your document. A "non-visual consumer" could be a search engine parsing your content or a screen reader application.
Additional Reading:
http://www.w3.org/TR/html51/text-level-semantics.html#the-strong-element
http://www.w3.org/TR/html51/text-level-semantics.html#the-b-element
It's not "vital" if the code still works. Though it would conform to current standards which will give the code a longer future.
The difference is that using CSS separates your styling from your content. <b> is a style, nothing more. And it tightly couples that markup to that style. The separation allows you to emphasize the markup in other ways instead of always using a bold font.
Would be better because if someone has css turned off on the browser, it would still be show correctly?
No, because if the user wants to disable styling then your <b> tag undermines that, because it's mixing styling with content.
You should be using <strong> in place of <b>. You could use styles (text-weight: bold in a separate sheet) if a particular group of text was always going to be bold, and you didn't (or couldn't) want to use <strong> for whatever reason. But I would only go that route if you already were applying other styles to that same element.
If you are talking about SEO
Use <strong> should be SEO friendly too... (focus on the keywords)
and it's important !
I find that using <strong></strong> is the better approach than using <b> or inline styles.
Sorry if this is sounding fussy but I'm about to produce a whole lot of HTML 5 and I was hoping someone out there had come up with some clear rules for when to use the <em>, <strong> and <mark> tags. The spec suggests some subtle differences but I keep finding myself asking whether I want the text bolded, italic or yellow high-lighted, which makes me think I should be using CSS instead. (And sometimes I wonder why I even bother when I could just as easily write "Cats are NOT dogs.")
I keep finding myself asking whether I want the text bolded, italic or yellow high-lighted, which makes me think I should be using CSS instead.
That's 100% correct. Markup is for describing content, not appearance. That being said:
http://www.w3.org/html/wg/drafts/html/master/text-level-semantics.html
The <strong> element represents strong importance for its contents. Changing the importance of a piece of text with the strong element does not change the meaning of the sentence.
The <em> element represents stress emphasis of its contents. The placement of stress emphasis changes the meaning of the sentence.
The <mark> element represents a run of text in one document marked or highlighted for reference purposes, due to its relevance in another context.
<mark> doesn't really have relevance to content, only context (e.g. marking content that matches a search term, misspelled words, selected content in a web app, etc.).
<strong> denotes important text, but does not affect meaning.
<em> denotes important text and affects the meaning of the content by saying that it should be read/spoken with emphasis.
You are free to use CSS to change browser defaults for all of these elements.
Remember HTML is a markup language. Inside it you write the content of the page. If you use "Cats are NOT dogs", search engines like google don't know whether "DOGS" is a distinguished phrase or not (of course your readers will notice it, though). If you use CSS, which is a styling language, same thing happens: search engines don't recognize "DOGS" as distinguished text but users do.
When you use the elements of your question, they indeed give information. They're called semantic elements. For example it's more informative for the search engine (or screen reader or speaking software) to use element <h1> for titles than just using <p> and through CSS making it big and bold. Another example is using alt and title attributes in img, 'cause engines don't understand what image you have in src.
So, even though any of the HTML elements <em>, <strong>, <mark> are noticeable for the user, they give different meaning to the text inside them for the engines.
Look for writing style for e.g. books. True, webpages are less formal than this, but it should give you a starting point. Italic text (i.e., <em>) is used for emphasis. Boldface (<strong>) is used for titles and such, very rarely in running text.
What's the difference between <b> and <strong>, <i> and <em> in HTML/XHTML? When should you use each?
They have the same effect on normal web browser rendering engines, but there is a fundamental difference between them.
As the author writes in a discussion list post:
Think of three different situations:
web browsers
blind people
mobile phones
"Bold" is a style - when you say "bold a word", people basically know that
it means to add more, let's say "ink", around the letters until they stand out
more amongst the rest of the letters.
That, unfortunately, means nothing to a blind person. On mobile phones
and other PDAs, text is already bold because screen resolution is very small. You can't bold a bold without screwing something up.
<b> is a style - we know what "bold" is supposed to look like.
<strong> however is an indication of how something should be understood. "Strong" could (and often does) mean "bold" in a browser, but it could also mean a lower tone for a speaking program like Jaws (for blind people) or be represented by an underline (since you can't bold a bold) on a Palm Pilot.
HTML was never meant to be about styles. Do some searches for "Tim Berners-Lee" and "the semantic web." <strong> is semantic—it describes the text it surrounds (e.g., "this text should be stronger than the rest of the text you've displayed") as opposed to describing how the text it surrounds should be displayed (e.g., "this text should be bold").
<b> and <i> are explicit - they specify bold and italic respectively.
<strong> and <em> are semantic - they specify that the enclosed text should be "strong" or "emphasised" in some way, usually bold and italic, but allow for the actual styling to be controlled via CSS. Hence these are preferred in modern web pages.
<strong> and <em> add extra semantic meaning to your document. It just so happens that they also give a bold and italic style to your text.
You could of course override their styling with CSS.
<b> and <i> on the other hand only apply font styling and should no longer be used. (Because you're supposed to format with CSS, and if the text was actually important then you would probably make it "strong" or "emphasised" anyway!)
Hope that makes sense.
I'm going to hazard a historical and practical hot take here:
Yes, according to specifications, <strong> had a semantic meaning in HTML4 and <b> had a strictly presentational meaning.
Yes, when HTML5 came along, new semantic meaning that was slightly different was introduced for b and i.
Yes, the W3C recommends — basically — TL,DR; don't use b and i.
You should always bear in mind that the content of a b element may not always be bold, and that of an i element may not always be italic. The actual style is dependent on the CSS style definitions. You should also bear in mind that bold and italic may not be the preferred style for content in certain languages. You should not use b and i tags if there is a more descriptive and relevant tag available.
BUT:
The real world internet has massive loads of existing HTML that is never going to get updated. The real world internet has to account for content generated and copy and pasted between a vast network of software and CMS systems that all have different developer teams and were built in different eras.
So if you're writing HTML or building a system that writes HTML for other people — sure — definitely use <strong> instead of <b> to mean "strongly emphasized" because it's more semantically correct.
But really, the on-the-ground reality is that the semantic and stylistic meaning of <strong> and <b> have merged over time out of necessity.
If I'm building a CMS that allows any pasting of styled text, I need to plan both for people who are pasting in <b> and mean "strongly emphasized" and for people who are pasting in <strong> and mean "make this text bold". It might not be "right", but it's how the real world works at this moment in time.
And so, if I'm writing a stylesheet for that site, I'm probably going to end up writing some styles that look like this:
b,
strong {
font-weight: 700;
/* ... more styles here */
}
i,
em {
font-style: italic;
/* ... more styles here */
}
Or, I'm going to rely on the browser defaults, which do the same thing as the code above in every modern browser I know of.
Or, I might be one of probably millions of sites that use normalize.css, which takes care to ensure that b and strong are treated the same.
There's such a massive ocean of HTML out there in the world already that works off of this expectation, I just can't imagine that b will EVER be depreciated in favor of strong or that browsers will ever start displaying them differently by default.
So that's it. That's my hot take on semantics, history and the real world. Are b/i and strong/em the same? No. Will they probably both exist and be treated as identical in almost every situation until the collapse of modern civilization? I think, yes.
Here's a summary of definitions together with suggested usage:
<b> ...a span of text to which attention is being drawn for utilitarian purposes without conveying any extra importance and with no implication of an alternate voice or mood, such as key words in a document abstract, product names in a review, actionable words in interactive text-driven software, or an article lede.
<strong> ...now represents importance rather than strong emphasis.
<i> ...a span of text in an alternate voice or mood, or otherwise offset from the normal prose in a manner indicating a different quality of text, such as a taxonomic designation, a technical term, an idiomatic phrase from another language, a thought, or a ship name in Western texts.
<em> ...indicates emphasis.
(These are all direct quotes from W3C sources, with my emphasis added. See: https://rawgithub.com/whatwg/html-differences/master/Overview.html#changed-elements and http://www.w3.org/TR/html401/struct/text.html#h-9.2.1 for the originals)
<b> and <i> are both related to style, whereas <em> and <strong> are semantic. In HTML 4, the first are classified as font style elements, and the latter as phrase elements.
As you indicated correctly, <i> and <em> are often considered similar, because browsers often render both in italics. But according to the specifications, <em> indicates emphasis and <strong> indicates stronger emphasis, which is quite clear, but often misinterpreted. On the other hand, the distinction between when to use <i> or <b> is really a matter of style.
While <strong> and <em> are of course more semantically correct, there seem definite legitimate reasons to use the <b> and <i> tags for customer-written content.
In such content, words or phrases may be bolded or italicized and it is generally not up to us to analyze the semantic reasoning for such bolding or italicizing.
Further, such content may refer to bolded and italicized words and phrases to convey a specific meaning.
An example would be an english exam question which instructs a student to replace the bolded word.
<em> and <strong> consume more bandwidth than <i> and <b>.
They also require more typing (if not auto-generated).
They also clutter the editor screen with more text. I seem to recall that programmers like smaller source files if they are the same. (And let's be real, they are the same. Yes, there are "technical" (<i>cough</i>, ahem, excuse me) differences, but that's mostly phony to begin with.)
With any of the above tags, you can use style sheets to customize how they appear to however you want if you need them to appear different than their defaults renderings.
b or i means you want the text to be rendered as bold or italics. strong or em means you want the text to be rendered in a way that the user understands as "important". The default is to render strong as bold and em as italics, but some other cultures might use a different mapping.
Like strings in a program, b and i would be "hard coded" while strong and em would be "localized".
<i>, <b>, <em> and <strong> tags are traditionally representational. But they have been given new semantic meaning in HTML5.
<i> and <b> was used for font style in HTML4. <i> was used for italic and <b> for bold. In HTML5 <i> tag has new semantic meaning of 'alternate voice or mood' and <b> tag has the meaning of stylistically offset.
Example uses of <i> tag are - taxonomic designation, technical term, idiomatic phrase from another language, transliteration, a thought, ship names in western texts. Such as -
<p><i>I hope this works</i>, he thought.</p>
Example uses of <b> tag are keywords in a document extract, product names in a review, actionable words in an interactive text driven software, article lead.
The following example paragraph is stylistically offset from the paragraphs that follow it.
<p><b class="lead">The event takes place this upcoming Saturday, and over 3,000 people have already registered.</b></p>
<em> and <strong> had the meaning of emphasis and strong emphasis in HTML4. But in HTML5 <em> means stressed emphasis and <strong> means strong importance.
In the following example there should be a linguistic change while reading the word before ...
<p>Make sure to sign up <em>before</em> the day of the event, September 16, 2016</p>
In the same example we can use the <strong> tag as follows ..
<p>Make sure to sign up <em>before</em> the day of the event, <strong>September 16, 2016</strong></p>
to give importance on the event date.
MDN Ref:
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/b
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/i
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/em
https://developer.mozilla.org/en-US/docs/Web/HTML/Element/strong
As others have said <b> and <i> are explicit (i.e. "make this text bold"), whereas <strong> and <em> are semantic (i.e. "this text should be emphasised").
In the context of a modern web-browser, it's difficult to see the difference (they both appear to produce the same result, right?), but think about screen readers for the visually impaired. If a screen-reader came across an <i> tag, it wouldn't know what to do. But if it comes across a <em> tag, it knows that whatever is within should be emphasised to the listener. And therein you get the practical difference.
As the others have stated, the difference is that <b> and <i> hardcode font styles, whereas <strong> and <em> dictate semantic meaning, with the font style (or speaking browser intonation, or what-have-you) to be determined at the time the text is rendered (or spoken).
You can think of this as a difference between a “physical” font style and a “logical” style, if you will. At some later time, you may wish to change the way <strong> and <em> text are displayed, say, by altering properties in a style sheet to add color and size changes, or even to use different font faces entirely. If you've used “logical” markup instead of hardcoded “physical” markup, then you can simply change the display properties in one place each in your style sheet, and then all of the pages that reference that style sheet get changed automatically, without ever having to edit them.
Pretty slick, huh?
This is also the rationale behind defining sub-styles (referenced using the style= property in text tags) for paragraphs, table cells, header text, captions, etc., and using <div> tags. You can define physical representation for your logical styles in the style sheet, and the changes are automatically reflected in the web pages that reference that style sheet. Want a different representation for source code? Redefine the font, size, weight, spacing, etc. for your "code" style.
If you use XHTML, you can even define your own semantic tags, and your style sheet would do the conversions to physical font styles and layouts for you.
I use both <strong> and <b>, actually, for exactly the reasons mentioned in this thread of responses. There are times when bold-facing some text simply looks better, but it isn't, necessarily, semantically more important than the rest of the sentence. Here's an example from a page I'm working on right now:
"Retrieves <strong>all</strong> books about <b>lacrosse</b>."
In that sentence, the word "all" is very important, and "lacrosse" less so--I merely wanted it bold because it represents a search term, so I wanted some visual separation. If you're viewing the page with a screen reader, I really don't think it needs to go out of the way to emphasize the word "lacrosse".
I would tend to imagine that most web developers use one of the other, but both are fine--<b> is most definitely not deprecated, as some people have claimed. For me, it's just a fine line between visual appeal and meaning.
Use them only if using CSS style classes is for any reason unconvinient or impossible (like blog systems, allow only some tags to use in posts and eventually embedded styles). Another reason is support for very old browsers (some mobile devices?) or primitive search engines (that give points for <b> or <strong> tags, instead of analysing CSS styles).
If you can define CSS styles, use them.
For text bold using <b> tag
For text important using <strong> tag
For text italic style using <i> tag
For emphasized text using <em> tag
<b> and <i>, having no actual semantic meaning (like #splattne pointed out) was true, a long time ago. In modern HTML5 (<!DOCTYPE html>) they do have meaning. Check out the following links.
Semantic meaning (from MDN)
<b>: Bring Attention To element
Keywords in a summary
product names.
<p>Here at company XYZ, we use <b>HTML</b> and <b>Javascript</b>.</p>
<i>: Idiomatic Text element
Alternative voice or mood
Taxonomic designations (such as the genus and species "Homo sapiens")
Idiomatic terms from another language (such as "et cetera")
Technical terms
<p>I <i>did</i> tell him, to arrive on time for the meeting.</p>
<b> vs. <strong>
It may help to realize that both are valid and semantic elements in HTML5 and that it's a coincidence that they both have the same default styling (boldface) in most browsers (although some older browsers actually underline <strong>). Each element is meant to be used in certain types of scenarios, and if you want to bold text for decoration, you should instead actually use the CSS font-weight property. source
<i> vs. <em>
The <em> element represents stress emphasis of its contents, while the <i> element represents text that is set off from the normal prose. source
My 2 cents
I personaly prefer <b> and <i> over <strong> and <em>.
They are shorter, and their semantic meaning just makes sense, from a developer point of view too.
I have no idea if todays screen readers can work with them. If not, I think they will eventually. A18n is a difficult topic, I just follow the lead of documentation. MDN says I can use them, so I do.
Q: Difference between strong, b, bold, em, i?
Ans: These are inline properties.
Strong: It is used to show text bold or highlight it semantically.
Bold or b: This bold tag is just offset text conventionally styled in bold.
em: <em> tag semantically emphasizes the important word.
i : <i> tag just offset text conventionally styled in italic.
note: you should use <strong></strong> and <em></em> tags their meaningful names which tell about the type of content. Semantic tags are also helpful for SEO.
<b> and <i> should be avoided because they describe the style of the text. Instead, use <strong> and <em> because that describes the semantics (the meaning) of the text.
As with all things in HTML, you should be thinking not about how you want it to look, but what you actually mean. Sure, it might just be bold and italics to you, but not to a screen reader.
"They have the same effect. However, XHTML, a cleaner, newer version of HTML, recommends the use of the <strong> tag. Strong is better because it is easier to read - its meaning is clearer. Additionally, <strong> conveys a meaning - showing the text strongly - while <b> (for bold) conveys a method - bolding the text. With strong, your code still makes sense if you use CSS stylesheets to change what the methods of making the text strong is.
The same goes for the difference between <i> and <em> ".
Google dixit:
http://wiki.answers.com/Q/What_is_the_difference_between_HTML_tags_b_and_strong
HTML Formatting Elements:
HTML also defines special elements for defining text with a special meaning.
HTML uses elements like <b> and <i> for formatting output, like bold or italic text.
HTML Bold and Strong Formatting:
The HTML <b> element defines bold text, without any extra importance.
<b>This text is bold</b>
The HTML <strong> element defines strong text, with added semantic
"strong" importance.
<strong>This text is strong</strong>
HTML Italic and Emphasized Formatting:
The HTML <i> element defines italic text, without any extra
importance.
<i>This text is italic</i>
The HTML <em> element defines emphasized text, with added semantic
importance.
<em>This text is emphasized</em>
You should generally try to avoid <b> and <i>. They were introduced for layouting the page (changing the way how it looks) in early HMTL versions prior to the creation of CSS, like the meanwhile removed font tag, and were mainly kept for backward compatibility and because some forums allow inline HTML and that's an easy way to change the look of text (like BBCode using [i], you can use <i> and so on).
Since the creation of CSS, layouting is actually nothing that should be done in HTML anymore, that's why CSS has been created in the first place (HTML == Structure, CSS == Layout). These tags may as well vanish in the future, after all you can just use CSS and span tags to make text bold/italic if you need a "meaningless" font variation. HTML 5 still allows them but declares that marking text that way has no meaning.
<em> and <strong> on the other hand only says that something is "emphasized" or "strongly emphasized", it leaves it completely open to the browser how to render it. Most browsers will render em as italic and strong as bold as the standard suggests by default, but they are not forced to do that (they may use different colors, font sizes, fonts, whatever). You can use CSS to change the behavior the way you desire. You can make em bold if you like and strong bold and red, for example.
<strong> and <em> are abstract (which is what people mean when they say it's semantic).
<b> and <i> are specific ways of making something "strong" or "emphasized"
Analogy:
Both <strong> is to <b> and <em> is to <i>
as
"vehicle" is to "jeep"
In HTML Lang, these two tags are used as follows:
simple text this is test text normal text
simple text this is important textwith normal text
The major diversity between these two HTML tags is that bold makes text only visually look bold, while strong also symbolism hit the respective text as essential and indicates that it is a clear word or text section.
This difference is due to the fact that HTML code differentiates between symbolism and physical visual html tags. While the earlier refer to the meaning of the relevant areas, the latter merely define the optical display in browsers.
We use the <strong> tag for text which has high priority for SEO purposes like product name, company name etc, while <b> simple makes it bold.
Similarly, we use <em> for text which has high priority for SEO, while <i> to make the text simply italic.
Well I know it's not evil just not as pretty in semantics as <strong> and <em> right?
However, with <b> becoming more semantic as <strong> and <i> as <em>, why isn't there a semantic twin for <u>?
In styling:
So there's a CSS style text-decoration:underline for <u>, but isn't there one font-weight:bold for <strong> already? Thus goes <em> too.
In semantics:
<strong> is semantic for what? Strongly emphasized text?
<em> is semantic for what? Emphasized text?
Anything fundamentally different from each other and mutually exclusive? No.
Why can't there be another way to emphasize text? You know, like the way <u> does and makes up a semantic twin for it too - I guess it's just <strong> and <em> are already well implemented in all major browsers before the <b> and <i> become obselete.
I know, now that it's officially become standards, you just have to go with it. Or please have your say: is there a compelling reason to make <u> out of view?
If a semantic twin was created for every previously existing styling tag, all we'd be doing is the same old thing, albeit with new names.
<strong> and <em> are used to give meaning to the marked up text. Their default styling corresponds to <b> and <i> because that's how most people display strength and emphasis in print -- But that can be changed. Whereas using CSS to change a <b> may seem counter intuitive.
So the direct answer to your question is: <strong> and <em> impart meaning to the text, whereas <u> and the others impart styling to the text, which is now done by CSS. The styling applied by the others is incidental.
It gets mistaken for a hyperlink.
font-weight:bold is not equivalent to strong. The strong tag has that attribute by default, but you're free to make it underline or turn red or anything else you like. That's the point: It does not specify styling.
<strong> is semantic for what? Strongly emphasized text? <em> is semantic for what?
‘Emphasis’ and ‘strong emphasis’ are not well-defined, so the semantic content is quite low.
You can come up with your own interpretation: for example, I personally use:
<em> is for parts of a sentence that would be stressed when spoken out loud
<strong> is for stretches of text that need to be visually picked out: for example particularly important sentences, and visual scanning keywords.
This is consistent and to some extent matches typical use, but it is not mandated by HTML.
and <i> as <em>
<em> is not a 1:1 fit with italics even disregarding the styling issue. There are other reasons for using italics, including:
<cite>ing other works, according to HTML 4.01 Specification
picking out phrases from other languages to the main text, which is <span lang="fr">'s raison d'être
why isn't there a semantic twin for <u>
Because everyone hates <u>.
Even in HTML2 days it was rarely used, because it's so ugly.
Underlining is a leftover from the age of the typewriter. At that time there was no option for neither italic nor bold, so the only way to emphasize words was to use underline. The nice thing about underline (from a typewriter designer point of view) is that you can modify existing characters, so you don't need to have an entire set of extra characters.
It is not beautiful and there is no longer any need for it, so please use italic or bold instead.
The problem is only more pronounced as underlining is the standard decoration for links in HTML.
In styling:
So there's a CSS style
text-decoration:underline for <u>, but
isn't there one font-weight:bold for
<strong> already? Thus goes <em> too.
No. There isn't a CSS style for <strong> or <em>. There are CSS tags for bold, but that is not the same thing. strong and em do not mean bold. They mean emphasize. Emphasize can be done with underlining, with italic or with bold in a textual media, and it's up to the stylesheet to decide which. But the semantic meaning is simply "this text is emphasized". And how would you implement "underline" in a screen reader? It doesn't make sense. underline is specific to textual media, and thus belongs in the specific stylesheet for textual presentation, and not in the semantic HTML which could be used to present data through speech or any other media.
In semantics:
<strong> is semantic for what?
Strongly emphasized text? <em> is
semantic for what? Emphasized text?
Anything fundamentally different from
each other and mutually exclusive? No.
Why can't there be another way to
emphasize text? You know, like the way
<u> does
Because strong and em do not specify how the text should be emphasized, just that it should be emphasized. underline specifies how it should be emphasized, thus it has to do with presentation, rather than semantics, and belongs in a CSS file.
I agree that the difference between strong and em is vague, but then again, we also have h1-h7. The point is that even without a stylesheet, a reader should be able to infer that "this is bigger headline than that", and so also "this text is more emphasized than that".
The semantic meaning of tags do not have to be fundamentally different from each others. It's perfectly meaningful to have semantic tags that simply mean "more so than this other semantic tag". Because sometimes we have a need for several layers of headlines in our text, so we have h1-h7. And sometimes we have a need for text that is emphasized, and text that is very emphasized. But even if we didn't, it still wouldn't be an excuse for adding <u> as "another semantic twin", because it isn't. It's not a semantic twin, it is nothing in semantics. underline does not necessarily mean emphasis. It could mean headline as well, or it could mean "this is a link", or it could mean anything else you want it to mean. It is a presentation detail. And it is meaningless in a non-text media. "emphasis" is not a presentation detail. It carries a semantic meaning which makes sense no matter the media. You can emphasize information in movies too, or in video games, or in text read aloud.
You seem to be under the impression that strong and em are just shorthand (or longhand) for bold or italic. That's not true. They may be used to present bold text, underlined text, or italic text, or larger text. Or they can be ignored completely. Or they may simply alter the pronunciation in a screen reader. If you've ever written documents in LaTeX, you'll note that the \emph command there is typically rendered as italic, not bold. Of course it's not required to, but that's a perfectly legal interpretation of the semantic "emphasis" command. Similarly, there are many other tags which may just end up rendered as italic (quotes, or span tags with certain CSS classes or even headlines.
<u>, on the other hand, has a very specific meaning in presentation, but carries no semantic value. What information does it convey to the reader? <strong> carries the meaning "this text is highlighed and should be paid attention to", because it is strongly emphasized. What does it mean for text to be underlined? It could mean nothing, or it could mean a dozen different things.
"italic", "bold" or "underline" are presentational attributes with no semantic meaning. They can be applied to any semantic HTML tag you like. And semantic tags like strong or em can use any presentational CSS rules you like. There is no 1:1 mapping as you seem to believe. They are different concepts. The fact that the browser by default chooses to render strong text as bold is completely irrelevant. That's just a default behavior, because they had to choose something, and it can be overridden in CSS.
It's not a question of "can this be done in CSS", or "Is this a semantic twin of that", but simply "does it have a semantic meaning? Does it have a presentational meaning"? If yes to both, it should be changed and/or removed entirely. If yes to the former, it belongs in HTML, and if yes to the latter it belongs in CSS.
The semantic twin of <u> is <a>. ^_^ This is a bit facetious, but it's true. On the web, underlined text denotes a link by default; this pattern is so old and well-established that nearly every single (sighted) person on the web has automatically interned it as part of how they interact with a page.
HTML5 defines slightly different meanings for <em> and <strong>, specifically so you don't just have two tags that both do the same thing semantically. That just invites questions like yours, where you wonder why there isn't just a third way to emphasize something with an underlined presentation (or what-have-you) by default.
In HTML5, <em> still denotes emphasis. Using an <em> changes the meaning of a sentence by putting a focus on particular words or phrases. <strong>, on the other hand, denotes importance. Marking a word or phrase as important does not change the meaning of the sentence, it merely directs your attention.
As usual, the standard caveats about <em> being rendered with italics by default and <strong> being rendered with bold text by default, but it being perfectly possible and appropriate to change the presentation of either, applies. For example, a screen reader may use different inflections for the two tags. This is the whole reason that semantics exist - so that we can allow the presenter to decide the best way to present the data; us mortal authors can't possibly get the presentation correct in every possible medium.
To a typographer, underlining and bold are two ways to make something strong. Most people believe underline is uglier than bold text, and it is therefore normally reserved for when bold isn't available - e.g. on a typewriter, or when hand-writing something, or marking something up with a pencil.
If you really want underlining, it's perfectly valid to do:
<style>
strong {
font-weight: normal;
text-decoration: underline;
}
</style>
The web just doesn't lend itself to underlined text. I agree with Greg that it could easily be confused with a link.
it is not semantic. we live in a world of increasing importance of semantics in our code, because we are sick of trying to decipher some other coders "it makes sense to me" mess.
Underlining is ugly, be it in books or on the web. So it should only be used for emphasis in handwritten text, where there is no alternative.