In my last post, I undercut the idea the mere skepticism could ever cause reasonable doubt against self evident truths. But we can take this argument much further. It is simply not possible for any kind of skepticism against self-evident truths to be reasonable. Any such criticism would beg the question against self-evident truths, be self-refuting in practice and ultimately be undeniable.
The first general argument against doubting self-evident truths is that any doubt would beg the question against the truth that is to be doubted. An argument begs the question when the premises are less certain than the conclusion. So trying to convince an atheist that God exists by quoting the Bible is a prime example of question begging. Question begging is always irrational and unreasonable. Any argument against a self-evident truth will begin with premises that are less certain than the self-evident truth that they are questioning. Therefore, no argument against a self-evident truth is ever reasonable.
The second general argument against doubting self-evident truths is that any attempt to disprove a self-evident truth suffers from practical contradiction. Just as some truths are practically self-evident, their contradictories are practical contradictions. Stating “I am not talking” is a practical contradiction because anyone who says this says something false. In a similar way, any argument attempting to diminish trust in self-evident truths will depend on logical reasoning. But logical reasoning is a form of self-evident truth. Each step in the argument is logically self-evident given the prior steps (excluding the premises). So any attempt to undercut or rebut self-evident truths will require the use of those truths to do so. Therefore, any such argument is practically contradictory.
The third argument against doubting self-evident truths is that any attempt to doubt such truths will require using such truths as premises. We doubt our senses because we know of some instances when we have been deceived by illusions. But our deception is sensory and our recognition of that deception is also sensory. What is self-evident is that one of our senses must have been deceptive or our memory is deceptive. But this self-evident truth forms the basis of our doubt. Without such a self-evident basis, our doubt would not even seem plausible. Skeptical reasoning based on this doubt is flawed (see the first argument). But the self-evident truth is necessary to simply believe our doubts at all.
These arguments are sufficient to remove any remaining doubt regarding the usefulness and certainty of self-evident truths. The remaining questions involve recognizing which truths are self-evident and resolving arguments over that.