 It is often assumed that each of the structural equations in the system is independently disruptable. For instance: there is, at least in principle, some way of disrupting \(C\)’s causal influence on \(D\)—some way of making it so that the structural equation \(D \coloneqq C\) no longer holds—which leaves it so that both of the structural equations \(A\coloneqq B \wedge \neg C\) and \(E\coloneqq A \vee D\) continue to hold. Not every way of disrupting the causal relation between the variables \(C\) and \(D\) will be like this. For instance, suppose that we remove all of the connections emanating out of the neuron c. This will disrupt the causal connection between \(C\) and \(D\), but it will also disrupt the causal connection between \(C\) and \(A\); it will make it so that the structural equation \(A\coloneqq B \wedge \neg C\) no longer holds. (This equation tells us that, if \(C=1\), then \(A=0\); but, with the connection between c and a severed, this is no longer true.) This property of a system of structural equations—that each of the equations may be disrupted without affecting any of the other equations in the model—is known as modularity. (For criticism of this requirement, see Cartwright 2002; for a defense, see Hausman &amp; Woodward 1999, 2004. For more on modularity, see Woodward 2003.)