The square, the most solid and material of geometric shapes, was used by Socrates to demonstrate the most highly ineffable of his philosophical doctrines, the immortality of the soul. We have, he observed, certain innate forms of knowledge which can be drawn out (educated) into our conscious minds. Knowledge, said Socrates, is recollection. The truths of number and geometry, for example, are within us, and we can either discover them for ourselves or, once they have been pointed out to us, we recognize them as old friends. If we have not been instructed in these things in this life, we must have learnt them in some other existence. In that case there is an immortal element in our beings—the soul.