Note 58 — LOGIC

An identical proposition is not an inference; but all reasoning consists in inference, or in finding out one thing as implied in another. In comparing any two objects, I have nothing previously given and cannot predict the result; but having made the comparison, I have then something determined and fixed to go by; and what else I discover or imagine must be in conformity with this first knowledge. This coherence in propositions, or in the mind, is the force of reason, whereby one idea acts as the ground-work or cause of another. If I apply B as a common measure to A and C, and find it the same with both, it follows that they are equal to one another; since otherwise I must suppose the same thing (B) to be equal to unequal things, which is impossible as long as I retain my senses, or more properly, my recollection. I have ascertained two lines to be of the length of a third; that length cannot differ from itself; and therefore having settled what the two lines are with respect to the third, I cannot conceive them to be different with respect to one another, without forgetting myself, or what I know of them. If I had no power of contemplating different propositions together, I could draw no such conclusion; the conclusion therefore results from this comprehensive power of the mind; and reason is the end or band that ties the bundle of our separate ideas, or the logical fasciculus together.