  Since a definition does not assert or deny, Aristotle probably intends us to understand definitions as stipulations or as defining expressions which are equivalent in some way to the defined term. The definition of unit as ‘indivisible in quantity’ will not presuppose that units do or do not exist. Hence, the syllogistic premise, ‘A unit is indivisibile in quantity,’ if taken as presupposing the existence of units, will not be a definition in this sense. Later, of course, Aristotle will allow for many other kinds of definitions.