What is the impact of <i>, <b>, <strong> or <span> elements on SEO?

Question

What is the impact of i, b, strongor span tags on SEO?

I quote the MDN HTML element reference:

The HTML <b> Element represents a span of text stylistically different from normal text, without conveying any special importance or relevance. It is typically used for keywords in a summary, product names in a review, or other spans of text whose typical presentation would be boldfaced. Another example of its use is to mark the lead sentence of each paragraph of an article.

The HTML <i> Element represents a range of text that is set off from the normal text for some reason, for example, technical terms, foreign language phrases, or fictional character thoughts. It is typically displayed in italic type.

The HTML Strong Element (<strong>) gives text strong importance, and is typically displayed in bold.

From these, the three of them could be used to highlight "important text". But I don't really know what would be the impact on the semantics, from a SEO perspective.

Until now, I was mostly using the span tag with styling attribute in order to raise visual importance to important words without polluting the code with visual style items.

However, those important words, are indeed important. I mean that it could be smart to highlight them from a SEO perspective. span being meaningless, switching to another tag may be a good idea after all.

Do you know if there are any differences between those three alternative tags to optimize search engine results?

Answer 1

The impact of those styling tags (itself) is very big near nothing.

Ok, why is this exactly not what it seems to be?

Several sources are talking about the impact of CSS styling, the impact of responsiveness (See links at question), and the impact of semanticity and saying usually completely different things.
(Not least because they are created at different times)

One is:

There are no measured differences between using span with CSS-Stylings and using i or b.

With accessibility out of mind, this is a fact. At this time, b is - like span - just a styling tag.

Another one:

There is no difference between using b and using <strong>, <em>, or <mark>.

This is wrong. While b makes text bold, strong represents important text. (Also without being bold)

For an explanation, see the reference for <b>:

Do not confuse the <b> element with the <strong>, <em>, or <mark> elements. The <strong> element represents text of certain importance, <em> puts some emphasis on the text and the <mark> element represents text of certain relevance. The <b> element doesn't convey such special semantic information; use it only when no others fit.

This is good for screen readers, crawlers, and (search) engines.
And as we already know:

Good things rank good.

The general most accurate statement is that Search Engines rank your pages based on the quality of your content.

If your decision to use <span> or <strong>, <em>, and <mark> is based on the impact for your Page Rank, then definitely no, it wont help you.

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To say it with a little of my opinion:

If you write good content, you should must use a language which fits best. This language is, in most cases, HTML5 and it says you should definitely prefer the above mentioned tags.

Will it affect your SEO?
Yes.

Are you able to notice it?
I don't know.

There was a great article about 4 years ago with interesting points in the comments.

Answer 2

The differences are their semantic functions, and I recommend referring to the W3 HTML specification for details rather than 3rd parties.

I suggest looking at the definitions in that specification for <em>, <i>, <b> and <strong> and using the one that conveys the correct meaning in each instance.

In terms of SEO impact, the benefit is that a search engine better understands the meaning of your text. That's essentially what HTML is for: it provides machine-readable semantic and structural information.

It's like the old adage about grammar being "the difference between knowing your shit and knowing you're shit". That apostrophe looks like a trivial detail, yet it's fundamental to understanding the meaning.

As search engines do more advanced language processing, voice search, understanding conversational patterns and so on, using HTML to correctly convey semantic and structural information could be critical to how your content performs.