No individual, other than a member, in good standing, of the bar of this commonwealth shall practice law, or, by word, sign, letter, advertisement or otherwise, hold himself out as authorized, entitled, competent, qualified or able to practice law; provided, that a member of the bar, in good standing, of any other state may appear, by permission of the court, as attorney or counselor, in any case pending therein, if such other state grants like privileges to members of the bar, in good standing, of this commonwealth.
Massachusetts Legal Code