In philosophy, intelligibility is what can be comprehended by the human mind in contrast to sense perception. The intelligible method is thought thinking itself, or the human mind reflecting on itself.  Plato referred to the intelligible realm of mathematics, forms, first principles, logical deduction, and the dialectical method. The intelligible realm of thought thinking about thought does not necessarily require any visual images, sensual impressions, and material causes for the contents of mind.  Descartes referred to this method of thought thinking about itself, without the possible illusions of the senses.  Kant made similar claims about a priori knowledge. A priori knowledge is claimed to be independent of the content of experience.