> I was in a patent law class that spent the whole first day stressing, "you can't patent an idea; you can only patent an invention." And the words ring in my ears, "An invention is a an idea reduced to practice."
The problem with this reasoning is that the patent doesn't cover a _specific_ device or instance of a process, it covers all devices or all processes which happen to implement the ideas described in the patent. The monopoly isn't granted over a concrete good or service, or even exact copies, but over the _idea_ which encompasses all similar goods and services.
It would be true enough to say that the patent is _infringed_ by reducing the patented idea to practice, without a license. An abstract concept cannot infringe; for that you must build a device, or implement a process, based on the same idea. However, it is the idea which the patent monopolizes.
Or I suppose you could say that a patent grants you a monopoly over _other_ people's inventions, superseding (and infringing on) their own property rights, if those inventions happen to include a reduction to practice of the idea described in the patent. However, that puts patents in such an obviously bad light that their proponents would probably rather just say that patents cover ideas in the first place.