A temporary, state-granted monopoly over an invention, given in exchange for public disclosure of how it works — a deliberate bargain between the inventor's reward and the public's freedom to use knowledge, and one of the most contested instruments of innovation policy.
In the 1790s, James Watt's patent on the steam engine was still in force. Other engineers had figured out how to make it far more efficient, but Watt's monopoly blocked them. When the patent finally expired, steam engine development accelerated. The story is contested — historians disagree about how much Watt actually slowed progress — but it points at the central paradox of the patent. The same legal tool that rewards an inventor for sharing an idea can also lock that idea away from everyone else for a generation.