Jan Pinborg is speaking of late thirteenth- and early fourteenth-century semantics as formulated by the thinkers who are now commonly called modistae because the concept of modi significandi was one of their main tools in analyses of logical and grammatical problems. The particular problem to which Pinborg is referring is that of the meaning of such words as 'white' and 'whiteness' – album and albedo. Pre-modistic writers of the twelfth–thirteenth centuries often describe the semantic difference between aats and cats in terms of different modi significandi, and similarly with substantial abstract and concrete terms. Peter of Auvergne, in the modistic period, gives parallel presentations of modistic approach for substantial and accidental terms. On Boethius's mature view album and albedo have the same denotata, and similarly with 'coloratum' and 'color'. Bacon distinguishes between adjectival and substantival use of album. It may seem strange that most of Bacon's contemporaries neglected the substantive/adjective distinction.