Understanding is, or you could say, has evolved to be, ancillary to will and thus is limited in scope by the saliencies of the practical. On the other hand, the underlying categorial structures of any recognisable understanding are limited in number and are in this sense like those of computability. There may seem to be, or possibly be, or merely required to be, higher forms of understanding incomprehensible to us - as some might say would be needed for understanding our own minds, or brains - but all such qualitative distinctions resolve, as with computability, into differences of speed and memory, that is, differences in degree. So there are no in principle incomprehensible forms of understanding. Schopenhauer gets to the nub of this when he asserts that the end of all possible understanding is reached when it liberates itself from the will, that is from its own motives. What we see with the currently baroque explosion of critique is not a natural barrier to understanding but a refusal to admit that the nd has long been reached - the will's revenge on its prodigal child.