 Whereas the first point of contrast is drawn from the practice of physics, the second is logical. After reducing the system to its parts, the next step in the standard approach to understanding, according to Kellert, is to construct a “deductive scheme, which yields a rigorous proof of the necessity (or expectability) of the situation at hand” (1993, p. 91). What Kellert is referring to, here, is the deductive-nomological account of explanation (see Section 2 of the entry on  scientific explanation, on the DN model). The approach in chaotic dynamics makes no use of deductive inferences. Specifically, instead of looking at basic principles, propositions, and so on, and making deductive inferences, chaos explanations appeal to computer simulations because of the difficulty or even impossibility of deducing the chaotic behavior of the system from the model equations (e.g., no proof of SD for the Lorenz model based on the governing equations). 