In general, when a piece of text, such as a title or a headline, contains initial caps, the following words should not be capitalized:

Nouns, pronouns, verbs, adjectives and adverbs are always capitalized, no matter how short. So are prepositions of four letters or more.
Of course, the first word in a title, headline or similar piece of text is always capitalized, no matter what part of speech it is, or its length.


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