6. The aim of the Atomic philosophers was to explain the greatest number of phenomena by means of the fewest possible principles. This striving after unity or simplicity is indeed the great aim or characteristic of all philosophy. It is what we have frequently described as the pursuit of the universal in all things; and in joining in this pursuit the Atomists made but common cause, and had the same object in view, with the rest of their brethren. What we have to consider more particularly in regard to them is, first, the effect which their principles had in simplifying the theory of the universe; and, secondly, the effect which their principles had in simplifying the theory of human perceptions and sensations. These are the two points in which, I think, the interest of the Atomic philosophy centres: first, the tendency of their doctrine to afford a simpler explanation of the phenomena of the universe; and, secondly, a simpler explanation of man's perceptions than any hitherto propounded. I do not say that their explanation is true or successful, but it has, at any rate, the merit of simplicity. Let us consider separately each of the two points adverted to.
7. First, Before the time of the Atomic philosophers things were supposed to have qualitative as well as quantitative differences. That things differed from each in quantity, in size, in shape, and weight, for example, was sufficiently obvious; and it was thought to be no less obvious that they differed
