And, but, and or often appear without a comma when the clauses they join are short. Adverbial connectives are words like therefore, however, nevertheless, consequently, hence, accordingly, moreover, furthermore, besides, indeed, and in fact . Perhaps he will call again. Often a modifier merely gives further information about something already identified. It is nonrestrictive.
Nonrestrictive material is set off from the rest of the sentence by a comma.
Use a comma both before and after if the nonrestrictive material occurs in the middle of the sentence. Her aunt, the lawyer, lived in Boston. We visited the place, a vegetarian restaurant. We saw the bride, dressed in white. She talked to her lawyer, a well-known attorney.