 He then precedes to formulate the condition of local causality, which is that a full specification of beables in the overlap of the backward light cones of the spacetime regions 1 and 2 should screen off correlations between them. Implicit in this is that correlations between two variables be susceptible to causal explanation, either via a causal connection between the variables, or via a common cause. This assumption is made explicit in a later article (Bell 1981), in which he says that “the scientific attitude is that correlations cry out for explanation” (Bell 1981, C2–55; 1987b and 2004, 152).