Can man, who is stuck in the middle knowing neither the end or the beginning, “validate knowledge” as you would say? I take a more humble position and say I don’t think we can “validate knowledge.” I do not think we can “establish truth.” That’s just not an ability that we have. I understand that you see faith as being aligned with imagination, hope, whim, and such. And, you say that reason alone is how we acquire and validate knowledge. And, I understand your hierarchy of perceptions to concepts to propositions to certain knowledge. But, is what we perceive to be the case actually the case? It’s not entirely self evident. And If we believe to be real what our five senses report to be the case, we still must believe that our cognitive faculties can form correct and accurate concepts from the input of our senses. In other words, we believe that the whirring and buzzing that is going on in our heads has a one to one ratio with the universe and corresponds with what is actually the case. And, where there is belief, there is faith. So, even at the most fundamental level, where you talk of perception, believing a perception is accurate is still necessary since humanity has not been able to prove its accuracy or validity. We can operate with what we’ve been given, but we have not been able to establish truth. In fact, inasmuch as humanity says that it can validate knowledge or establish truth they are doing so by whim and fancy. I say, we must believe by faith that things are true and that our knowledge is correct. Those who have faith have recognized our limitations. Faith is sane because it floats easily in an infinite sea. Those who only have reason seek to cross the infinite sea, and so make it finite. The result is mental exhaustion. To accept everything is an exercise, to understand everything a strain. The man of faith only asks to get his head into the heavens. It is the logician who seeks to get the heavens into his head. And it is his head that splits.
You say, “Any “error” or “uncertainty” at the perceptual stage would be an impossibility — and as absurd to speak of as it would be to speak of “error” or “uncertainty” with regard to automatic functions, like breathing, digestion, etc.” But, automatic functions do have error and uncertainty. I am a living testimony to it. My digestive system does not work properly. It is in error, and the outcome of whether or not I will have a proper bowel movement is uncertain. The senses can go terribly wrong too. The eyes grow dim over time so that they don’t function properly. A friend of mine has her taste buds all screwed up so that the things she once thought sweet have a metallic taste to them. Her sense of smell is off as well. Error at the perceptual stage is a possibility, therefore your statement is overbold. You might say that, if the senses are working properly, then perceptual error is an impossibility, but that too has problems. How do you define normal sense perception? Where is your measuring stick? Cannot all of humanity be inflicted with the same deformed eyesight and not know it? Because we all, whose senses work, might feel a rock to be hard, says nothing about what might actually be the case. The problem for humanity remains, “Is what I percieve to be the case, actually the case?” And you have done nothing to show that the two match each other except to say dogmatically that it is impossible that they don’t match. Like I said, It’s a very bold statement, and one, I think, that cannot be proven.