 No aspect of Hempel’s position generated more controversy than the symmetry thesis, which holds that, for any adequate explanation, had its premises—its initial conditions and covering laws—been taken into account at a suitable prior time, then a deductive prediction of the occurrence of the explanandum event would have been possible, and conversely (Hempel &amp; Oppenheim 1948). Inferences from adequate explanations to potential predictions were generally accepted, but not the converse. Critics, such as Michael Scriven (1962), advanced counter-examples that were based on correlations or “common causes”: the occurrence of a storm might be predicted when cows lie down in their fields, for example, yet their behavior does not explain why the storm occurs. Sylvain Bromberger offered the example of the length of the shadow cast by a flagpole, which is sufficient to deduce the height of the flagpole and thus satisfies Hempel’s conditions but does not explain why the flagpole has that height (Bromberger 1966). Since logical relations are non-temporal, Hempel may have taken the symmetry thesis to be a trivial consequence of his account, but deeper issues are involved here.