Yet the enterprise called science is predicated on the audacious belief that, in spite of appearances, nature is both ordered and intelligible to us. Scientists assume that hidden beneath the surface complexity of the world lies a harmonious law-like simplicity. It is the job of science to uncover this hidden order, and thereby reveal the rules that govern the operation of the cosmos. This ambitious project has been greatly facilitated by the philosophy of reductionism. In its commonly discussed form, reductionism is the hypothesis that complicated wholes are composed of simple parts, and that an understanding of the whole may be attained by knowledge of the individual component parts.
Reductionism is an ancient concept, dating from the Greek school of atomism.
Democritus and Leucippus taught that the universe consists of nothing more than atoms moving in a void. The atoms were supposed to be truly primitive and indestructible entities, without internal parts. The immense richness and variety of material objects were accounted for by the different types of atoms they contain, and everything that happens in the universe is attributed simply to the rearrangement of atoms. The objects that scientists today call atoms are not the basic level of matter that the Greeks had in mind. They are composite bodies with smaller pieces within them.