another question respecting sense-perception is as follows: assuming, as is natural, that of two [simultaneous] sensory stimuli the stronger always tends to extrude the weaker [from consciousness], is it conceivable or not that one should be able to discern two objects coinstantaneously in the same individual time? the above assumption explains why persons do not perceive what is brought before their eyes, if they are at the time deep in thought, or in a fright, or listening to some loud noise. this assumption, then, must be made, and also the following: that it is easier to discern each object of sense when in its simple form than when an ingredient in a mixture; easier, for example, to discern wine when neat than when blended, and so also honey, and [in other provinces] a colour, or to discern the nete by itself alone, than [when sounded with the hypate] in the octave; the reason being that component elements tend to efface [the distinctive characteristics of] one another. such is the effect [on one another] of all ingredients of which, when compounded, some one thing is formed.

if, then, the greater stimulus tends to expel the less, it necessarily follows that, when they concur, this greater should itself too be less distinctly perceptible than if it were alone, since the less by blending with it has removed some of its individuality, according to our assumption that simple objects are in all cases more distinctly perceptible.

now, if the two stimuli are equal but heterogeneous, no perception of either will ensue; they will alike efface one another’s characteristics. but in such a case the perception of either stimulus in its simple form is impossible. hence either there will then be no sense-perception at all, or there will be a perception compounded of both and differing from either. the latter is what actually seems to result from ingredients blended together, whatever may be the compound in which they are so mixed.

since, then, from some concurrent [sensory stimuli] a resultant object is produced, while from others no such resultant is produced, and of the latter sort are those things which belong to different sense provinces (for only those things are capable of mixture whose extremes are contraries, and no one compound can be formed from, e.g. white and sharp, except indirectly, i.e. not as a concord is formed of sharp and grave); there follows logically the 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 objects in the same province of sense if they are really two, manifestly it is still less conceivable that we should perceive coinstantaneously objects in two different sensory provinces, as white and sweet. for it appears that when the soul predicates numerical unity it does so in virtue of nothing else than such coinstantaneous perception [of one object, in one instant, by one energeia]: while it predicates specific unity in virtue of [the unity of] the discriminating faculty of sense together with [the unity of] the mode in which this operates. what i mean, for example, is this; the same sense no doubt discerns white and black, [which are hence generically one] though specifically different from one another, and so, too, a faculty of sense self-identical, but different from the former, discerns sweet and bitter; but while both these faculties differ from one another [and each from itself] in their modes of discerning either of their respective contraries, yet in perceiving the co-ordinates in each province they proceed in manners analogous to one another; for instance, as taste perceives sweet, so sight perceives white; and as the latter perceives black, so the former perceives bitter.

again, if the stimuli of sense derived from contraries are themselves contrary, and if contraries cannot be conceived as subsisting together in the same individual subject, and if contraries, e.g. sweet and bitter, come under one and the same sense-faculty, we must conclude that it is impossible to discern them coinstantaneously. it is likewise clearly impossible so to discern such homogeneous sensibles as are not [indeed] contrary, [but are yet of different species]. for these are, [in the sphere of colour, for instance], classed some with white, others with black, and so it is, likewise, in the other provinces of sense; for example, of savours, some are classed with sweet, and others with bitter. nor can one discern the components in compounds coinstantaneously (for these are ratios of contraries, as e.g. the octave or the fifth); unless, indeed, on condition of perceiving them as one. for thus, and not otherwise, the ratios of the extreme sounds are compounded into one ratio: since we should have together the ratio, on the one hand, of many to few or of odd to even, on the other, that of few to many or of even to odd [and these, to be perceived together, must be unified].

if, then, the sensibles denominated co-ordinates though in different provinces of sense (e.g. i call sweet and white co-ordinates though in different provinces) stand yet more aloof, and differ more, from one another than do any sensibles in the same province; while sweet differs from white even more than black does from white, it is still less conceivable that one should discern them [viz. sensibles in different sensory provinces whether co-ordinates or not] coinstantaneously than sensibles which are in the same province. therefore, if coinstantaneous perception of the latter be impossible, that of the former is a fortiori impossible.

some of the writers who treat of concords assert that the sounds combined in these do not reach us simultaneously, but only appear to do so, their real successiveness being unnoticed whenever the time it involves is [so small as to be] imperceptible. is this true or not? one might perhaps, following this up, go so far as to say that even the current opinion that one sees and hears coinstantaneously is due merely to the fact that the intervals of time [between the really successive perceptions of sight and hearing] escape observation. but this can scarcely be true, nor is it conceivable that any portion of time should be [absolutely] imperceptible, or that any should be absolutely unnoticeable; the truth being that it is possible to perceive every instant of time. [this is so]; because, if it is inconceivable that a person should, while perceiving himself or aught else in a continuous time, be at any instant unaware of his own existence; while, obviously, the assumption, that there is in the time-continuum a time so small as to be absolutely imperceptible, carries the implication that a person would, during such time, be unaware of his own existence, as well as of his seeing and perceiving; [this assumption must be false].

again, if there is any magnitude, whether time or thing, absolutely imperceptible owing to its smallness, it follows that there would not be either a thing which one perceives, or a time in which one perceives it, unless in the sense that in some part of the given time he sees some part of the given thing. for [let there be a line ab, divided into two parts at g, and let this line represent a whole object and a corresponding whole time. now,] if one sees the whole line, and perceives it during a time which forms one and the same continuum, only in the sense that he does so in some portion of this time, let us suppose the part gb, representing a time in which by supposition he was perceiving nothing, cut off from the whole. well, then, he perceives in a certain part [viz. in the remainder] of the time, or perceives a part [viz. the remainder] of the line, after the fashion in which one sees the whole earth by seeing some given part of it, or walks in a year by walking in some given part of the year. but [by hypothesis] in the part bg he perceives nothing: therefore, in fact, he is said to perceive the whole object and during the whole time simply because he perceives [some part of the object] in some part of the time ab. but the same argument holds also in the case of ag [the remainder, regarded in its turn as a whole]; for it will be found [on this theory of vacant times and imperceptible magnitudes] that one always perceives only in some part of a given whole time, and perceives only some part of a whole magnitude, and that it is impossible to perceive any [really] whole [object in a really whole time; a conclusion which is absurd, as it would logically annihilate the perception of both objects and time].

therefore we must conclude that all magnitudes are perceptible, but their actual dimensions do not present themselves immediately in their presentation as objects. one sees the sun, or a four-cubit rod at a distance, as a magnitude, but their exact dimensions are not given in their visual presentation: nay, at times an object of sight appears indivisible, but [vision like other special senses, is fallible respecting ‘common sensibles’, e.g. magnitude, and] nothing that one sees is really indivisible. the reason of this has been previously explained. it is clear then, from the above arguments, that no portion of time is imperceptible.

but we must here return to the question proposed above for discussion, whether it is possible or impossible to perceive several objects coinstantaneously; by ‘coinstantaneously’ i mean perceiving the several objects in a time one and indivisible relatively to one another, i.e. indivisible in a sense consistent with its being all a continuum.

first, then, is it conceivable that one should perceive the different things coinstantaneously, but each with a different part of the soul? or [must we object] that, in the first place, to begin with the objects of one and the same sense, e.g. sight, if we assume it [the soul qua exercising sight] to perceive one colour with one part, and another colour with a different part, it will have a plurality of parts the same in species, [as they must be,] since the objects which it thus perceives fall within the same genus?

should any one [to illustrate how the soul might have in it two different parts specifically identical, each directed to a set of aistheta the same in genus with that to which the other is directed] urge that, as there are two eyes, so there may be in the soul something analogous, [the reply is] that of the eyes, doubtless, some one organ is formed, and hence their actualization in perception is one; but if this is so in the soul, then, in so far as what is formed of both [i.e. of any two specifically identical parts as assumed] is one, the true perceiving subject also will be one, [and the contradictory of the above hypothesis (of different parts of soul remaining engaged in simultaneous perception with one sense) is what emerges from the analogy]; while if the two parts of soul remain separate, the analogy of the eyes will fail, [for of these some one is really formed].

furthermore, [on the supposition of the need of different parts of soul, co-operating in each sense, to discern different objects coinstantaneously], the senses will be each at the same time one and many, as if we should say that they were each a set of diverse sciences; for neither will an ‘activity’ exist without its proper faculty, nor without activity will there be sensation.

but if the soul does not, in the way suggested [i.e. with different parts of itself acting simultaneously], perceive in one and the same individual time sensibles of the same sense, a fortiori it is not thus that it perceives sensibles of different senses. for it is, as already stated, more conceivable that it should perceive a plurality of the former together in this way than a plurality of heterogeneous objects.

if then, as is the fact, the soul with one part perceives sweet, with another, white, either that which results from these is some one part, or else there is no such one resultant. but there must be such an one, inasmuch as the general faculty of sense-perception is one. what one object, then, does that one faculty [when perceiving an object, e.g. as both white and sweet] perceive? [none]; for assuredly no one object arises by composition of these [heterogeneous objects, such as white and sweet]. we must conclude, therefore, that there is, as has been stated before, some one faculty in the soul with which the latter perceives all its percepts, though it perceives each different genus of sensibles through a different organ.

may we not, then, conceive this faculty which perceives white and sweet to be one qua indivisible [sc. qua combining its different simultaneous objects] in its actualization, but different, when it has become divisible [sc. qua distinguishing its different simultaneous objects] in its actualization?

or is what occurs in the case of the perceiving soul conceivably analogous to what holds true in that of the things themselves? for the same numerically one thing is white and sweet, and has many other qualities, [while its numerical oneness is not thereby prejudiced] if the fact is not that the qualities are really separable in the object from one another, but that the being of each quality is different [from that of every other]. in the same way therefore we must assume also, in the case of the soul, that the faculty of perception in general is in itself numerically one and the same, but different [differentiated] in its being; different, that is to say, in genus as regards some of its objects, in species as regards others. hence too, we may conclude that one can perceive [numerically different objects] coinstantaneously with a faculty which is numerically one and the same, but not the same in its relationship [sc. according as the objects to which it is directed are not the same].

that every sensible object is a magnitude, and that nothing which it is possible to perceive is indivisible, may be thus shown. the distance whence an object could not be seen is indeterminate, but that whence it is visible is determinate. we may say the same of the objects of smelling and hearing, and of all sensibles not discerned by actual contact. now, there is, in the interval of distance, some extreme place, the last from which the object is invisible, and the first from which it is visible. this place, beyond which if the object be one cannot perceive it, while if the object be on the hither side one must perceive it, is, i presume, itself necessarily indivisible. therefore, if any sensible object be indivisible, such object, if set in the said extreme place whence imperceptibility ends and perceptibility begins, will have to be both visible and invisible their objects, whether regarded in general or at the same time; but this is impossible.

this concludes our survey of the characteristics of the organs of sense-perception and their objects, whether regarded in general or in relation to each organ. of the remaining subjects, we must first consider that of memory and remembering.