Imagination is a faculty of the unreasoning part of the soul. It is through the organs of sense that it is brought into action, and it is spoken of as sensation. And further, what is imagined and perceived is that which comes within the scope of the faculty of imagination and sensation. For example, the sense of sight is the visual faculty itself, but the object of sight is that which comes within the scope of the sense of sight, such as a stone or any other such object. Further, an imagination is an affection of the unreasoning part of the soul which is occasioned by some object acting upon the sensation. But an appearance is an empty affection of the unreasoning part of the soul, not occasioned by any object acting upon the sensation. Moreover the organ of imagination is the anterior ventricle of the brain.
Sensation is that faculty of the soul whereby material objects can be apprehended or discriminated. And the sensoria are the organs or members through which sensations are conveyed. And the objects of sense are the things that come within the province of sensation. And lastly, the subject of sense is the living animal which possesses the faculty of sensation. Now there are five senses, and likewise five organs of sense.
The first sense is sight: and the sensoria or organs of sight are the nerves of the brain and the eyes. Now sight is primarily perception of colour, but along with the colour it discriminates the body that has colour, and its size and form, and locality, and the intervening space and the number : also whether it is in motion or at rest, rough or smooth, even or uneven, sharp or blunt, and finally whether its composition is watery or earthy, that is, wet or dry.
The second sense is hearing, whereby voices and sounds are perceived. And it distinguishes these as sharp or deep, or smooth or loud. Its organs are the soft nerves of the brain, and the structure of the ears. Further, man and the ape are the only animals that do not move their ears.
The third sense is smell, which is caused by the nostrils transmitting the vapours to the brain: and it is bounded by the extreme limits of the anterior ventricle of the brain. It is the faculty by which vapours are perceived and apprehended. Now, the most generic distinction between vapours is whether they have a good or an evil odour, or form an intermediate class with neither a good nor an evil odour. A good odour is produced by the thorough digestion in the body of the humours. When they are only moderately digested the intermediate class is formed, and when the digestion is very imperfect or utterly wanting, an evil odour results.
The fourth sense is taste: it is the faculty whereby the humours are apprehended or perceived, and its organs of sense are the tongue, and more especially the lips, and the palate (which the Greeks call ouraniskou), and in these are nerves that come from the brain and are spread out, and convey to the dominant part of the soul the perception or sensation they have encountered. The so-called gustatory qualities of the humours are these:--sweetness, pungency, bitterness, astringency, acerbity, sourness, saltness, fattiness, stickiness; for taste is capable of discriminating all these. But water has none of these qualities, and is therefore devoid of taste. Moreover, astringency is only a more intense and exaggerated form of acerbity.
The fifth sense is touch, which is common to all living things. Its organs are nerves which come from the brain and ramify all through the body. Hence the body as a whole, including even the other organs of sense, possesses the sense of touch. Within its scope come heat and cold, softness and hardness, viscosity and brittleness, heaviness and lightness: for it is by touch alone that these qualities are discriminated. On the other hand, roughness and smoothness, dryness and wetness, thickness and thinness, up and down, place and size, whenever that is such as to be embraced in a single application of the sense of touch, are all common to touch and sight, as well as denseness and rareness, that is porosity, and rotundity if it is small, and some other shapes. In like manner also by the aid of memory and thought perception of the nearness of a body is possible, and similarly perception of number up to two or three, and such small and easily reckoned figures. But it is by sight rather than touch that these things are perceived.
The Creator, it is to be noted, fashioned all the other organs of sense in pairs, so that if one were destroyed, the other might fill its place. For there are two eyes, two ears, two orifices of the nose, and two tongues, which in some animals, such as snakes, are separate, but in others, like man, are united. But touch is spread over the whole body with the exception of bones, nerves, nails, horns, hairs, ligaments, and other such structures.
Further, it is to be observed that sight is possible only in straight lines, whereas smell and hearing are not limited to straight lines only, but act in all directions. Touch, again, and taste act neither in straight lines, nor in every direction, but only when each comes near to the sensible objects that are proper to it.
The faculty of thought deals with judgments and assents, and impulse to action and disinclinations, and escapes from action: and more especially with thoughts connected with what is thinkable, and the virtues and the different branches of learning, and the theories of the arts and matters of counsel and choice. Further, it is this faculty which prophesies the future to us in dreams, and this is what the Pythagoreans, adopting the Hebrew view, hold to be the one true form of prophecy. The organ of thought then is the mid-ventricle of the brain, and the vital spirit it contains.
The faculty of memory is the cause and storehouse of remembrance and recollection. For memory is a fantasy s that is left behind of some sensation and thought manifesting itself in action; or the preservation of a sensation and thought. For the soul comprehends objects of sense through the organs of sense, that is to say, it perceives, and thence arises a notion: and similarly it comprehends the objects of thought through the mind, and thence arises a thought. It is then the preservation of the types of these notions and thoughts that is spoken of as memory.
Further, it is worthy of remark that the apprehension of matters of thought depends on learning, or natural process of thought, and not on sensation. For though objects of sense are retained in the memory by themselves, only such objects of thought are remembered as we have learned, and we have no memory of their essence.
Recollection is the name given to the recovery of some memory lost by forgetfulness. For forgetfulness is just loss of memory. The faculty of imagination then, having apprehended material objects through the senses, transmits this to the faculty of thought or reason (for they are both the same), and this after it has received and passed judgment on it, passes it on to the faculty of memory. Now the organ of memory is the posterior ventricle of the brain, which the Greeks call the paregkefalis, and the vital spirit it contains.
Again the reasoning part of the soul is divided into conception and articulation. Conception is an activity of the soul originating in the reason without resulting in utterance. Accordingly, often, even when we are silent we run through a whole speech in our minds, and hold discussions in our dreams. And it is this faculty chiefly which constitutes us all reasoning beings. For those who are dumb by birth or have lost their voice through some disease or injury, are just as much reasoning beings. But articulation by voice or in the different dialects requires energy: that is to say, the word is articulated by the tongue and mouth, and this is why it is named articulation. It is, indeed, the messenger of thought, and it is because of it that we are called speaking beings.