The Science of Conjecture: Evidence and Probability Before Pascal

by James Franklin

Suarez’ main contribution to theory was a clear distinction between negative and positive doubt. Doubt is negative when there are no reasons for either side, positive when there are reasons but there is some balance between them. The distinction is relevant to Suarez’ treatment of the case of common soldiers in doubt whether the war of their prince is just: “If the doubt is purely negative, it is more probable that they can go to war, without examining the fact, and leaving the whole burden to the Prince to whom they are subject; whom however I suppose to be of good reputation among all. This is clearly taught by Vitoria and agreed to by all Thomists. But if the doubt is positive, and there are probable reasons on either side, I believe they are perhaps obliged to inquire into the truth. If they cannot arrive at that, they should follow what is more probable, and aid him who more probably is in the right; for when there is doubt on a matter of fact, and one which concerns the harm of our neighbour or the defence of the innocent, one must follow what appears more probable.”