Transfer of concepts and paradigms between disciplines has usually been a fruitful process, but in order to be successful it requires extreme caution; otherwise it could lead to grave misunderstandings, as witnessed e.g. by the transfer of concepts like determinism, local causality, realism and reductionism, from the triumphant 19th century classical physics to the positivist philosophy.

Since then considerable progress has been made in the proper interpretation of the revolutionary developments in physical sciences, including quantum physics and relativity. One would expect hope that this experience would help to resolve similar dilemmas in life sciences, where they are even more pronounced when dealing e.g. with the onset of life and consciousness, at least where the concepts are “borrowed” from physics.

This paper addresses one such important concept – reductionism, which is also connected with the ideas of complexity, emergence, levels of hierarchy or reality, etc.  Reductionism in its different forms has usually been “taken for granted” on the basis of its successful application in physical sciences, but has recently also been critically reassessed. Of course, in its “weakest” (or methodological) form reduction is a legitimate scientific method, but it becomes controversial in its “strong” versions: epistemological (or conceptual), with its constructivist claims, and ontological (or causal), which attributes reality only to the lowest level, with all others being “nothing but” its derivatives. It becomes particularly important to analyse the validity of “strong” reductionism because it is used to justify (recently increasingly aggressive) scientistic claims to ultimate truth.

Recent criticism of “strong” reductionism is coming from a growing group of prominent condensed matter theorists who question the claims of epistemological and ontological reductionism, and especially its constructivist claims, based on evidence coming from their studies of many-body systems. They show that the introduction of new concepts is essential for a successful explanation of the physical phenomena observed at a particular level of complexity. Even the properties of “simple” systems with large number of elements cannot be understood by straightforward application of the laws governing its elements, without introducing new assumptions about the behaviour at this “higher” level. New physical phenomena emerge, determined only by some “higher organizing principle” (e.g. symmetry) and independent of the lower level properties, defining what is called “quantum protectorates”. This also confirms the plurality of levels of reality, contrary to the reductionist attribution of reality only to the lowest level.

Many well-known examples from condensed matter physics confirm this analysis, from the Landau liquid to superconductivity, ferromagnetism, quantum Hall states, but it can also be extended to the higher energy phenomena including the structure of the universe.

This criticism of strong reductionism and evidence for emergent phenomena should also be relevant in the studies of biological systems, but this message is too important to be ignored in other fields of science, as well as in philosophy.