 Medieval philosophers explained the significance of general terms by a complex theory of supposition (see Spade 1982). The Logic condenses this framework so that the significance of general ideas has two aspects: the comprehension and the extension. The comprehension consists in the set of attributes essential to the idea. For example, the comprehension of the idea “triangle” includes the attributes extension, shape, three lines, three angles, etc. The extension of the idea consists in the particular objects to which it applies, which includes “all the different species of triangles” (I.6, 39–40). Here the authors confuse matters by trying to incorporate the traditional terms “inferiors” and “species”, taking the latter for individual objects. Usually, however, they straightforwardly take the extension of a general idea to be the individuals possessing the attributes in its comprehension. There are three key features of this theory of signification. First, the comprehension rather than the extension is essential to the function of a general idea: one cannot remove an attribute without destroying it—making it into a different idea, whereas one can restrict its extension by applying it to only some of the objects that fall under it. Second, the comprehension governs the extension: the set of attributes determines the individuals in its extension. Finally, comprehensions and extensions are inversely related. In adding attributes to the comprehension of an idea one restricts its extension. For example, the comprehension of the idea “mammal” includes that of the idea “animal” so the extension of “animal” includes that of “mammal.” The Logic implicitly assumes this principle throughout the text. In recognizing these two modes of the signification of words—both the comprehension of the associated idea and the objects in the extension—it replaces the traditional distinction between incomplete and complete entities in the treatment of the signification of general terms.