had not these principles to guide us in the arrangement and classification of our knowledge, it is manifest that our cognitions would have no unity, order, or coherence; our mental state would be no better than a chaotic dream. So essential are ideas to the existence of knowledge, so impotent are sensations, without ideas, to instruct us even in the most elementary truths.
27. This may further serve to illustrate a subject on which Plato has bestowed a good deal of elaborate treatment, the conversion, namely, of the human soul from ignorance to true knowledge. The ignorant and unconverted soul supposes that its knowledge of sensible objects is due to the impressions which it receives; the converted soul is aware that this knowledge is due, not to these impressions, but to the ideas of resemblance and difference (and some other ideas) by which these impressions are accompanied, but with which they are not by any means identical; in fact, that our whole knowledge of outward things is based entirely upon ideas, and is effected solely by their mediation.
28. From what has been already said in regard to the distinction and opposition between the particularity of sensation, and the universality of intellect, it is obvious that ideas cannot be the products of our sensible experience. Hence they must be referred to some other origin; they must be pronounced
