we endeavour to express our understanding of Nature. We have to analyse and to abstract, and to understand the natural status of out abstractions. At first sight there are sharp-cut classes within which we can sort the various types of things and characters of things which we find in Nature. Every age manages to find modes of classification which seem fundamental starting points for the researches of the special sciences, Each succeeding age discovers that the primary classifications of its predecessors will not work. In this way a doubt is thrown upon all formulations of laws of Nature which assume these classifications as firm starting points. A problem arises. Philosophy is the search for its solution.
Fox example, we can conceive Nature as composed of permanent things — namely, bits of matter, moving about in space which otherwise is empty. This way of thinking about Nature has an obvious consonance
