 It is worth adding that although this appeal to combinations of interventions may seem artificial, it maps on to standard experimental procedures in an intuitive way. Consider a case of genetic redundancy—gene complex \(G_1\) is involved in causing phenotypic trait \(P\) but if \(G_1\) is inactivated another gene complex \(G_2\) (which is inactive when \(G_1\) is active) will become active and will cause \(P\). The geneticist may test for this possibility by, first, intervening on \(G_2\) so that it is fixed at the value = inactive, then intervening to vary \(G_1\) and observing whether there is a corresponding change in \(P\). Second, the investigator may intervene to render \(G_1\) inactive and then, independently of this intervening to change \(G_2\) and observing whether there is a change in \(P\). As this example illustrates, we may think of different complex causal structures in which there are multiple pathways, redundancy, cancellation and so on, as encoding different sets of claims about what will happen under various possible combinations of interventions.