I find this to be fascinating question. To answer most questions, we use our reasoning faculties to arrive upon an answer, yet, in this case, such a move is not necessarily allowed. To do so would be to descend into circular reasoning: you use rational thinking to decide whether or not rational thinking is a reliable way of knowing. To even think about this question, we automatically assume that rational faculties are reliable and offer a generally reliable way of making sense of reality. I do not know about anyone else, but I am hard pressed to even begin to imagine what an alternative would look like. If not rationality, how else are we to make sense of reality? How ironic that the very faculties we use to discern the validity and verity are themselves without means of verification. How do we really know that that by which we discern reliability from unreliability is itself reliable and an adequate tool for such tasks?
Assuming for the moment that we are evolutionary naturalists, how do we know that our reasoning capacities have evolved with reliability being favored? Reliability is not always necessary for survival. The antelope that runs at the rustling of the grass around the water hole will probably survive longer than the antelope that stays around to see if the grass moved because of the wind or because of a predator.
One of my pet peeves is when Christians forget that our sinful nature affects every part of our humanity, including our reasoning. The consequence of sin is that we no longer reason without error. Our thinking is faulty and broken, though not completely useless. By itself, it is not a solid basis for knowing. Only when human rationality can be tested against the revealed truth in the Scriptures can we know if our rationality is working correctly or not.