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[citation needed] 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)."[1] 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.[2]