What is Perception?

17. The Functions of the Soul

The soul has 2 functions:

1. Actions

These are all our wills. Our will comes directly from our soul and seem to depend only on it.

2. Passions

These are all the kinds of perceptions or knowledge that are found in us. Often, it is not our soul that makes them as they are, and it always receives them from the things that are represented by them.

18. The Will

Our wills are of 2 kinds:

1. Some are actions of the soul that end in the soul itself, such as when we want to love God or generally apply our thought to some object that is not material.
2. Others are actions that end in our body, such as when, from the mere fact that we have the will to walk, it follows that our legs move and we walk.

19. Perception

Our perceptions are also of 2 kinds:

1. Those that are caused by the soul

These are the perceptions of our wills, and of all imaginations or other thoughts that depend on them. This is because we cannot will anything without perceiving at the same time that we will it.

This will comes from our passions.

2. Those that are caused by the body

20. The Imaginations and Other Thoughts Formed by the Soul

When our soul applies itself to imagine something that is not, such as to represent an enchanted palace or a chimera; and also when it applies itself to consider something that is only intelligible and not imaginable, for example, to consider its own nature, the perceptions it has of these things depend mainly on the will that makes it perceive them.

Therefore, they are usually considered actions rather than passions.

21. The Imaginations That Have Only the Body for Their Cause

Among the perceptions caused by the body, most depend on the nerves.

But there are also some that do not depend on them. These are called imaginations, like those I have just spoken of, which nevertheless differ in that our will does not apply itself to form them; which means that they cannot be counted among the actions of the soul.

They only arise from the fact that the spirits, being variously agitated and encountering the traces of various impressions that have preceded in the brain, take their course fortuitously through certain pores rather than others.

Such are the illusions of our dreams, and also the daydreams we often have when awake, when our thought wanders listlessly, without applying itself to anything in particular.

Although some of these imaginations are passions of the soul, taking this word in its most proper and particular meaning; and although they can all be thus named if we take it in a more general meaning: nevertheless, because they do not have such a notable and determined cause as the perceptions the soul receives through the nerves, and because they seem to be only the shadow and painting of them, before we can distinguish them well, we must consider the difference that exists between these others.

22. The Difference Between Various Perceptions

There are perceptions that I have not yet explained come to the soul through the nerves, and there is this difference between them: some we attribute to external objects that strike our senses, others to our body or to some of its parts, and finally others to our soul.

23. Perceptions We Attribute to External Objects

Those that we attribute to things outside of us, namely to the objects of our senses, are caused (at least when our opinion is not false) by these objects, which, exciting some movements in the organs of the external senses, also excite movements in the brain through the nerves, which make the soul feel them.

Thus, when we see the light of a torch and hear the sound of a bell, this sound and this light are two different actions, which, by merely exciting two different movements in some of our nerves, and through them in the brain, give the soul two different feelings, which we relate so much to the subjects we suppose to be their causes, that we think we see the torch itself and hear the bell, not just feel the movements that come from them.

24. Perceptions We Attribute to Our Body

The perceptions we attribute to our body or some of its parts are those we have of hunger, thirst, and our other natural appetites; to which can be added pain, heat, and other affections we feel as in our members, and not as in objects outside of us.

Thus, we can feel at the same time, and through the same nerves, the coldness of our hand and the heat of the flame it approaches; or conversely the heat of the hand and the cold of the air it is exposed to.

There is no difference between the actions that make us feel the heat or cold that is in our hand and those that make us feel the one that is outside of us, except that one of these actions occurring with the other, we judge that the first is already in us and that the one that follows is not yet in us but in the object causing it.

25. Perceptions We Attribute to Our Soul

The perceptions that are attributed only to the soul are those whose effects are felt as within the soul itself, and for which no proximate cause is commonly known to which they can be attributed.

Such are feelings of joy, anger, and similar emotions, which are sometimes excited in us by objects that move our nerves and sometimes also by other causes.

Now, although all our perceptions, both those attributed to objects outside of us and those attributed to various affections of our body, are truly passions with regard to our soul, when taking this word in its most general meaning, it is customary to restrict it to signify only those that relate to the soul itself. And it is only these last ones that I have undertaken to explain here under the name of the passions of the soul.

26. Imaginations That Depend Only on the Fortuitous Movement of Spirits Can Be as True Passions as Perceptions That Depend on Nerves

All the same things that the soul perceives through the nerves can also be represented to it by the fortuitous course of the spirits.

The only difference is that the impressions that enter the brain through the nerves are usually more vivid and more distinct than those that the spirits excite there.

This made me say in Article 21 that the latter are like the shadow or the painting of the former.

Sometimes, this painting is so similar to the thing it represents that one can be deceived about the perceptions that relate to objects outside of us or those that relate to some parts of our body, but one cannot be deceived in the same way about the passions, because they are so close and so internal to our soul that it is impossible for it to feel them without them truly being as it feels them.

Thus, often when one is asleep, and even sometimes when awake, one imagines certain things so strongly that one thinks one sees them before oneself or feels them in one’s body, although they are not there at all.

But although one is asleep and dreaming, one cannot feel sad or moved by some other passion without it being very true that the soul has this passion within itself.