The concept of emergence is a very old idea, dating at least to the nineteenth century, with some hints of it in ancient and medieval philosophy (Parmenides, Empedocles, Democritus, Aristotle). Emergence is a phenomenon whereby larger entities arise through interactions among smaller or simpler entities such that the larger entities exhibit properties the smaller/simpler entities do not exhibit.

A termite "cathedral" mound produced by a termite colony offers a classic example of emergence in nature.

Ripple patterns in a sand dune created by wind or water is an example of an emergent structure in nature.

In other words, there can be properties - perhaps even “laws” - at the upper hierarchical levels of nature that are not derivable from or reducible to the properties and laws of the lower levels: Chemistry has properties not derivable from physics, biology properties not derivable from chemistry, and psychology properties not derivable from biology.

Reductionism, by contrast, argues that everything can be explained by (reduced to) the basic laws of physics. The world is said to be causally closed. 1) The simple reference to this principle, along with the assumption that mental properties are not reducible to physical properties, are all that's needed to set the Problem of Exclusion argument in the problem of mental causation in motion.

Contemporary approaches to the mind typically work within the framework of physicalism, the view that everything that exists in space-time is exclusively physical or constituted by the physical; the idea that everything that is caused has a physical cause. Usually this is taken to mean that deterministic physical laws will eventually be found that explain everything. Even if there were an indeterministic “uncaused” cause (a causa sui, something which is generated within itself), it would still be a physical cause.

While the original mind-body problem was simply the puzzle of how an immaterial mind could cause a material body to move, lately the problem of mental causation has been recast as the logical resolution of one basic premise and a conclusion, which we might call the standard argument against mental causation:

  • The only causes are physical causes. (These causes need not be deterministic. An indeterministic quantum statistical event gives us the probabilities for subsequent events, “causing” them in a way that is not pre-determined.)
  • Therefore, mental events cannot cause physical events.

What if there is a hierarchy of levels of organizational complexity of material particles that includes, in ascending order, the strictly physical, the chemical, the biological, and the psychological level? Upper hierarchical levels have the power to influence motion in ways unanticipated by laws governing less complex kinds and conditions concerning the arrangements of particles. Emergentism is committed to the lawlike possibility of what has been called “downward causation,” control by an upper level of the component particles of the lower levels. We can now demonstrate that this is actually realized in biological systems.

The informational analysis of non-reductive physicalism must show exactly how information does not move in the upward direction between hierarchical levels (fundamentally because noise in the lower level makes motions incoherent), but that information does move down as the higher-level information-processing system uses it to manipulate individual physical particles (maintaining a high signal-to-noise ratio in the upper level).