Representatives introduce a bill while the House is in session by placing it in the "hopper" on the Clerk's desk. It is assigned a number and referred to a committee which studies each bill intensely at this stage. Drafting statutes requires "great skill, knowledge, and experience" and sometimes take a year or more. Sometimes lobbyists write legislation and submit it to a member for introduction. Joint resolutions are the normal way to propose a constitutional amendment or declare war. On the other hand, concurrent resolutions (passed by both houses) and simple resolutions (passed by only one house) do not have the force of law but express the opinion of Congress or regulate procedure. Bills may be introduced by any member of either house. However, the Constitution states, "All Bills for raising Revenue shall originate in the House of Representatives." While the Senate cannot originate revenue and appropriation bills, it has the power to amend or reject them. Congress has sought ways to establish appropriate spending levels.