Distinction between T2- and T3-systems

A T2-system adapts through control mechanisms at two different levels of organizational hierarchy. A mechanism at one level controls the properties of a mechanism at another level. Thus, we may say that the system has two adaptive traverses. The important implication is that a T2-system has an internal structure at which it can store newly acquired knowledge about the world. This structure is the point of interaction between the two traverses: One type of control mechanisms stores the new knowledge while the other uses that knowledge. For example, brain plasticity mechanisms may store knowledge in a form of synaptic weights, while neuronal activity uses these synaptic weights in order to create behavior. Similarly, one set of biological mechanisms may produce a new combination of genes in a genome and another set of mechanisms uses those genes.

A minimum of T2-organization is required for a system to be able to adapt to new circumstances in the surrounding world. A system that has zero or one traverse (T0 or T1) cannot adapt because it cannot inflict changes on itself.

A T3-system has three traverses and is even more adaptive because it has two internal structures for storage of new knowledge. These two structures are organized into a hierarchy. That is, the system can change itself at two different levels of organization. The implication is that a T3-system changes itself not only using fixed cybernetic knowledge on how to make those changes (fixed learning rules), but it also has the option of acquiring cybernetic knowledge on how to more efficiently make changes in the future.

A T2-system has to adjusts to every new change in the environment from scratch because it always adjusts in the same way. It cannot improve its adjustment capabilities through experience. In contrast, a T3-system increases its adjustment capabilities over time. As it acquires more knowledge, a T3-system can more quickly adjust to a new change in the environment, provided that there is a resemblance between the new environmental properties and the environmental properties at some earlier time point to which the system has already once adjusted.

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