  Thomas of Erfurt was the most influential member of a group of later medieval philosophers known as the speculative grammarians or Modistae (Modists), after the central place they assigned to the modi significandi (modes of signification) of a word in their analyses of human discourse. The notion that a word, once it has been imposed to signify, carries with it all of its syntactical modes, or possible combinations with other words, had been around since the twelfth century. What the Modistae did was to posit the origins of the modi significandi in terms of parallel theories of modi intelligendi (modes of understanding) and modi essendi (modes of being). The result was a curious amalgam of philosophy, grammar, and linguistics. Thomas of Erfurt's De modis significandi became the standard Modist textbook in the fourteenth century, though it has since enjoyed even greater fame later thanks to its misidentification as a work of Duns Scotus. The text appeared in early printed editions of Scotus's Opera Omnia, where it was read and commented upon by later figures such as Charles S. Peirce and Martin Heidegger, whose 1916 doctoral thesis, Die Kategorien- und Bedeutungslehre des Duns Scotus, should have been titled, Die Kategorienlehre des Duns Scotus und die Bedeutungslehre des Thomas von Erfurt.