Can any part of speech be used to start a sentence as long as the sentence has a subject and predicate and is correctly structured.

The parts of the sentence are a set of terms for describing how people construct sentences from smaller pieces. There is not a direct correspondence between the parts of the sentence and the parts of speech - - the subject of a sentence, for example, could be a noun, a pronoun, or even an entire phrase or clause. Like the parts of speech, however, the parts of the sentence form part of the basic vocabulary of grammar, and it is important that you take some time to learn and understand them.