[Carol]

Art. 1, Sec. 8. "The Congress shall have power . . . To promote the progress of science and useful arts, by securing for limited times to authors and inventors the exclusive right to their respective writings and discoveries."

I don't work on copyrights, but I can explain the patent system. In order to prevent inventors from keeping their inventions as trade secrets, and to in order to share knowledge and allow others to build on that knowledge, an inventor is allowed exclusive right to sell and practice their invention for a limited time.** But, to get these rights, the inventor must teach others how to practice and make their invention. So it's a tradeoff. An inventor can reap the benefits (= make $) by keeping their work as secret, with the risk someone would discover it independently, or can tell everyone how to do it but get a guaranteed period of time where they are the only ones allowed to sell and practice the invention.

Of course some inventions can't be kept secret, such as a better mousetrap. So why would someone spent time and effort to develop a better mousetrap unless they know they can recoup their money by selling the mousetraps before competitors copy them and sell them as well? That is what the patent system is trying to encourage - to promote innovation by making it cost-effective to spend money on research and development.

**The life of a patent is 20 years from the filing date. It used to be 17 years from the issue date.