St. Thomas Aquinas, in his Commentary on Boethius’ De Trinitate, insisted that although sensorial images (phantasms in the jargon of scholasticism, symbols in a more contemporary English usage) accompany every act of intellection, they operate in a peculiarly negative fashion in metaphysical discourse. 1 Metaphysical reasoning, even though it aims at concluding to truths about those principles that need not exist in matter and motion, nevertheless is human and hence follows the pattern proper to man’s entire cognitive life. The metaphysician, as do all men, uses phantasm symbols, but he must deny that that which he is talking about—namely, being—is or exists as it is presented to him in the image. 2 A negation of any positive representational function in the phantasm includes, of course, the conceptual content presented therein. A striking example of this teaching is found in St. Thomas’ doctrine on substance. Although first philosophy separates substance from any necessary link with matter and motion—substances can be in matter but do not have to be in matter—nonetheless, the only proper concept of substance available to an intellect whose act is proportioned to the scope of material things, is that of a material substance. 3 Our concepts are properly those of material essences. 4 Therefore, the metaphysician must drop the concept, not in the sense of suppressing it but of holding it before his mind and then negating it. Borrowing a trick from Heidegger, this can be visualized in the following way:

phantasm/concept; phantasm/concept.