 In general, Heytesbury introduces three levels of  validity.[22]  First, validity as relevance secured by logical form in every domain of application, explicated as truth-preservation of all inferences sharing the same logical form (forma or modus arguendi) with respect to every imaginable world. Second, validity as relevance secured by conceptual content with a restricted domain of application, explicated as truth-preservation with respect to all imaginable worlds, which is not substitution-invariant. Third, validity as simple truth-preservation with respect to all possible worlds. Heytesbury’s parallel use of different concepts of formality makes him a representative of British logic in the transitional period, containing different stages of development: the substitutional view (validity preserved in all substitution-instances) typical for the “Continental tradition”, the relevance view (conceptual connection) typical for the “British tradition” and later Paul of Venice and Paul of Pergula, and formality as reducibility to a syllogism typical for the early fourteenth-century  tradition.[23]