That is all good and valid, and of course I don't believe in any results of deductions with errors in them just based on said deductions. But that has nothing to do with reality. Two pebbles plus two pebbles resulting in three pebbles is not what convinces me that SS0 + SS0 = SSS0; finding the error is, which is nothing that is perceived (i.e. it is purely abstract).

If we're defining "situation" in a way similar to how it's used in the top-level post (pebbles and stuff), then there simply can't exist a situation that could convince me that SS0 + SS0 = SSSS0 is wrong in peano arithmetic. It might convince me to check peano arithmetic, of course, but that's all.

I try to not argue about definition of words, but it just seems to me that as soon as you define words like "perception", "situation", "believe" etcetera in a way that would result in a situation capable of convincing me that SS0 + SS0 = SSS0 is true in peano arithmetic, we are not talking about reality anymore.