Comment by shagie

Kind of, not really though. You can't patent the same thing again.

> 35 U.S.C. 101 has been interpreted as imposing four requirements: (i) only one patent may be obtained for an invention;

You need to improve upon it and have a new claim.

If I was to patent A and make it, and then patent B which improves upon A at some point in the future, when A's patent expires someone else can make A and if they show that they're making A and not B, there's nothing I can do about it.

The issue is that often B is better than A (why make a 223,898 light bulb when you can make a 425,761 light bulb?) so while you could make A, its not commercially viable to do so.

The thing is that I've got a research line looking at making improvements on B and patenting C later which is a further improvement on B. The investment of time, knowledge, and resources to be able to do refinements of A to make B, C, and later D - that's where it's hard to get into it.

Someone else could improve on A to make B' and if it was different than how I did B, they could patent that. Though in the real world, this often involves in hiring away people who are familiar with A and investing a lot of time / money into making a B' that might get interpreted by the courts as too similar to B.