It is from this standpoint that Leibniz criticises what Locke says about the relation of sensations to the objects which produce them. Leibniz holds that all our sensations have a definite and natural connection with the qualities of objects,--the "secondary" as well as the "primary." They all represent certain properties of the object. Even the pain which the thrust of a needle gives us, while it does not resemble anything in the needle, does in some way represent or resemble motions going on in our body. This resemblance is not necessarily one of exact form, but just as the ellipse, hyperbola, and parabola are projections of the circle in the sense that there is a natural and fixed law of connection between them, so that every point of one corresponds by a certain relation with every point of the other, so the resemblance between the sensation and the quality of the object is always in the form of a fixed law of order, which, however unknown to us it may now be, is capable of being found out. If we are to make any distinction between "secondary" and "primary" sensations, it should be not that one presents qualities that are in the objects, and the other affections which exist only in us, but that the primary sensations (of number, form, size, etc.) represent the qualities in a distinct way, appealing to the rational activity of intelligence, while the secondary represent the qualities in a confused way, a way not going beyond the effect upon the mind into relations, that is, into distinct knowledge. This brings regularly before us the question of the relation of sensations to knowledge. We have seen enough already to know that Leibniz does not believe that knowledge begins with the simple (that is, unrelated), and then proceeds by a process of compounding. The sensation is not simple to Leibniz, but thoroughly complex, involving confusedly within itself all possible relations. As relations are brought forth into distinct light out of this confusion, knowledge ends rather than begins with the simple. And again it is evident that Leibniz cannot believe that knowledge begins and ends in experience, in the sense in which both himself and Locke use the word; namely, as meaning the combination and succession of impressions.