 In this structure, there are two different causal routes from \(X\) to \(Y\)—a direct causal relationship and an indirect relationship with \(Z\) as an intermediate variable. If \(a = {-bc}\), there is cancellation along these two routes. This means that no intervention on \(X\) will change the value of \(Y\). In one natural sense, this seems to mean that \(X\) does not cause \(Y\), assuming that (C*) a necessary condition for \(X\) to cause \(Y\) is that some interventions on \(X\) are associated with changes in the value of \(Y,\) as an obvious extension of CD seems to suggest. In another natural sense, however, \(X\) does seem to be a cause—indeed a direct cause—of \(Y\). We can resolve this apparent inconsistency by distinguishing between two kinds of causal claims (for a related distinction, see Hitchcock 2001b )—the claim \(X\) is a total or net cause of \(Y\), where this is captured by (C*) and the claim that \(X\) is a direct cause of \(Y\), where this is understood along the following lines: \(X\) is a direct cause of \(Y\) if and only if under some intervention that changes the value of \(X\), the value of \(Y\) changes when all other variables in the system of interest distinct from \(X\) and \(Y\) including those that are on some causal route from \(X\) to \(Y\), are held fixed at some value, also by interventions. (For related, but different, characterizations of direct causation along these lines, see Pearl 2009 and Woodward 2003.) Fixing the other values of other variables means that each of these values is determined by separate processes, each meeting the conditions for an intervention, that are appropriately independent of each other and of the intervention that changes the value of \(X\). The effect of intervening to fix the values of these variables is thus that each variable intervened on is disconnected from its causes, including \(X\). In the example under discussion, \(X\) qualifies as a direct cause of \(Y\) because if we were to fix the value of \(Z\) in a way that disconnects it from the value of \(X\), and then intervene to change the value of \(X\), the value of \(Y\) would change. This idea can then be generalized to provide a characterization of “contributing” causation along a causal route, i.e., to capture the sense in which \(X\) is an indirect cause of \(Y\) along the route that goes through \(Z\) (Woodward 2003).