Emergence

The term emergence is used in a variety of (often incompatible) ways in the philosophic and scientific literature. However, emergentism is always a thesis about properties, and most versions share the following components: Emergent properties are (i) dependent upon, (ii) determined by, and (iii) not deducible from, basic physics. A highly diverse range of properties has been held, at various times, and by various philosophers and scientists, to be emergent. Examples include mental properties, most often consciousness; chemical bonding; and ordered patterns such as tornados in chaotic systems such as the weather. To say of such properties that they are emergent is to say something about the way they are related to the particles, properties, and laws of physics. This entry first clarifies the related notions of emergence and nondeducibility, then distinguishes three distinct forms of emergence with respect to the basic physical level. Let us begin with clarification of the key notions.

Emergent properties are

• i.
  instantiated only by complex physical particulars,
• ii.
  determined by structural physical properties of their bearers, and
• iii.
  nondeducible from physics.

Emergentists about the mind, for instance, think that at least some mental properties (e.g., beliefs, desires, sensory experiences) satisfy (i–iii). Focus on this kind of emergence. Component (i) contrasts emergentism with Cartesian substance dualism—emergentists deny any nonphysical mental substance in which our mental lives take place. Mental properties are possessed only by things that are fully composed of physical parts (e.g., brains). Component (ii) holds that instantiation of certain structural physical properties is sufficient for instantiation of emergent properties and entails that you and I cannot differ mentally unless we also differ physically. Components (i) and (ii) are common to most extant theories of mind, emergentist or not, and are often jointly referred to as the supervenience of mental properties on the physical. What distinguishes emergentism from these other positions is component (iii). Nondeducibility makes emergent properties surprising,novel, and unexpected with respect to the physical properties they emerge from—no scientist could deduce your mental state merely from physical knowledge about your brain, body, environment, and so on. The broad consensus on defining emergence in terms of nondeducibility hides significant differences. Just as there are several ways in which you can fail to have blue eyes, so there are several ways in which a property can fail to be deducible from physics.