The elderly man didn't participate in the marathon because he knew it would enervate him. I will enervate and destroy my opponent. Shouted abuse from the fans could easily enervate a professional...
When it has a subject, verb, punctuation, capitalization, a predicate, and a complete thought. A sentence is a sentence when it is handed down by a judge (or a magistrate).
A sentence is a complete clause with a subject and a finite verb. A sentence fragment is not a complete clause, but is part of a clause (often lacking the verb to make a full sentence). For instance,...