On Sense And The Sensible   

impossibility of discerning such concurrent stimuli coinstantaneously.

For we must suppose that the stimuli, when equal, tend alike to efface

one another, since no one [form of stimulus] results from them; while,

if they are unequal, the stronger alone is distinctly perceptible.

Again, the soul would be more likely to perceive

coinstantaneously, with one and the same sensory act, two things in

the same sensory province, such as the Grave and the Sharp in sound;

for the sensory stimulation in this one province is more likely to

be unitemporal than that involving two different provinces, as Sight

and Hearing. But it is impossible to perceive two objects

coinstantaneously in the same sensory act unless they have been mixed,

[when, however, they are no longer two], for their amalgamation

involves their becoming one, and the sensory act related to one object

is itself one, and such act, when one, is, of course,

coinstantaneous with itself. Hence, when things are mixed we of

necessity perceive them coinstantaneously: for we perceive them by a

perception actually one. For an object numerically one means that

which is perceived by a perception actually one, whereas an object

specifically one means that which is perceived by a sensory act

potentially one [i.e. by an energeia of the same sensuous faculty]. If

then the actualized perception is one, it will declare its data to

be one object; they must, therefore, have been mixed. Accordingly,

when they have not been mixed, the actualized perceptions which

perceive them will be two; but [if so, their perception must be

successive not coinstantaneous, for] in one and the same faculty the

perception actualized at any single moment is necessarily one, only

one stimulation or exertion of a single faculty being possible at a

single instant, and in the case supposed here the faculty is one. It

follows, therefore, that we cannot conceive the possibility of

perceiving two distinct objects coinstantaneously with one and the

same sense.

But if it be thus impossible to perceive coinstantaneously two