Life is defined by Maturana and Varela as a type of self-organization: autopoiesis in the physical space. This resembles the concept of metabolism, which itself is typically included in definitions of life. Three senses of metabolism are distinguished. If life depends on either autopoiesis or metabolism (in the third sense), then strong A-Life is impossible. The theory of autopoiesis challenges concepts familiar in biology and cognitive science. While its use of informational language is too restrictive, its use of cognitive language is too liberal: life does not imply cognition.
The autopoietic approach is unusual also in its choice of theoretical vocabulary for describing behaviour. Orthodox biologists, neuroscientists, and most cognitive scientists are happy to speak in terms of function, information processing (including input, output, computation, instruction, translation, execution, and code), representation, and learning. Maturana and Varela use autopoietic arguments to criticize each of these concepts. Although admitting that they can be useful metaphors, they also see them as potentially misleading. They prefer to speak in literal terms of intimately coupled dynamical systems, connected in a continuous process of mutual perturbation.