Thus, at the lowest end of the scale, we have what we call inanimate matter, which Aristotle thinks of much as we do, namely, as something occupying space, the different parts of it being endowed with different powers of movement, and with different properties, such as warmth or coldness, wetness or dryness. A natural thing, he says, is a thing that has a principle of activity in itself, something that makes it act in a definite way, whenever it is not interfered with by anything else.[18] Aristotle speaks, for example, of fire having a natural tendency to mount up, much as we might speak of solids having a natural tendency to gravitate towards one another. Go back as far as we like, and, Aristotle thinks, we still find certain primitive differences which constitute what we call the primitive elements. This, I imagine, is much the point of view of modern science. And these primitive elements in Aristotle's view influence each other, unite with each other, or change into each other. As a rule, however, they exhibit no new powers. But given a happy concurrence of qualities, say a certain union of heat and cold, and a new power does become manifest: the power of life. Thus, in a sense, Aristotle does envisage the spontaneous generation of life; and he knows, roughly, what he means by life. The living thing can go through far more changes than the non-living, while yet remaining recognizably the same thing. For example, it shows in itself a greater advance to richness and also a decline, it uses other things to foster this advance, and it sends out fresh things, like itself, but independent of itself: in short, it grows, decays, feeds itself, and propagates its kind.[19]