It explicitly requires that there must be time limits. That isn't required if all you want to do is reward innovation. The time limits are required because the ultimate purpose is to enrich everyone, which means that everyone gets access once the inventor has gotten a fair shake. For patents in particular, it is well-established in the law (though poorly followed in practice) that a patent ought to serve as a guide to replicating the invention, with the inventor being assured that no one can do so without his permission until the patent expired.
Unfortunately the time limits are useless if they are allowed to grow them indefinitely. In the US, the copyright length has extended from 14 years (with another renewal for 14 years) to life + 70 years. There's nothing fair in Life + 70 years.
On patents - they were meant to replace the need for trade secrets, unfortunately most patents that pass these days is for things that can be replicated without looking at the patent's application. And while I understand somewhat the need for patents in the health-care industry (only to a certain extent, since on the other hand access to quality health-care should be a basic right), the situation we are in is completely ridiculous.
In the end, the inventor already benefits by being first to market and a patent is only morally justified if the research costs were too big, allowing the inventor to recover those costs in the face of potential competition that may replicate the results and for which those costs weren't an issue. On the other hand, if patents would disappear tomorrow, I'm pretty sure that people would still go on, building and inventing things. So the benefit to society at large is questionable.
