Enneads II.7: About Mixture to the Point of Total Penetration
Explanation of Mixture That Occupies More Space Than Its Elements
In the case where the compound occupies more space than each element separately, it might (though with little probability), be asserted, that, since every body, along with its other qualities, implies size, a local extension must take place. No more than the other qualities could this increase perish. Since, out of both qualities, arises a new form, as a compound of the mixture of both qualities; so also must another size arise, the mixture combining the size out of both. Here (the Peripatetics) might answer (the Stoics): "If you assert a juxtaposition of substances, as well as of the masses which possess extension, you are actually adopting our opinions. If however one of the masses, with its former extension, penetrate the entire mass of the other, the extension, instead of increasing, as in the case where one line is added to another by joining their extremities, will not increase any more than when two straight lines are made to coincide by superimposing one on the other."
The case of the mixture of a smaller quantity with a greater one, such as of a large body with a very small one, leads (the Peripatetics) to consider it impossible that the great body should spread in all the parts of the small one. Where the mixture is not evident, the (Peripatetics) might claim that the smaller body does not unite with all the parts of the greater. When however the mixture is evident, they can explain it by the extension of the masses, although it be very doubtful that a small mass would assume so great an extension, especially when we attribute to the composite body a greater extent, without nevertheless admitting its transformation, as when water transforms itself into air.