In general, the belief that statements or expressions concerning one level of organization can be replaced by simpler ones at a lower level. In its most radical form, it holds that all matter, both organic and inorganic, is made up of atoms and molecules, and therefore the theories, laws and models applicable to these basic elements adequately explain phenomena at higher levels of organization, without the need for postulating any emergent properties. Thus, the logical (or rather illogical) conclusion was that disciplines such as anthropology, biology, and psychology have no independent existence and therefore can be abolished. Assumed in the past to provide the basis for achieving the unity of science and requiring the use of bridge laws in its more sophisticated application, this form of reductionism (termed ‘greedy’ reductionism by Daniel C. Dennett) was opposed by holism. Reductionism can also involve the standpoint that the behavior of complex systems can be understood by analyzing its constituent parts. These examples serve to point out that reductionism can assume a number of different types, which are summarized in the table below. Reductionism of one type or other continues to impinge on the relationship between neuroscience and psychology in terms of whether brain and mind are two aspects of a single event, one described in the language of ‘biochemese’ (or ‘neurogenese’) and the other in ‘psychologese’. Thus, taking an example from Steven Rose, it might be held that memory failure is caused by the action of inhibitory protein synthesis. These terms, however, are two names for the same phenomenon, but the language differs and therefore the problem is to translate between the two languages (e.g., by means of analogies in the first instance). Consequently, the relationships between levels are not causal, but one of mapping one level onto the other (i.e., an isomorphism between descriptions of events and processes in the language of, for example, biochemistry and psychology). The point is, according to Rose, that all psychological phenomena are potentially translatable into biochemistry, but not all biochemical activity translates into psychology.
| Type | Description | Comments |
| Ontological
reductionism |
Everything in existence consists of a small number of basic substances that behave in a regular way1 | Similar to monism, an approach to mind-body problem |
| Methodological reductionism | 1. Explanations of things, including scientific ones, need to be reduced to the simplest possible entities
2. Application of methods or techniques from one discipline (e.g., physics) to another (e.g., psychology2 |
1. Similar to Ockham’s razor or the principle of ontological economy
2. In the case of statistical techniques, quantum mechanics has had an important influence on the study of human behavior: it is acknowledged not only to be deterministic, but also stochastic |
| Theoretical
reductionism (TR) |
1. In its most extreme form, it holds that one theory can come to replace another4
2. While older theories or explanations might not be replaced outright by newer ones, new theories can be refinements or reductions of the old theory in greater detail |
In modern science at least, this has rarely happened. According to Patricia Churchland (1986)3, it is rather a case of one theory displacing another (e.g., Newtonian mechanics was largely displaced, but not replaced, by Einstein’s special theory of relativity in physics). This version of TR also holds that laws of one theory can be deduced from those of another
2. If not replaced or displaced, the older theories may be re-worked by a new one to account for perceived discrepancies that reveal shortcomings in explanatory power. Examples include some of the original information-processing theories in psychology |
| Linguistic
reductionism |
Everything can be described in a language with a limited number of core concepts and combinations of them | Another version of Ockham’s razor and a goal of the logical positivists |
| Scientific
reductionism |
Used to denote all of the above, but also to covey the claim that all phenomena can be reduced to scientific explanations | Sometimes taken to include causal reductionism: the causes of one thing are completely explainable in terms of the existence of causes of another thing4 |