in contact. This entails the possibility of union and separation. Yet this would hold only if, after changing through separation and contact, they remained alike. That is not the case. Rather, when the parts of a united essence separate, the parts change: after separation, they no longer remain as they were when united. This is observable in created bodies: their parts’ union with one another gives them strength and other attributes that are absent when they are separated. Indeed, some properties of these parts, and of the essence of which they form parts, can hold only when they are united; separation nullifies them. Since separation makes them cease to be as they were when united, their likeness does not entail the possibility of their separation, because separation would make them cease to be alike. The supposition would thus amount to saying: if they are alike, they must become unlike.

This is further established by the twelfth argument: every composite body comprises indivisible atoms, as stated, and these are alike, as stated. Whatever is possible for either of two like things is possible for the other. We therefore say: when these parts separate, either they remain as they were when united, or they do not. If they do, it follows that, for every body in the world whose parts are separated into indivisible atoms, the state of those atoms when they were connected and constituted that essence must be the same as their state when separated. Yet the falsity of this is evident through sense perception and self-evident knowledge, for