Comment by math

Most of the time, I don't think you do. I think innovation is still going to happen anyway. For example, I think companies would have still made mobile phones and furthermore I think they would be better without patents because one maker wouldn't be arbitrarily restricted from using some idea-that-was-going-to-happen-anyway-because-the-time-was-right because another patented it. What is lost in monopolies is more than made up for in reduced overhead and ability to move quicker and come up with superior solutions because you are allowed to build on more ideas than you otherwise would. In some instances perhaps patents do act to expedite innovation (instances where time/cost to market is very high), but I think these are in the minority and that there is probably a better legal / tax / grant / political solution to that than granting of monopolies on ideas.