Strong emergence is a type of emergence in which the emergent property is irreducible to its individual constituents. Some philosophers have proposed that qualia and consciousness demonstrate strong emergence. Strong emergence stands in contrast to weak emergence.
Strong emergence says that if systems can have qualities not directly traceable to the system's components, but rather to how those components interact, and one is willing to accept that a system supervenes on its components, then it is difficult to account for an emergent property's cause. These new qualities are irreducible to the system's constituent parts.(Laughlin 2005) The whole is greater than the sum of its parts. This view of emergence is called strong emergence. Strong emergence is a view not widely held in the physical sciences but proposed as a philosophical theory of etiology, epistemology and ontology.
However, "the debate about whether or not the whole can be predicted from the properties of the parts misses the point. Wholes produce unique combined effects, but many of these effects may be co-determined by the context and the interactions between the whole and its environment(s)." Along that same thought, Arthur Koestler stated, "it is the synergistic effects produced by wholes that are the very cause of the evolution of complexity in nature" and used the metaphor of Janus to illustrate how the two perspectives (strong or holistic vs. weak or reductionistic) should be treated as perspectives, not exclusives, and should work together to address the issues of emergence. Further,
The plausibility of strong emergence is questioned by some as contravening our usual understanding of physics. Mark A. Bedau observes:
One must make a distinction between a) macroscopic properties (e.g. superconductivity) which nobody has, as a matter of fact, been able to deduce from the microscopic equations and b) the idea that something macroscopic has features that are not even due to microscopic interactions. Laughlin belongs to a). In his book, he explains that for many particle systems, nothing can be calculated exactly from the microscopic equations, and that macroscopic systems are characterised by broken symmetry: the symmetry present in the microscopic equations is not present in the macroscopic system, due to phase transitions. As a result, these macroscopic systems are described in their own terminology, and have properties that do not depend on many microscopic details. This does not mean that the microscopic interactions are irrelevant, but simply that you do not see them anymore - you only see a renormalized effect of them. Laughlin is a pragmatic theoretical physicist: if you cannot, possibly ever, calculate the broken symmetry macroscopic properties from the microscopic equations, then what is the point of talking about reducibility?