Does it matter if I use \textit or \it, \bfseries or \bf, etc

I typically use

\textit{Some italicized text}


while some of my colleagues use

{\it Some other text}


Should I bother changing one or the other, or does it matter?

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From l2tabu:

Why not use obsolete commands? Obsolete commands do not support LaTeX2e's new font selection scheme, or NFSS. {\bf foo}, for example, resets all font attributes which had been set earlier before it prints foo in bold face. This is why you cannot simply define a bold-italics style by {\it \bf Test} only. (This definition will produce: Test.) On the other hand, the new commands \textbf{\textit{Test}} will behave as expected producing: Test.

Apart from that, with the former commands there is no ‘italic correction’, cf. for instance halfhearted ({\it half}hearted) to halfhearted (\textit{half}hearted).

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To be fair, it's not really that hard to write {\it half\/}hearted. This is how it would be done in TeX, after all. –  TH. Aug 29 '10 at 2:27
It should be noted that when the blockquote talks about “obsolete”, it means obsolete in >= LaTeX2e. Those commands are not obsolete in Plain-tex or ConTeXt. –  morbusg Jul 29 '11 at 4:28

The \it syntax is inherited form LaTeX 2.09, and is regarded as supported 'for historical reasons only' in LaTeX2e. For bold, you should go for \textbf rather than \bf. For italic, you'd usually use \emph rather than \textit as it's semantic mark up and as it handles the italic correction automatically.

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I beg to differ. If you want to set italic text, \textit is the way to go. But if you want to emphasize some text, then you should use \emph{}. –  qbi Jul 28 '10 at 20:12
It's very rare that you want inline italic that isn't in some way semantic. For longer blocks, \itshape is the way to do things, of course. –  Joseph Wright Jul 28 '10 at 20:24
Of course, semantic markup should always be preferred over syntactic one, but the question was specific about the difference between \textit and \it –  Juan A. Navarro Jul 28 '10 at 20:45
Or, if you want a command that is used in the same way as \it, use \itshape. –  Sharpie Jul 28 '10 at 21:53
\emph is semantic: it says 'make things emphasised'. On the other hand, \textit means make this italic. By convention, \emph makes things italic, but you can redefine it to do something else (for example, the beamer class makes text red). On the other hand, \textit is always italic. So it is usually advised to use \emph in a document, using \textit only when you need definitely italic text. This might make a good question, as I'd then have more space to give detail! –  Joseph Wright Aug 18 '10 at 18:25

Hmm, I just posted this as an answer to another question, but just as I was posting, that question was closed—with a referral here. So I'll throw in my 2¢ here...

The reason I don't like \it and \bf is that they do not play well together. That is, they do not nest as one would intuitively expect:

Whereas \textit and \textbf do play well together:

This is nice. However, you may notice that it still fails to handle nested style adjustments to small caps, since the Computer Modern fonts do not contain slanted or bold small caps:

If this is a problem for you, then what I recommend—and I just happened to learn about this yesterday myself—is the wonderful slantsc package in combination with the lmodern package. slantsc provides, among other things, \rmfamily (roman), \ttfamily (typewriter/​teletype), \sffamily (sans-serif), \bfseries (boldface), \itshape (italics), \slshape (slant/​oblique), and \scshape (small caps). With these, small caps can obtained in slanted form:

As a bonus, slantsc fixes \textsl to behave properly with \textsc, so you can continue using those if you like.

Alas, I haven't yet found a package which fixes the behavior of nested instances of \textit. In typesetting, when you nest italics, you're supposed to come back out of italics to roman. For example, the word "Titanic" below is in nested italics:

Tanaka, Shelly. On Board the Titanic: What It Was Like When the Great Liner Sank. New York, NY: Hyperion/​Madison Press, 1998.

As a workaround, you can usually write \textrm to temporarily return to non-italics in those cases, but of course this is only valid if you know the exact number of nested italic levels, which may not always be the case, especially inside a macro.

Update:

As others have pointed out, \textit and \textsl do automatic italic correction, whereas \it, \itshape, \sl, and \slshape do not. Thus, you can write \textit{stuff}, but you must write {\it stuff\/} or {\itshape stuff\/} to get the same effect.

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I would not expect \textit (or any other command intended to do italics) to generate non-italic text. On the other hand I'd expect \emph (which is used to emphasize) to switch to italics if not already in italic mode while to switch off italics when in italic mode (because emphasizing is usually done this way). And guess what, that's exactly what \emph does. The correct way to type the title above therefore is: On Board the \emph{Titanic:} What It Was Like When the Great Liner Sank. Note that Titanic is emphasized, not italicised. –  celtschk Jan 20 '12 at 19:42
@celtschk: Cool, I did not know that! (Or I think I did once long ago and forgot!) Thanks so much for pointing this out. –  Todd Lehman Jan 23 '12 at 17:03
Note that cfr-lm will give you access to the same features but uses slightly different commands. cfr-lm relies on virtual fonts but also makes other features of the LM family available (e.g. different styles of figures, different weights etc.). Disclaimer: I wrote cfr-lm. –  cfr Dec 17 '13 at 23:46
@celtschk, ‘Titanic’ is not set in italics because it’s emphasized, but because its a custom of English typography to italicize names of vessels, like (family) names are set in small caps elsewhere. Therefore using \emph would be inappropriate. –  Crissov Jan 29 at 10:30