148. For convenience in treatment, unlawful agreements may be classified, according to their matter or object, as

(a) Agreements in violation of positive law; and

(b) Agreements contrary to public policy.

The distinction here made between agreements in violation oi positive law and agreements contrary to public policy is in the reasons which determine the law to hold the agreement void, and not in the nature or operation of the law itself. The nullity of the agreement itself is in every case a matter of positive law;2 but in one class of cases the acts contemplated by the agreement are prohibited by the common law or by statute, while in the other the prohibition rests more particularly on public policy, or, as it is sometimes called, the "policy of the law." It is not always easy to distinguish between the two classes, for frequent decisions upon certain matters of public policy have established such definite rules regarding them that they are in effect rules of the common law. Too much importance, therefore, must not be attached to any classification of the subject.