 How, from perceptible effects, does one arrive at knowledge of the cause? I respond, by dividing thus: in [a situation of type] A are present [factors] B, C, D, if you wish to know which of D, B, or C is a cause, consider the case where you find B without C. If then D follows B and not C, then in [a situation of type] A, B is the cause of D. (Scotus In Met. I qu. 4) 