An emergent property was a phenomenon in which individual components came together to form a complex system which could only be described as a function of the components acting together, not as a strict addition of the individual components. Emergence was described this way in an exchange between Lieutenant Commander Data and Lieutenant Commander La Forge:

"Complex systems can sometimes behave in ways that are entirely unpredictable. The Human brain for example, might be described in terms of cellular functions and neurochemical interactions. That description does not explain Human consciousness, a capacity that far exceeds neural functions. Consciousness is an emergent property." - Data
"In other words, something that's more then the sum of its parts." - La Forge (TNG: "Emergence")

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