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,...
A sentence is an inverted sentence when the verb comes before the subject. An example would be : In the barn live the four horses. The verb is live. The subject is horses. The verb comes before the...