: a doctrine that the universe is composed of simple indivisible minute particles
: a psychological doctrine that perceptions, thoughts, and all mental processes are built up by the combination of simple elements
Philosophical doctrine that material objects are aggregates of simpler parts known as atoms. Atomism in the strict sense is characterized by three points: the atoms are absolutely indivisible, qualitatively identical apart from shape, size, and motion, and combinable with each other only by juxtaposition. Atomism is usually associated with realism and mechanism; it is mechanistic because it maintains that all observable changes can be reduced to changes in the configuration of the atoms that constitute matter. It is opposed to holism because it holds that the properties of any whole can be explained in terms of those of its parts.