 Violations of FC are often detectable in principle. For example, suppose that the true causal structure is that shown in  Figure 7,  and that the probability distribution over X, Y, and Z exhibits all of the conditional independence relations required by MC. Suppose, moreover, that X and Z are independent, conditional upon Y. This conditional independence relation is not entailed by MC, so it constitutes a violation of FC. It turns out that there is no DAG that is faithful to this probability distribution. This tips us off that there is a violation of FC. While we will not be able to infer the correct causal structure, we will at least avoid inferring an incorrect one in this case. For details, see Steel 2006, Zhang &amp; Spirtes 2008, and Zhang 2013b.