Question – Just curious, which is the non-eligible subject matter?
Before the patent office even considers whether claimed subject matter can be awarded a patent, the office must consider whether that claimed subject matter is the type of thing that is patentable. For example, perpetual motion machines are not patentable because they don’t exist, and are therefore not “useful”. Similarly, claims to laws of nature (e.g., gravity) and mathematical algorithms are not patentable. At least since the Alice v. CLS Bank case in June 2014, when the Supreme Court addressed this issue head on, it has become quite difficult to patents software and business methods. The courts are still trying to figure out what to do, but among other things claims need to recite something that is happening in the real world. You can learn more about the current state of affairs on the web, and the patent office has provided quite useful guidelines here and here.