I've noticed that many sites and user interfaces tend to capitalize certain words or sentences like so:
Choose File Select a File to Upload Account Settings How to Format
but in some other cases, they don't:
Please select a file to upload to our system Browse the complete list of questions, or popular tags. Help us answer unanswered questions.
And sometimes, particularly in list items, all in lowercase. Are these good practices? What's a reasonable rule to decide when to capitalize or not, or even when to write all in lowercase?
I'm not sure that using title case (capitalizing the first letter in each word) can be described as correct or incorrect. FWIW, I have personally moved away from using title case in, say, checkboxes, radios, and list items. I now limit their use to one sentence, e.g. dialog title and button labels, e.g "Save File".
If it is a full sentence it looks wrong with all capitals.
On the other hand I sometimes capitalize short error messages ("Please Enter A Valid Email") even though it looks a bit weird for emphasis, but it is not something I would do all the time.
And I agree with @Hisham regarding simple menu options and labels
for example in a form I would write Full Name, Credit Card Number, etc..
but on top of the form if I wanted to put some instructions it would say something like "Please fill out the form below." just like any other normal sentence.
I tend to follow these guidelines:
When the sentence is in a contracted imperative form as:
Select File to Upload
-> the words are capitalized.
When the sentence is in full form as:
Please select a file to upload
Browse the complete list of files -> the words aren't capitalized
Mostly though, I think the choice is a design one. All lower case letter menus have a certain look and convey a different image than either all uppercase or proper case menus.
In English, both in computers and under the blue ceiling, title-style capitalization (capitalizing first letters of nearly all words) is for titles, and sentence-style capitalization (capitalize only the first letter for the first word) is for sentences. Titles generally include headers for your documents, pages, and sections therein and labels for controls. They are often sentence fragments lacking either the subject or predicate. Sentences are “regular” content, each generally including a subject and predicate, although sentences in the command sense often have “you” as the implied subject.
There are some gray zones. Style guides provide specific guidelines on when to use each. For example Apple recommends title-style for menu names, menu items, buttons, and any label that isn’t a full sentence. Apple recommends sentence-style for messages, check boxes, and radio buttons, even if they aren’t sentences.
However, style guides don't all agree with each other and sometimes they change. For example, the Windows UX Guidelines used to recommend title-style capitalization for buttons and menu items, but now recommends sentence-style capitalization. Title-style capitalization is only recommended for tabs, window titles, pages, programs, folders, and other “major components.”
In these gray areas, capitalization style is mostly a matter, of, uh, style. Sentence-style capitalization gives your app a more conversational tone, as if the user is interacting with an agent rather than a tool, which may or may not be a good idea in your case. I suspect title-style capitalization can make it easier to scan for key words in labels, but that’s just a hunch.
Capitalise or don't capitalise? The answer is simple: follow your company's style guide.
But I always tell my students: "Don't write your own company style guide, just use a published one from elsewhere."
Here is an existing style guide for text (including capitalisation) by Microsoft.
Here's why I advise my students to use an existing style guide:
I realise the above sounds cynical. There is a way to get an internal style guide written that has buy-in from those involved: a barn-raising. This involves your team sitting together, away from their usual desks, but with their laptops. Try once a week in a meeting room. Let people choose a topic to write from a list that the team has prioritised into high, medium, and low. Set a timer as you write. Writing time is quiet time. Each person writes a different topic, then the group reviews the topics together. After the timer goes off, review a topic if its writer feels it's ready for review. After the timer goes off, it's OK for one person to consult or poll others about their topic and then take it for another iteration before they ask the team to review it. Start the timer with 10 minutes; you can increase the writing time, as needed. Find a way to quickly share the topic that's being reviewed: via email, your LAN, a projector, etc.
English is full of examples of writers who think they should capitalize Every Word that they think is Special. It's an archaic style and it looks officious and a bit silly. Most modern style guides generally reserve capitalization for proper nouns, formal titles that are in apposition to people's names and the titles of cultural works or statutes. Sometimes a metanym gets a capital letter, for instance the Hill (Parliament Hill) or the City (London's financial district). A user interface shouldn't use title case as Choose A File isn't a title, it's an imperative sentence.