 Aristotle identifies continuity and discreteness as attributes applying to the category of  Quantity.[9]  As examples of continuous quantities, or continua, he offers lines, planes, solids (i.e., solid bodies), extensions, movement, time and space; among discrete quantities he includes  number[10]  and  speech.[11]  He also lays down definitions of a number of terms, including continuity. In effect, Aristotle defines continuity as a relation between entities rather than as an attribute appertaining to a single entity; that is to say, he does not provide an explicit definition of the concept of continuum. He observes that a single continuous whole can be brought into existence by “gluing together” two things which have been brought into contact, which suggests that the continuity of a whole should derive from the way its parts join up (see Physics V, 3).  Accordingly for Aristotle quantities such as lines and planes, space and time are continuous by virtue of the fact that their constituent parts “join together at some common boundary” (Catergories, VI [MOMM]).  By contrast no constituent parts of a discrete quantity can possess a common boundary.