The legality of a law concerning legality of possession of an object, committing an act, holding a belief is contingent upon the basis of law in a governed body. Speaking specifically of the US, the Constitution dictates what laws may be made on a matter, who may make them, the manner by which they are to be ratified, and in what manner they may be enforced. Determine what law or laws you are potentially breaking or about to break and then whether it/they was/were ratified Constitutionally.