Also called reductivism.
The reducing of certain kinds of entities, or of theories, or even of whole sciences, to other, more basic, ones; entities that are reduced may be replaced (‘Father Christmas is really Daddy’) or simply explained (‘Water is really H2O’).
Phenomenalism, for instance, reduces material objects, or sentences about them, to experiences, or sets of sentences about these. Similarly, one version of physicalism claims to reduce the other sciences to physics by showing that all their concepts and theorems can be expressed in terms of physics without loss of information.
Contrasting approaches include holism and emergence theories, though intermediate positions can be held.
Reductionism in general appeals to empiricists, nominalists, and others who use Ockham’s razor to achieve a sparse ontology (or list of what there is).
E Agazzi, ed., The Problem of Reductionism in Science (1991)