There are no rules.Would you please tell what kinds of structures or phrases can be used for titiles for essays or books? In my opinion, we may have a complete statement, a question,a V-ing form, a noun phrase and even a prepositional phrase perhaps as titles for essays or books. How about an imperative? And how about an incomplete statement like "Say yes to a class lesson presented in an entertaining and enjoyable way"? I find this incomplete sentence being used as a titile a little bit strange, but I'm not sure of my judgement. It was used by some of my students in their final test of English writing.
Thanks in advance.