'opinion' is that it is larger than our earth. Imagination at the same time is not possible without sensation: and it follows therefore by this method of elimination that it is that after-effect of sense-perception as which we have already described it. As such it will of course vary in the degree of truth or falsehood it implies with the character of the sensation to which it is attached. If the sensation of which it is the continuance be that of the special qualities of sense, the corresponding picture of imagination will be practically true: should it on the other hand be the "decaying' relique of our common or our incidental senseperceptions, it will of course be several degrees from truth.

The phenomena of dreams, hallucination and illusion form a direct corollary to Aristotle's doctrine of Imagination. Illusion in general is the result of the fact that the faculty of forming pictures of imagination and that of framing judgments are different and employ different standards'. So it is that people form wrong impressions under the influence of passion: or that people in a fever suppose they see animals depicted on the wall. Often of course, Aristotle points out, in the case of such delusions one sense comes in to rectify another. An object held between the crossed fingers appears double to the touch: yet, Aristotle continues, we do not assert the object is twofold, because the sight is more authoritative than the touch. But there is a more characteristic form in which deception may originatea form closely connected with the explanation Aristotle gives of imagination. "The reason" says he "of deception is that pictures of imagination present themselves not only when the object of sensation is itself in movement: it presents itself also if the sense itself be put in movement, supposing it be moved in the same manner as it would have been moved by the object of sense itself." So it is, Aristotle explains, that the earth appears

1 De Insomn. 2, 46ο 16, αἴτιον δὲ τοῦ συμβαίνειν ταῦτα τὸ μὴ κατὰ τὴν αὐτὴν δύναμιν κρίνειν τό τε κύριον καὶ ᾧ τὰ φαντάσματα γίνεται.

2 460b20.

3 De Insomn. 2, 460 23-26, τοῦ δὲ διεψεῦσθαι αἴτιον ὅτι οὐ μόνον τοῦ αἰσθητοῦ

to people when they sail to be in movement, because the organ of vision is moved in the same way as it would be if the earth were really in movement. Illusion then in this case is the result of the fact that a bodily excitation suggests and originates a picture of the very object which might actually have caused this sensuous affection.

This theory of Illusion serves also with Aristotle as an explanation of dreaming. Just as the movement of the eye in the person sailing gives rise to the idea that the earth itself is moved : so similarly a dream is the result of a movement excited whether from without or from within, in our bodily organs. The conditions which create dreaming may thus be said to be present just as much by day as during night. But there is a particula circumstance which comes in to explain the greater efficacy of these conditions during sleep'. And this circumstance depends so far upon the nature of sleep itself that it may be advisable to add here a word on Aristotle's theory upon this subject.

Sleep and waking are, according to Aristotle, two phenomena which characterize animals as opposed to plants, and they belong simply to those creatures which possess a faculty of sense-perception. Both sleep and waking are thus affections of our sensitive capacities but as contraries they stand towards those functions in two entirely opposite relations. Waking, in short, is identical with the free play of our faculties of sense (τῷ λελύσθαι τὴν aloenow), sleep is, on the contrary, the result of restriction and quiescence on the part of these same faculties. But this freedom or imprisonment of sense is not a matter which affects one or other of the senses separately; it affects them altogether. Sleep,

κινουμένου φαίνεται ἁδήποτε, ἀλλὰ καὶ τῆς αἰσθήσεως κινουμένης αὐτῆς, ἐὰν ὡσαύτως κινῆται ὥσπερ καὶ ὑπὸ τοῦ αἰσθητοῦ.

1 De Insomn. 3, 4602S, οὐ μόνον ἐγρηγορότων αἱ κινήσεις αἱ ἀπὸ τῶν αἰσθημάτων γινόμεναι...ἀλλὰ καὶ ὅταν γένηται...ὕπνος, καὶ μᾶλλον τότε φαίνονται. μεθ' ἡμέραν μὲν γὰρ ἐκκρούονται.

2 De Somn. 1, 454528, ἄνευ μὲν γὰρ αἰσθήσεως οὐχ ὑπάρχει οὔθ ̓ ὕπνος οὔτ ̓ ἐγρήγορσις.

3

4:41ο, ὁ γὰρ ὕπνος τι τοῦ αἰσθητικοῦ μορίου ἐστίν, οἷον δεσμὸς καὶ ἀκινησία τις.

that is to say, is, no less than waking, a phenomenon of that central sense which we have seen serves as foundation for the work of perception. But the organ within which the operations of this central sense is carried on is, we have seen before, the heart and sleep thus comes to be an effect of the action of the heart. Sleep, in fact, is not any incapacity whatever on the part of our perceptive faculty: it must be distinguished from such unnatural phases of this incapacity as insanity, choking or fainting. In most cases it is a result of the process of digestion-the food, that is to say, which has been taken into the body rises in the process of digestion to the head, causes there a heaviness, and descending, expels the heat: it may also result from labour or disease, but simply in both cases because the upper parts of the body have been made cool in the manner we have described. And therefore Aristotle's most explicit account of the phenomenon of sleep refers it to the circuit in reverse order and in considerable volume (ἀντιπερίστασις ἀθρόως) made by the substantial nutriment which has been carried by the natural heat

thin the body on to the primary organ of sensation'.

The movements therefore which result in dreams are present just as much by day as during night: but by day they are expelled through the simultaneous action of the senses and the understanding. "But at night, by reason of the inactivity of the particular senses, these movements are carried downward to the origin and principle of our perceptive faculties, and so become clear and conspicuous, after the commotion of this current has been composed." Thus then the blood in its descent toward the heart carries with it movements whether they be potential or

1 De Somn. 458525, τί μὲν οὖν τὸ αἴτιον τοῦ καθεύδειν εἴρηται, ὅτι ἡ ὑπὸ τοῦ σωματώδους τοῦ ἀναφερομένου ὑπὸ τοῦ συμφύτου θερμοῦ ἀντιπερίστασις ἀθρόως ἐπὶ τὸ πρῶτον αἰσθητήριον· καὶ τί ἐστιν ὁ ὕπνος ὅτι τοῦ πρώτου αἰσθητηρίου κατάληψις πρὸς τὸ μὴ δύνασθαι ἐνεργεῖν.

* Di Insomn. 461*+, νύκτωρ δὲ δι' ἀργίαν τῶν κατὰ μόριον αἰσθήσεων καὶ ἀδυναμίαν τοῦ ἐνεργεῖν, διὰ τὸ ἐκ τῶν ἔξω εἰς τὸ ἐντὸς γίνεσθαι τὴν τοῦ θερμοῦ παλίρ ροιαν, ἐπὶ τὴν ἀρχὴν τῆς αἰσθήσεως καταφέρονται καὶ γίνονται φανεραὶ καθισταμένης τῆς ταραχής.

actual. Of these movements now one, now another, comes to the surface: they emerge and operate when freed from the stronger motion which keeps them in check: just as (Aristotle adds the illustration) artificial frogs rise to the surface of the water when the salt with which they are surrounded melts away. Released, then, from the other movements which obstruct them, they protract their movement outwards to the little blood which still remains within the organs of sense, and thus give rise to impressions and create pictures of imagination much in the same way as the rapid changes in the clouds cause them to be viewed as men and centaurs. Dreams, then, Aristotle concludes, are movements which give rise to images within our organs of perception (κινήσεις φανταστικαὶ ἐν τοῖς αἰσθητηρίοις). There are of course cases in which dreams are the result of semi-conscious sensations, half-heard sounds or half seen lights: and reflections and ideas are often added to them. But in itself dreaming is simply the result of the movement of our sensations during the period of sleep as such1.

The materialistic character of Aristotle's conception of pavTaoía need now be scarcely noted. The pictures which imagination, either in our waking moments or in our dreams, presents to us are simply the result of a physiological process, in which the movement of the organ of sensation continues the impression which either originally excited it, or might at least have originally done so. The pictures or images themselves are conceived in genuine materialistic fashion-as seal impressions, through which it becomes possible to see that which is itself absent, but is present in its representative effect: they are traces, or moulds, left behind in our organism, and thus, where there is too much movement, or where the brain is either too hard or too soft, the impressions we are now discussing do not manage to subsist.

The materialist aspects of the process do not however exhaust Aristotle's account of our image-forming faculty. We must re

1 De Insomn. 462329, τὸ φάντασμα τὸ ἀπὸ τῆς κινήσεως τῶν αἰσθημάτων, ὅταν ἐν τῷ καθεύδειν ᾖ, ᾗ καθεύδει, τοῦτ' ἐστὶν ἐνύπνιον.

member, as we have had occasion to remark before, the background given to the whole Aristotelian Psychology by the ʊyń as the truth or reality of body. Particularly we must take into account the fact that sense-perception is no mere material assimilation of the outward world but in its last resort depends upon that central faculty of sense, through which we have the power of comparing and combining our sensations. Thus the pictures of imagination, though dependent on the sensations. which have passed away, are not of a merely sensuous character: they become through that own divaμis of sense generalized conceptions of an object—they are αἰσθήματα but ἄνευ ὕλης: and the images of our imaginative faculty often approximate closely to the ideas of thought'. It is within its semi-sensuous images that reason comes to grasp its ethical ideas; and its images, though immediately limited to the domain of sense, may become the basis of deliberation and thought. Thought indeed, as well as sense, Aristotle himself says, may originate imagination; and in another passage the imaginative faculty is looked at as a species of thought3.

The representative images of phantasy are to Aristotle the stepping-stone to memory and recollection. It seems in fact at first sight difficult to draw any decided line between these reliques of sensation which form the pictures of imagination and those survivals of the past which constitute a memory; and Aristotle himself does not always distinguish them. At the same time there is a real difference between them. The phantasm carries with it little connotation of truth or falsehood in the form of a reference to some external object, and it implies no relation to any time in past experience at which it was originally presented. Memory however carries with it both these attributes-it implies at once an object to which it corresponds, and

1 De An. III. 8, 4329, τὰ γὰρ φαντάσματα ὥσπερ αἰσθήματά ἐστι πλὴν ἄνευ ὕλης.

2 Ibid. III. 7, 4311, τὰ μὲν οὖν εἴδη τὸ νοητικὸν ἐν τοῖς φαντάσμασι νοεῖ.

3 Ibid. 111. 10, 43310, εἴ τις τὴν φαντασίαν τιθείη ὡς νόησίν τινα.