English grammar doesn't prohibit ending a sentence with a preposition, but unless the sentence is very short, the practice is usually poor style. The guideline follows as corollary to an overarching principle of English style: the sentence's end position should be exploited to convey new information, a function it performs with unique effectiveness. According to some critics, manipulating word order is the skill today's writing instruction for professionals most neglects; debunking the myth that the hanging preposition is ungrammatical endears these constructions to writers unmindful of word order.
Wayne Schiess (http://tinyurl.com/yab9ddj) gives an example of a sentence that should end in a preposition; compared to the stilted and verbose Sentence 1:
A lawyer attending one of my seminars offered a great suggestion of which I had never thought,
Sentence 2 is more natural and concise:
A lawyer attending one of my seminars offered a great suggestion that I had never thought of.
Has Wayne demonstrated that effective style permits commonly ending sentences with a preposition? No, the writer can avoid the hanging preposition's limpness, sound natural, and be more concise by thinking outside the verb, as in Sentence 3:
A lawyer attending one of my seminars offered a great suggestion I had never considered.