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Rh. We must endeavour to apply this rule to the present case.

18. In dealing with the philosophy of Socrates, I touched on several truths which carry us a considerable way, I think, towards a right understanding of the Platonic ideas; these were the universality of ideas as contrasted with the particularity of sensations, the activity and freedom of the mind, its emancipation from the bondage of sensation, evinced in its rising into the region of ideas even in its lowest and most ordinary cognitions. I am not sure that I have very much to add to the explanation of ideas there given, but I shall endeavour to present it in a somewhat new light, and under a somewhat different point of view.

19. Let me dwell, first of all, on the necessity of ideas, the necessary truth which is their main characteristic. You have all heard of necessary truth, and understand, I daresay, something of its nature. Necessary truth is truth which the mind cannot help acquiescing in; it is truth for all minds, and not truth merely for this or that particular kind or order of minds. Such truths are the axioms of geometry, and indeed all mathematical truth. Necessary truths are those of which the opposites are absurd, inconceivable, contradictory. In explaining, then, the necessity of ideas, what I wish to show you is, That ideas are essential, are absolutely indispensable to