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[348] Nor is the intellect [capable of judging the truth]. For if the intellect is the judge of the truth, it must first know itself. A master-builder does not judge what is straight or crooked without first checking the state of his measuring tools (such as a ruler and compass). Analogously, if the intellect is to be capable of discriminating between truth and falsehood, it must already be aware of its own nature — for example, the substance it is made of, the place where it resides, and everything else. [349] But it is completely incapable of knowing such things. Some (like Dicaearchus) say that it is nothing other than a disposition of the body. Others have said that it does indeed exist, but they cannot agree as to where it is — some, such as Aenesidemus (following Heracleitus) locate it outside the body; others, like certain followers of Democritus, make it co-extensive with the whole body; and others locate it in a part of the body, though again they cannot agree which part. [350] The majority distinguish the intellect from the senses, whereas others identify it with the senses, as if it peered out through holes in the sense organs. This position was first taken by Strato the physicist, and by Aenesidemus. So the intellect is not the means of judging the truth.

[351] There are many intellects; and since they are many, disagreements arise; and since they disagree, they need an arbitrator. Now this will either be another intellect, or something different. It could not be an intellect, since it will be a party to the dispute, and it will need to be judged over, and will no longer be judge. And if it is something different from an intellect, this confirms the view that the intellect is not the judge. [352] I could also use the conclusions drawn by the philosophers as an argument; but I do not want to repeat myself.

Furthermore, most philosophers say that in addition to the intellect, we also have the faculty of sense, which lies in front of the intellect. It necessarily follows that since it lies in front of it, it will prevent the intellect from apprehending external objects. [353] It is just like when a body comes between our sight and what is seen, and prevents the sight from apprehending the object. Similarly, if our sense of vision comes between the intellect and the external object of vision, the sense of vision will prevent the intellect from apprehending the object of vision, since it has no rational dimension. In the same way, if hearing intervenes between the intellect and the sound which is heard, it will prevent the intellect from having any knowledge of what is heard — and the same with all the other senses. So since the intellect is locked inside, and kept in the dark by the senses, it cannot apprehend any of the objects outside it. Consequently, it cannot of itself be said to be the judge of the truth.

[354] The only alternative is to say that both are the judge — that is to say, that the intellect apprehends external objects by using the senses as its assistant. But this again is impossible. The senses do not present external objects to the intellect, but each one reports the specific way in which it is affected. For example, when the sense of touch is warmed by fire, it does not pass on to the intellect the external, burning fire itself, but only the warmth from it, which is the specific way in which it is affected.

[355] However, even this is not right. If the intellect takes into itself the way in which the sense is affected, it becomes sense itself. For whatever receives visual impressions is visually stimulated; and to be visually stimulated is to be vision. Similarly, whatever receives auditory impressions is auditorily stimulated; and to be auditorily stimulated is hearing — and the same with the other senses. [356] Consequently, the intellect too, if it takes into itself the impressions of each sense, is sensorily stimulated; and being sensorily stimulated is sense. But if it is sense, it has no rational dimension. And if it has no rational dimension, it loses its essential being as intellect. And since it is no longer intellect, it cannot take into itself the impressions of sense as intellect.

[357] And even if it receives sense impressions, it will not know external objects. External objects are unlike the ways in which we are affected, and images are utterly different from what they are images of. Take, for example, the image of fire, and the fire itself: the latter burns, whereas the former is not the sort of thing that can burn. Besides, even if we were to suppose that external objects are like the ways in which we are affected, it is absolutely not the case that the intellect apprehends external objects by taking into itself the ways in which we are affected. For if one thing is similar to another, it is different from the thing it is similar to. [358] Consequently, if the intellect knows things which are similar to external objects, it does not know the external objects, but only the things which are similar to them. If someone does not know Socrates, but sees a picture of Socrates, he does not know if Socrates is similar to the picture he experiences. In the same way, when the intellect attends to sense impressions, since it has not observed the external objects themselves, it will not know what they are like, or whether they resemble the impressions.

But if the intellect does not know the contents of experience, it cannot be conscious of the imperceptible things which some people think are known by extrapolation from them. In short, the intellect is in no way the judge of the truth.

[359] But some dogmatists trot out the same reply to the present question as they did to the previous one. They say that these two different parts of the soul (the rational and the non-rational) are not separate. For example, honey is simultaneously both liquid and sweet in every part. In the same way, the soul has two complementary faculties (the rational and the non-rational) which co-operate in its every function. [360] The rational faculty is stimulated by objects of thought, and the non-rational faculty is receptive to objects of experience. Consequently, there is no basis for denying that the intellect (or the soul as a whole) can apprehend the other type of component in the objects of experience. For since it includes both types in its own make-up, it can apprehend both of them directly.

[361] But this is terribly naïve. It may indeed seem that these faculties co-exist in one and the same substance, complement each other, and are present throughout the whole soul. Nevertheless, they belong to entirely different categories of being, and it is one thing to be one of them, and quite a different thing to be the other.

This can be gathered from facts which seem rather obvious. [362] Things can often be considered as belonging to the same substance, but without having the same nature. For example, weight and colour both belong to the same physical object, but they are different from each other. Again, shape and size coincide in one and the same substance, but they have distinct natures, since the intellect conceives size differently from shape. Similarly, the rational faculty in question will still differ from the non-rational faculty, even if they are blended together in the same subject. [363] Putting all the above considerations together, we get the conclusion that the one cannot be stimulated and affected in the same way as the other, since if they were, they would both become a single thing — the intellect would become non-rational if it were affected non-rationally, and the non-rational would become rational if it were stimulated rationally.

[364] Let us now consider the theory that the intellect peers out through the sensory passages as if they were windows, and comes into direct contact with external objects without sense perceptions getting in the way. We shall find that this version leads down a blind alley no less than the previous one. For if the intellect apprehends objects in this way, it must apprehend them as they are in themselves. But as I shall show, nothing is known as it is in itself. Consequently, it is impossible to get at what is true in objects. [n.29] Our opponents say that something is known as it is in itself, if it is known directly, and without the need of anything else to represent it. [365] But nothing is of such a nature as to be known as it is in itself. Everything is known through a passive impression, which is distinct from the active cause of our having an image. [n.30] I have a feeling of sweetness if I am dosed with honey, and I guess that that honey as an external object is sweet. I am warmed if a fire is brought close to me, and I interpret my bodily state as meaning that the fire as an external object is warm. And the same goes for the other senses. [366] Now, everyone agrees that what is known through something else is imperceptible in itself. But everything is perceived through our sense impressions, and our sense impressions are distinct from objects of perception. Consequently, everything external is imperceptible, and therefore unknown to us. For if we were to have any knowledge of something not given in experience, the object would have to include an element which is knowable as it is in itself. But since there is no such element, there can be no knowledge of imperceptible objects.

[367] Someone might accept this argument as showing that external objects are imperceptible, but might still wish to claim that we can know them, on the grounds that our sense impressions are reliable signs of them. However, this too is impossible. If honey comes into contact with my sense of taste, and I am suffused with a feeling of sweetness, it doesn’t mean that the honey itself is sweet (and similarly with the bitterness of wormwood). There is no necessity at all that the passive states which occur in us should also have to occur in the things which actively cause them. A whip striking the flesh causes pain, without there being any pain in the whip; [n.31] and food or drink bring about pleasure in someone who eats or drinks, without there being any pleasure in the food or drink. Similarly, fire can warm, without necessarily being warm itself; and honey can give rise to a sensation of sweetness, without happening to be sweet itself. And the same argument applies to the objects of the other senses. So if, for us to know the truth, something has to be known as it is in itself; and if it has been proved that everything is imperceptible, then it must be accepted that the truth is unknowable.

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