"necessary and proper" clause

Article I, section 8, clause 18. delegates legislative powers to Congress and authorizes all laws "necessary and proper" to carry out the enumerated powers (see federalism button). Clause is also sometimes called the "elastic" clause. While congressional authority is limited to its delegated powers, this clause allows Congress to choose the means by which it will execute its authority. The broad construction of this phrase has enabled the national government to adapt its powers to the needs of the times and has thus given the Constitution "elasticity" and thus reduced the need for frequent constitutional amendments.

Paraphrase from: The American Political Dictionary