Final answer:
State constitutions have the function of establishing civil liberties and forbidding certain government actions.
Step-by-step explanation:
A function of a state constitution is to forbid certain government actions by establishing civil liberties. State constitutions provide a set of rights and protections for individuals, limiting the power of the government. For example, the Bill of Rights in state constitutions protects freedoms such as freedom of speech, press, and assembly. These constitutional provisions ensure that citizens' rights are preserved.