A property of a system is said to be emergent if it is in some sense more than the "sum" of the properties of the system's parts. An emergent property is said to be dependent on some more basic properties (and their relationships and configuration), so that it can have no separate existence. However, a degree of independence is also asserted of emergent properties, so that they are not identical to, or reducible to, or predictable from, or deducible from their bases.
A refinement of vitalism
may be recognized in contemporary molecular histology in the proposal
that some key organising and structuring features of organisms, perhaps
including even life itself, are examples of emergent processes;
those in which a complexity arises, out of interacting chemical
processes forming interconnected feedback cycles, that cannot fully be
described in terms of those processes since the system as a whole has
properties that the constituent reactions lack.
John Stuart Mill outlined his version of emergentism in System of Logic (1843). Mill argued that the properties of some physical systems, such as those in which dynamic forces combine to produce simple motions, are subject to a law of nature he called the "Composition of Causes".
According to Mill, emergent properties are not subject to this law, but
instead amount to more than the sums of the properties of their parts.