distinction between two possible paths of inquiry: either “is, and must be” or “isn’t, and can’t be” (§291). The second path is rejected, because it involves trying to think about what is not: non-being is not something we can think or speak about meaningfully. There is actually a third path, mentioned a little later on, which is even worse: according to this path, we say both “is” and “is not.” This has the same problem that we would need to grasp non-being, but in addition leads to a contradiction: both is and is not.
