Reductionism is a concept in philosophy that claims a description of properties in a complex system can be “reduced” to the lower-level properties of the system’s components. For example, the laws and properties of chemistry can be reduced to the laws of physics.
More specifically, the properties of molecules can be reduced to those of atoms, the properties of biological cells can be reduced to those of molecules, plants and animals can be reduced to those of cells, and mind can be reduced to neurons in the brain.
Beyond the properties, reductionists claim that causal laws of nature in the base level must causally determine the laws of a higher level. These thinkers usually have a highly simplistic, materialistic, and deterministic view of the most fundamental laws of nature, namely the laws of classical physics, or the interpretations of quantum physics that deny indeterminism.
Anti-reductionists deny claims that deterministic causal laws can in principle reduce everything, including life and mind, to the fundamental particles of physics. They include emergentists, who think at least some higher level properties and laws cannot be reduced, but must emerge as sui generis entities that need new explanations. They also include vitalists, who believe that a dualistic, non-physical, immaterial substance is needed to explain life, mind, and consciousness.
Information philosophy identifies the transitions from non-life to life as active replication of information structures with immaterial, but physical, information processing, the transition to a free and creative mind as that immaterial information processing, the transition to consciousness as the development of an experience reorder and reproducer (ERR), and the transition to human knowledge (SUM) as the external communication and storage of information in all human artifacts.