Emergent properties are holistic properties that can not be reduced to a single compositional property and are the product of many different compositional properties combined together (for example the saying that the whole is greater then its parts). Emergent properties do not share a isomorphic -- see Wittgenstein's Tractatus Logico-Philosophicus and related discussions on correspondence theory in philosophy of science -- relationship between their compositional properties. For example consciousness might be viewed as a emergent property because it takes many different parts of the brain (compositional properties) working together to produce any sort of unified experience (holistic property). There are two types of emergent properties: strongly emergent properties and weakly emergent properties (please note that the distinction between weak and strong is not that of my own but the terminology of one of my pervious mentors and colleagues).

A weakly emergent property is such that more then one type of compositional property can give rise to the same holistic property. For example, the qualitative color of red (holistic property) can be produced by different spectral wave frequencies (compositional properties) besides those that are commonly associated with red. A metamer of red would then be a color that has the same qualitative features of the color red but does not have the same compositional properties associated with the color red.

A strongly emergent property is such that one type of compositional property can give rise to what appears to be two distinct holistic properties. For example, being a tricky psychologist I might very well devise a study that is a taste testing challenge between Pepsi and Coke. I would tell the participants in the study that the purpose of the challenge was to see whether or not they could truly tell the difference between what makes Pepsi what it is as opposed to what makes Coke what it is (taste wise, of course). The only difference is that I would essentially lie to the subjects by making both samples that I would give to them containing Pepsi. If a single subject reported that one sample was Coke then we would have evidence that the compositional properties of Pepsi produced within the subject two different holistic properties -- i.e., that of the taste of Coke and that of the taste of Pepsi.

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