Capitalization seems to be a weak point for many in software. Perhaps because code (and odd company names) teach us that words can have a capital letter in the middle, capitalization of UI text is often more creative than is strictly necessary.
Capital letters aren’t important only because some of your users are grammar geeks; they’re important because they’re nice visual clues. They show clearly where a sentence starts, the difference between title and sentence, what’s a name and what’s a verb. But most importantly there are some – perhaps your potential funders – who will assume, if you avoid capital letters, that you simply didn’t learn how to use them.
Now, the truth is that capitalization is a delicate business. If you want to really get into it, which I encourage, find your style guide and get going. I assume, however, that you’re not that interested. This will do for most UI decisions.
Title Case or Sentence Case?
Capitalization changes between style guides, and you’ll find that different software companies have different habits. This primarily reflects the tone they’re trying to convey: the fewer capital letters, the less formal they appear. The choice that most affects your tone is between title case and sentence case (discarding, as I already have, the choice of not capitalizing anything at all).
Title case is the form of capitalization where any word that can be capitalized – is (I’ll explain later which words do this). The title of this article, and all its sections, are in title case. Title case seems more formal, so some people dispense with it altogether and use only sentence case. It’s your choice – just be consistent.
In sentence case, only the first letter of the sentence is capitalized, except for words that are always capitalized (I’ll explain that later, too). This is the main advantage of sentence case over title case: it’s very simple to learn.
The most common places to use title case
1. Window and pop-up titles.
2. Titles of sections of the window (like a field group).
3. Buttons with more than one word.
4. Navigation menu options.
5. Field names.
In the end, it’s all about consistency: use or don’t use title case to your liking, but uniformly across the entire UI.
Places that should never use title case
1. Listed options (including drop-down lists, radio buttons, check boxes etc). This is especially true if the list is numbered.
2. Tool-tips and information bubbles.
Word by Word
Words That Are Always Capitalized
Some words are capitalized in sentence case, even when they’re not the first word of the sentence. For the purposes of UI, you mostly need to know the following:
1. Proper names: people, countries.
2. Titles like Dr and Mr.
3. Organization and company names: follow their official capitalization (check their website if you’re not sure). Software companies are especially likely to have non-standard capitalization (and oddly placed hyphens).
I follow the official spelling of names even if the name is the first word of a sentence. For example, a sentence beginning with “iPhone” will begin with a lower-case I. If you don’t like the way that looks, the easiest solution is to rework the sentence so that it’s no longer the first word.
Words That Are (Almost) Never Capitalized
Some words are not capitalized even in title case, unless they’re the first word of the sentence. The most common are: a, an, and, at, by, for, from (some style guides dispute this; pick whatever you like, just be consistent), in, of, off, on, or, so, the, to, too, up, yet. There is one exception here: if the word is part of a hyphenated compound, it is capitalized along with the other words in that compound.
As I said earlier, there’s actually more to it than this – but you probably don’t want to know.
Now, something you might have expected to find on this list is the various forms of the verb “to be”. Many people don’t capitalize words like “is” and “was” in title case; I often don’t, because it’s so jarring to see them with capital letters that I simply forget. But they are verbs, and should therefore be capitalized.
1. When referring to a keyboard key, capitalize the first letter of every word in the name. Tab, Enter, Page Up, Num Lock.
2. There is a difference between initials and acronyms (initials read as a word): with initials, use all-caps: ID, PTZ, VMD. With acronyms, initialize only the first letter: Nasa, Nato. As I said earlier, neither of these rules applies if the name is copyrighted (or is in official use) in some other manner; always follow the official form.
Note that there are exceptions, such as CD-ROM, where ROM is pronounced as a word but is in all-caps.
3. Geographical areas that are widely known under a collective name can be capitalized. So if you’re breaking something down to regions, it’s Middle East, North Atlantic, East Asia etc.
4. I think there’s something very old-school about Internet and Web. Too old school; lower-case those words to internet and web. Also dotcom, online and all words beginning with cyber.
5. It’s lower-case e in e-mail and e-commerce (and many people, and style guides, have dispensed with the hyphen).
Capitalizing After Punctuation Marks
The simple ones
1. After a full stop: yes.
2. After a comma: no.
3. After an exclamation mark: yes, but don’t use them in your UI.
4. After a semi-colon: no. And I question the wisdom of a sentence in any UI that requires a semi-colon.
5. After a question mark: yes.
The complicated ones
Text after colons and dashes, and text within brackets, is only capitalized in some cases. If you’re interested in the details, read your style guide. If you’re not, then for consistency’s sake I suggest you never capitalize after these.