>Sorry, you can't read a rule on this practice, Because It Is Entirely Arbitrary.
Don't say that.
Since most newspapers and magazines are struggling to survive, maybe they don't do it any more, but for decades they made all their publications conform to style guides which were often as lengthy as books. Other organizations and communities of writers also used style guides. Three famous style guides:
Also the New York Times maintained their own style guide, which I seem to recall was also sold to the general public. The whole point of these guides was to make written English more consistent.
As to the specific question of capitalization style, there is one very dominant style: namely, articles ("the", "a" and "an"), prepositions and conjunctions ("and", "or", "but" and maybe one more I cannot remember right now) are not capitalized, but everything else is.
> for decades they made all their publications conform to style guides ...
Of course I know that, in fact my AP Style Guide is within arm's reach, and I regularly use Strunk & White as a source for a particular style position, but (apart from "make every word count") these references don't apply to online text, the present topic. Online style isn't print style -- the former isn't formalized to the degree that print style is.
I will know when there's a formal online style, widely accepted, because the first principle will be "no more gray text on a gray background!" I won't hold my breath.
Don't say that.
Since most newspapers and magazines are struggling to survive, maybe they don't do it any more, but for decades they made all their publications conform to style guides which were often as lengthy as books. Other organizations and communities of writers also used style guides. Three famous style guides:
(1) http://en.wikipedia.org/wiki/A_Dictionary_of_Modern_English_... a.k.a. Fowler's; and
(2) A Chicago Manual of style (which might have been limited mainly to academic writing; do not remember); and
(3) http://en.wikipedia.org/wiki/The_Elements_of_Style a.k.a. Strunk and White.
Also the New York Times maintained their own style guide, which I seem to recall was also sold to the general public. The whole point of these guides was to make written English more consistent.
As to the specific question of capitalization style, there is one very dominant style: namely, articles ("the", "a" and "an"), prepositions and conjunctions ("and", "or", "but" and maybe one more I cannot remember right now) are not capitalized, but everything else is.