In the Laws of Thought, Boole abandoned the interpretation of secondary propositions based on the notion of "conjunctures of circumstances' (or in terms of the "uni-verse of cases") as proposed in Mathematical Analysis of Logic,¹ and developed an original semantical theory based upon temporal relations between propositions.² This new approach emphasizes the notion of duration in order to give a temporal interpretation of several propositions and thereby to determine the respective periods of their duration.