21 R. Tell me now what science contains the principles of definitions, divisions and partitions. A. It has been said above that these are contained in the rules of disputation. R. Grammar therefore, both as a science, and as a true science, has been created by the same art which has above been defended from the charge of falsity. Which conclusion I am not required to confine to Grammar alone, but am permitted to extend to all sciences whatever.
For you have said, and truly said, that no science occurs to you, in which the law of defining and distributing does not lie at the very foundation of its character as a science. But if they are true on that ground on which they are sciences, will any one deny that very thing to be truth through which all the sciences are true? A. Assuredly I find it hard to withhold assent: but this gives me pause, that we reckon among the sciences even that theory of disputation. Wherefore I judge that rather to be truth, whereby this theory itself is true. R. Your watchful accuracy is indeed most highly to be commended: but you do not deny, I suppose, that it is true on the same ground on which it is a theory and science. A. Nay, that is my very ground of perplexity.
For I have noted that it also is a science, and is on this account called true. R. What then? Do you think this could be a science on any other ground than that all things in it were defined and distributed? A. I have nothing else to say. R. But if this function appertains to it, it is in and of itself a true science. Why then should any one find it wonderful, if that truth whereby all things are true, should be through itself and in itself true? A. Nothing stands now in the way of my giving an unreserved assent to that opinion.
Source: Soliloquies (New Advent)