Some mechanists argue that the covering law model of constitutive explanation has problems analogous to those that beset the covering-law model of etiological explanations. Action potentials cannot be explained by mere temporal sequences of events utterly irrelevant to the phenomenon, but one can derive a description of the action potential from descriptions of such irrelevant phenomena. Action potentials cannot be explained by mere patterns of correlation that are not indicative of an underlying causal relation. Irrelevant byproducts of a mechanism might be correlated with the behavior of the mechanism, even perfectly correlated such that one could form bridge laws between levels, but would not thereby explain the relationship. Merely finding a neural correlate of consciousness, for example, would not, and is not taken by anyone to, constitute an explanation of consciousness. So mechanists argue that micro-reductive explanations must satisfy causal constraints just as surely as etiological explanations must (Craver 2007).