Declare illegal is a phrase used to describe a legal action that prohibits a particular activity or behavior. The antonyms for declare illegal are legal, permitted, authorized, sanctioned, accepted, valid, and lawful. When a behavior is declared to be illegal, it stands to reason that the antonym of illegal would be legal. Similarly, if something is forbidden, its antonym would be permissive or authorized, indicating that something is allowed or accepted. The antonyms of the phrase declare illegal are essential in creating a balance in every legal system, where certain actions or behaviors can be recognized as lawful, and others may not.