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The common sense is that which judges the things given to it by the other senses.

* The common sense is moved by means of the things given to it by the 5 senses. And these senses are moved by means of the objects, and these objects, sending their likenesses to the 5 senses, from these are transferred to the imprensiva [receptive faculty] and from that to the common sense; and there being judged, they are sent to the memory, in which, according to their power, they are more or less retained.

* The 5 senses are these: seeing, hearing, touching, tasting, smelling.

The ancient speculators concluded that that part of the judgement which is given to man is caused by an instrument, to which the other 5 refer by means of the imprensiva; and to that instrument they gave the name common sense, and they say this sense is in the middle. And they call it by this name of common sense only because it is the common judge of the other 5 senses, that is: seeing, hearing, touching, tasting and smelling. The common sense is moved by means of the imprensiva, which is set in the middle between it and the senses. The imprensiva is moved by means of the likenesses of things given to it by the superficial instruments, that is the senses, which are set in the middle between the external things and the imprensiva; and likewise the senses are moved by means of the objects. The likenesses of the surrounding things send their likenesses to the senses, and the senses transfer them to the imprensiva, the imprensiva sends them to the common sense, and by that they are established in the memory, and there they are more or less retained according to the importance or power of the thing given. That sense is quicker in its office which is nearer to the imprensiva, which is the eye, the chief and prince of the others, of which alone we shall treat, leaving the others so as not to stray too far from our subject. Experience says that the eye extends to 10 various natures of objects; that is: light and darkness, the one the cause of the other 9, the other a privation; colour and body, figure and place, remoteness and nearness, motion and rest.

On the nature of seeing.

I say that seeing is performed by all animals by means of light. And if anyone should allege against this the seeing of nocturnal animals, I shall say these are likewise subject to a similar nature, for it is clearly understood that the senses, receiving the likenesses of things, do not send out from themselves any power; rather, by means of the air that is found between the object and the sense, the air incorporates into itself the species of things, and by the contact it has with the sense conveys them to it, if the objects, whether by sound or by smell, send through the spiritual powers to the ear or to the nose. Here light is not necessary nor is it employed. The forms of objects do not enter by likeness into the air if those objects are not luminous; this being so, the eye cannot receive it from that air which does not have it and which touches its surface. If you would speak of many animals which prey by night, I say that when these lack the little light that suffices for the nature of their eyes, they help themselves with the power of hearing and of smell, which are not impeded by darkness, and in which they far surpass man. If you take note of a cat leaping by day among many vessels, you will see them remain safe, and if it does this same thing by night, it will break a good many. The nocturnal birds do not fly unless the moon shines wholly or in part; rather they feed between the setting of the sun and the entire darkness of night.

No body can be comprehended without light and shadow. Light and shadow are caused by light.