ture of the eye or the ear is in any sense the cause of sight and hearing he seems hardly to be aware" (Dialogues of Plato III. p. 581). In part no doubt the same defect appears in Aristotle. But the descriptions of the eye and ear in Aristotle's writings shew an amount of accurate observation which we look for in vain in Plato.

Defective however as Plato is on the analytic and physiological side, there is another respect in which he far surpasses Aristotle. The organs of sense, Plato is particular to note, are not as perceptive merely mechanical and disconnected members of our body. "No one," he remarks in the Theaetetus," can suppose that we are Trojan horses, in whom are perched several unconnected senses, not meeting in some one nature, of which they are the instruments, whether you term this soul or not, with which through these we perceive objects of sense1" (Jowett's Translation). But of such a reference to soul or mind there is directly but little mention in Aristotle's explanation. The description of the sensitive capacities as themselves a soul, the identification of the different aloŋrýpia with a so-called yuxǹ aloonTin would almost seem to have blinded Aristotle to the insufficiency of mere physical processes to explain a psychological result. His account therefore of the special senses leaves untouched a number of problems which the perceptive processes immediately involve. It is different when our philosopher leaves the physical aspect of the senses, and proceeds to discuss the mode in which the perceptive organs act in concert as a cognitive whole. His results are then of no mere antiquarian interest: the problems which he investigates are those with which we still are occupied. How do our sensations of qualities-white, sweet, &c.—give us knowledge of concrete things? How do we distinguish between the reports of one sensation and those of another? How is it that our sensations sometimes deceive us? how does this complexity of organs, some of which are even double, unite itself into

1 Theaetet. p. 184 D, δεινὸν γάρ που εἰ πολλαί τινες ἐν ἡμῖν, ὥσπερ ἐν δουρείοις ἵπποις, αἰσθήσεις ἐγκάθηνται, ἀλλὰ μὴ εἰς μίαν τινὰ ἰδέαν, εἴτε ψυχὴν εἴτε ὅ τι δεῖ καλεῖν, πάντα ταῦτα ξυντείνει, ᾗ διὰ τούτων οἷον ὀργάνων αἰσθανόμεθα ὅσα αἰσθητά.

one single perception? and what is the character of that mysterious consciousness which accompanies us in our perceptive acts? Such are some of the questions which Aristotle now proceeds to investigate. He solves them, through the doctrine of a common or central sense (kowǹ aïoenois) in which our separate sensations are collected, arranged, and classified.

IX. COMMON OR CENTRAL SENSE.

The particular senses-sight, smell, hearing and the restare all, we have already seen, restricted to some individual quality (idov alonτóv) which can only be perceived by the sense adapted to it. Thus sight takes account only of the colour of objects, smell only of their odour, while touch restricts itself to the hardness or softness, the heat or coldness of external objects. But these single senses as such never really constitute the act of sense-perception. Such perception is not merely a matter of the outward organ: perception is a movement of the mind through the body: and it is only by reference. to this unity of all the senses in a common mental faculty that sense-perception can take place. Without relation to this superior faculty-this Kúpρiov alobητýpiov-no one of the single senses would be fitted for perception. The need of such a central sense of a perceptive faculty which stands to each one of the separate senses as the mind in general stands to each one of its four faculties-is apparent from the mere duplicity which marks the organs of sensation. For just as the body is throughout twofold, so also each of the senses, if we except the touch and taste, appears as a double faculty1, and yet notwithstanding our two eyes, two ears, two nostrils, we still perceive but one colour, one sound, one odour.

This central sense, of which the general nature has been thus far sketched, plays two main functions in relation to the work of

1 De Part. An. 63632; 669b18.

sense-perception. On the one hand, it is required for the distinction and the comparison of the separate communications of the single senses: on the other hand, it is the means by which a consciousness of sensation accompanies the work of sense-perception'.

I. The distinction of our separate sensations. Each single sense, we have already seen, perceives nothing but one single quality or group of qualities. How then is it that we distinguish between the qualities, whether they belong to one and the same sense or be communicated by different senses? The second case constitutes of course the more perplexing question of the two, and is therefore the form in which the problem is generally stated by Aristotle'. What, he asks, is the faculty which distinguishes between white and sweet? The sense of taste communicates to us the feeling of a flavour which is sweet, the sense of eyesight reveals to us the quality of white. But the sense of taste knows nothing of the sensations of sight, the sense which perceives colour knows nothing of the character of flavour. Yet none the less the distinction is there: we not only distinguish white from black, sweet from bitter, but we also separate between the sensation of white and the simultaneous sensation of sweet. Here then two things require to be at once united and disunited, connected and disconnected: they must be subjected to an act of comparison and judged different in consequence of this comparison.

A discrimination of this kind cannot be made by two separate faculties: it is to one single faculty that the two separate

1

111. 2. 10, 426012, ἐπεὶ δὲ καὶ τὸ λευκὸν καὶ τὸ γλυκὺ καὶ ἕκαστον τῶν αἰσθητῶν πρὸς ἕκαστον κρίνομεν, τίνι καὶ αἰσθανόμεθα ὅτι διαφέρει; ἀνάγκη δὴ αἰσθήσει· αἰσθητὰ yap éσTW. Cp. 111. 7. 4, 43120; De Sensu, c. 7. De Somno, 2, 45515, OTL δέ τις καὶ κοινὴ δύναμις ἀκολουθοῦσα πάσαις, ᾗ καὶ ὅτι ὁρᾷ καὶ ἀκούει [omit καὶ with Ε] αἰσθάνεται· οὐ γὰρ δὴ τῇ γε ὄψει ὁρᾷ ὅτι ὁρᾷ. καὶ κρίνει δὴ καὶ δύναται κρίνειν ὅτι ἕτερα τὰ γλυκέα τῶν λευκῶν, οὔτε γεύσει οὔτε ὄψει οὔτ ̓ ἀμφοῖν, ἀλλά τινι κοινῷ μορίῳ τῶν αἰσθητηρίων ἁπάντων.

2 ΙΙΙ. 7, 431324, τί γὰρ διαφέρει τὸ ἀπορεῖν πῶς τὰ μὴ ὁμογενὴ κρίνει ἢ τἀναντία οἷον λευκὸν καὶ μέλαν;

sensations must be transmitted in order that they may be compared and separated'. The case therefore is well compared by Aristotle to what would happen in the case of two opinions between which it was necessary to distinguish. "Were I to perceive one thing, you to perceive another, a third person would be needed to pass judgment on the two." There is required then some one function of the mind by means of which it gains perception of all objects3-some common central organ of perception in which the separate communications of the senses are combined. But how, asks Aristotle, can this central faculty manifest such contrary action as it would seem necessarily to involve? It must take cognizance of two separate sensations and yet meanwhile it must preserve that unity which can alone compare two different sensations: it must within one and the same moment of time present before itself two or more reports of sense. The same thing cannot, it might be thought, move at one and the same time in two opposite directions as undivided and within an undivided space of time. But there is a distinction by the help of which the difficulty may be met. In place, in time and in number, the faculty in question is, we may say, one and indivisible: but in the nature of its action, in its use and application (7 eiva) it is different. Physical analogies may help us further to comprehend this double and apparently contrary action on the part of central sense. We may compare it to the point, taken in its widest sense and understood of either time or space. Such a point is at once one and two:

1 · 426017, οὔτε δὴ κεχωρισμένοις ἐνδέχεται κρίνειν ὅτι ἕτερον τὸ γλυκὺ τοῦ λευκοῦ, ἀλλὰ δεῖ ἑνί τινι ἄμφω δῆλα εἶναι.

* 416 19, οὕτω μὲν γὰρ κἂν εἰ τοῦ μὲν ἐγὼ τοῦ δὲ σὺ αἴσθοιο, δῆλον ἂν εἴη ὅτι ἕτερα ἀλλήλων. δεῖ δὲ τὸ ἓν λέγειν ὅτι ἕτερον.

3 De Sensu, 7, 4498, ἀνάγκη ἄρα ἔν τι εἶναι τῆς ψυχῆς ᾧ ἅπαντα αἰσθάνεται.

4 426022, ὅτι μὲν οὖν οὐχ οἷον τε κεχωρισμένοις κρίνειν τὰ κεχωρισμένα, δῆλον...... ἀλλὰ μὴν ἀδύνατον ἅμα τὰς ἐναντίας κινήσεις κινεῖσθαι τὸ αὐτὸ ᾗ αδιαίρετον καὶ ἐν αδιαιρέτῳ χρόνῳ.

5

42784, τῷ εἶναι μὲν γὰρ διαιρετόν, τόπῳ δὲ καὶ ἀριθμῷ ἀδιαίρετον. De Sensu, Το 449 19, αἰσθάνοιτ' ἂν ἅμα τῷ αὐτῷ καὶ ἑνί, λόγῳ δ ̓ οὐ τῷ αὐτῷ.

* De An. 111. 2, 427 10, ἀλλ ̓ ὥσπερ ἣν καλοῦσί τινες στιγμὴν ᾖ μία καὶ ᾗ δύο,

it is an undivided unit complete within itself, and yet this point can be at once the end of one line and the beginning of another -the same point, that is to say, can be regarded as both one and two it may exist both as divided and as undivided. Or indeed the question-how can this central faculty embrace two contrary qualities and yet not lose its characteristic unity is only the same problem as presents itself when we consider how one and the same object is at once white and sweet: the co-existence of the objective qualities is no less inexplicable than the co-existence in the mind of their subjective counterparts'. In the one case and in the other we must conclude that that which is essentially one can yet manifest itself in two directions: or, in other words, what is marked numerically and locally by unity may yet be conceived of as different.

This exercise of comparison which Aristotle thus assigns to the central or the common sense is not however restricted to the work of distinguishing the separate communications of the senses it displays further its synthetic power in grasping the common properties which are involved in the existence of the qualities of the body. For at the same time as we perceive (say) a colour, we perceive it further as a coloured surface or magnitude: at the same time as we have the sensation of notes

ταύτῃ καὶ διαιρετή. Cp. 111. 7. 4, 431921, ἔστι γὰρ ἔν τι· οὕτω δὲ καὶ ὡς ὄρος. The OTYun in question is to be taken in its most general sense as referring either to time or space. Brentano's interpretation of it as = vv is supported by De Coelo, 111. 1, 300414, τὸ γὰρ νῦν τὸ ἄτομον οἷον στιγμὴ γραμμῆς ἐστιν: but any such definite interpretation is unnecessary, especially as Aristotle, among the synonyms he uses, nowhere speaks of a 'now,' but always of a point or limit. The ordinary sense of point is indeed all that is required. v. Phys. IV. 11, 220a10, kai yàp ǹ otɩjuǹ kai ovvéXEL TÒ μῆκος καὶ ὁρίζει· ἔστι γὰρ τοῦ μὲν ἀρχὴ τοῦ δὲ τελευτή.

1 De Sensu, 7, 449 13, ἢ ὥσπερ ἐπὶ τῶν πραγμάτων αὐτῶν ἐνδέχεται, οὕτω καὶ ἐπὶ τῆς ψυχῆς.

2 De An. III. 1, 425a15, where the koiva are described as those ŵv éкáoτŋ aiono El αἰσθανόμεθα κατά συμβεβηκός. This is generally thought to be in contradiction with 425327, but I have tried to translate the whole passage in such a way as will make the two places quite consistent. (Cp. Bäumker, p. 63.) So also in III. 3. 12, 428b23, the κοῖνα are identified with ἑπόμενα τοῖς συμβεβηκόσιν οἷς ὑπάρχει τὰ ἴδια, and to κίνησις καὶ μέγεθος is added @ συμβέβηκε τοῖς αἰσθητοῖς.