magnitudes; yet they do it not for fear of missing of the equality, but to avoid inconvenience or trouble. But you (you, I say), that have no definition of equals, neither received from others, nor framed by yourselves, out of your shallow meditation and deep conceit of your own wits, contend against the common light of nature. So much is unheedy learning a hinderance to the knowledge of the truth, and changeth into elves those that were beginning to be men. Again, when men inquire the equality of two bodies in length, they measure them by a common measure; in which measure they consider neither breadth nor thickness, but how the length of it agreeth, first with the length of one of the bodies, then with the length of the other. And both the bodies whose lengths are measured, are successively in the same place under their common measure. _Place_ therefore in lines also, is the proper index and discoverer of equality and inequality. And as in length, so it is in breadth and thickness, which are but lengths otherwise taken in the same solid body. But now when we come from this equality and inequality of lengths known by measure, to determine the proportions of superficies and of solids, by ratiocination, then it is that we enter into geometry; for the making of definitions, in whatsoever science they are to be used, is that which we call _philosophia prima_. It is not the work of a geometrician, as a geometrician, to define what is equality, or proportion, or any other word he useth, though it be the work of the same man, as a man. His geometrical part is, to draw from them as many true and useful theorems as he can. You object secondly, that a pyramis may be equal to a cube whilst it is a pyramis. True. And so also whilst it is a pyramis it hath a possibility by flexion and transposition of parts to become a cube, and to be put into the place where another cube equal to it was before. This is to argue like a child that hath not yet the perfect understanding of any language. In the third and fourth objection, you teach me to define equal bodies (if I will needs define them by place) by the _equality of place_, and to say, _that bodies are equal that have equal places_. Teach others, if you can, to measure their grain, not by the same, but equal bushels.