Overall, conjunctions serve to connect parts of a sentence. And, but, or, and yet are among the more common ones in English. Conjunctions can be classified by two things: their form, and their syntactic function. In regards to their form, conjunctions can either be simple or compound. This is determined simply by the amount of words they contain. Simple conjunctions are only one word, while compound conjunctions are either two words or a blend of more than one word.