I used this argument in a different forum and decided that it needs its own topic simply because it is so unusual and counter-intuitive.

There is no way to be certain that logic is valid. We can divide any possible argument into the two categories of logical and illogical. Since anything that is not logical is by definition illogical, and vice versa, these are the only two possible categories. My argument follows inevitably from these simple and indisputable premises.P1: Every argument is either logical or illogical.P2: Any attempt to use logic to prove that logic is valid is circular, because the use of logic presumes that logic is valid.C1: It is impossible to use logic to prove that logic is valid.P3: Any attempt to use illogic to prove that logic is valid is inherently contradictory.C2: It is impossible to use illogic to prove the validity of logic.C3: Because of P1, C1, and C2, there is no possible argument that can prove that logic is valid.As a result, no matter how self-evident logic seems or how well it is supported by the evidence, we cannot prove that logic is valid because such arguments are logical and therefore circular. Since it is impossible to be certain that logic is valid, and since all knowledge is dependent on the validity of logic, it is impossible to be absolutely certain that knowledge is true. Consequently, knowledge cannot exist, since any knowledge would be based on the uncertain assumption that logic is valid.

So what do you think? I'm guessing we all agree that logic is valid, but do you think it's possible to prove that logic is valid? Is my reasoning correct, or does it have a flaw(s)?

In other words, can we prove logic is valid, or do we just have to assume that it's valid out of necessity?