unity of science a situation in which all branches of empirical science form a coherent system called unified science. Unified science is sometimes extended to include formal sciences (e.g., branches of logic and mathematics). ‘Unity of science’ is also used to refer to a research program aimed at unified science. Interest in the unity of science has a long history with many roots, including ancient atomism and the work of the French Encyclopedists. In the twentieth century this interest was prominent in logical empiricism (see Otto Neurath et al., International Encyclopedia of Unified Science, vol. I, 1938). Logical empiricists originally conceived of unified science in terms of a unified language of science, in particular, a universal observation language. All laws and theoretical statements in any branch of science were to be translatable into such an observation language, or else be appropriately related to sentences of this language. In addition to encountering technical difficulties with the observational–theoretical distinction, this conception of unified science also leaves open the possibility that phenomena of one branch may require special concepts and hypotheses that are explanatorily independent of other branches.
Another concept of unity of science requires that all branches of science be combined by the intertheoretic reduction of the theories of all non-basic branches to one basic theory (usually assumed to be some future physics). These reductions may proceed stepwise; an oversimplified example would be reduction of psychology to biology, together with reductions of biology to chemistry and chemistry to physics. The conditions for reducing theory T2 to theory T1 are complex, but include identification of the ontology of T2 with that of T1, along with explanation of the laws of T2 by laws of T1 together with appropriate connecting sentences. These conditions for reduction can be supplemented with conditions for the unity of the basic theory, to produce a general research program for the unification of science (see Robert L. Causey, Unity of Science, 1977).
Adopting this research program does not commit one to the proposition that complete unification will ever be achieved; the latter is primarily an empirical proposition. This program has been criticized, and some have argued that reductions are impossible for particular pairs of theories, or that some branches of science are autonomous. For example, some writers have defended a view of autonomous biology, according to which biological science is not reducible to the physical sciences. Vitalism postulated non-physical attributes or vital forces that were supposed to be present in living organisms. More recent neovitalistic positions avoid these postulates, but attempt to give empirical reasons against the feasibility of reducing biology. Other, sometimes a priori, arguments have been given against the reducibility of psychology to physiology and of the social sciences to psychology. These disputes indicate the continuing intellectual significance of the idea of unity of science and the broad range of issues it encompasses.
See also EXPLANATION, PHILOSOPHY OF SCIENCE , PHILOSOPHY OF THE SOCIAL SCI — ENCES , REDUCTIO. R.L.C.