While it is generally accepted that intellectual property rights provide a method for increasing the rate of return for inventors, some economists believe there are a number of reasons to doubt whether patents provide:

a. sufficient incentives for innovation, as well as completely appropriate incentives for innovation

Explanation:

Some economists do not believe that providing intellectual property rights are enough to inspire or compensate for innovation and believe that even more rights should be given to inventors.

They also do not believe that patents are completely appropriate because they tend to expire eventually.