What May Have Been the Form of Matter
5 So that when herein thought seeks what the sense may arrive at, and says to itself, It is no intelligible form, such as life or justice, because it is the matter of bodies; nor perceptible by the senses, because in the invisible and formless there is nothing which can be seen and felt—while human thought says these things to itself, it may endeavour either to know it by being ignorant, or by knowing it to be ignorant.
Source: Confessions (New Advent)