 After careful observations, a scientist in the cubical world notices there are correlations between the shadows on the ceiling and those on the wall. After having repeatedly observed such correlations, the scientist infers the probabilistic hypothesis that there must exist something responsible for the shadows seen on the walls and ceiling. The reasoning leading to that conclusion is nothing other than an inference to a common cause. Although the principle of the common cause (see  § 5.4.1)  was introduced by Reichenbach in The Direction of Time, published posthumously in 1956, and does not appear at all in Experience and Prediction (1938), Salmon conjectured that the idea was already there, as testified by Reichenbach’s tenet that any physicist who happens to repeatedly observe some coincidences “will not believe in a matter of chance but will look for a causal connection” (Reichenbach 1938: 121).