ARTICLE XVI.
How all the members may be moved by the objects of the senses and by the animal spirits without the aid of the soul.
We must finally remark that the machine of our body is so formed that all the changes undergone by the movement of the spirits may cause them to open certain pores in the brain more than others, and reciprocally that when some one of the pores is opened more or less than usual (to however small a degree it may be) by the action of the nerves which are employed by the senses, that changes something in the movement of the spirits and causes them to be conducted into the muscles which serve to move the body in the way in which it is usually moved when such an action takes place. In this way all the movements which we make without our will contributing thereto (as frequently happens when we breathe, walk, eat, and in fact perform all those actions which are common to us and to the brutes), only depend on the conformation of our members, and on the course which the spirits, excited by the heat of the heart, follow naturally in the brain, nerves, and muscles, just as the movements of a watch are produced simply by the strength of the springs and the form of the wheels.
ARTICLE XVII.
What the functions of the soul are.
After having thus considered all the functions which pertain to the body alone, it is easy to recognise that there is nothing in us which we ought to attribute to our soul excepting our thoughts, which are mainly of two sorts, the one being the actions of the soul, and the other its passions. Those which I call its actions are all our desires, because we find by experience that they proceed directly from our soul, and appear to depend on it alone: while, on the other hand, we may usually term one’s passions all those kinds of perception or forms of knowledge which are found in us, because it is often not our soul which makes them what they are, and because it always receives them from the things which are represented by them.
ARTICLE XVIII.
Of the Will.
Our desires, again, are of two sorts, of which the one consists of the actions of the soul which terminate in the soul itself, as when we desire to love God, or generally speaking, apply our thoughts to some object which is not material; and the other of the actions which terminate in our body, as when from the simple fact that we have the desire to take a walk, it follows that our legs move and that we walk.
ARTICLE XIX.
Of the Perceptions.
Our perceptions are also of two sorts, and the one have the soul as a cause and the other the body. Those which have the soul as a cause are the perceptions of our desires, and of all the imaginations or other thoughts which depend on them. For it is certain that we cannot desire anything without perceiving by the same means that we desire it; and, although in regard to our soul it is an action to desire something, we may say that it is also one of its passions to perceive that it desires. Yet because this perception and this will are really one and the same thing, the more noble always supplies the denomination, and thus we are not in the habit of calling it a passion, but only an action.
ARTICLE XX.
Of the imaginations and other thoughts which are formed by the soul.
When our soul applies itself to imagine something which does not exist, as when it represents to itself an enchanted palace or a chimera, and also when it applies itself to consider something which is only intelligible and not imaginable, e g to consider its own nature, the perceptions which it has of these things depend principally on the act of will which causes it to perceive them. That is why we usually consider them as actions rather than passions.
ARTICLE XXI.
Of the imaginations which have the body only as a cause.
Amongst the perceptions which are caused by the body, the most part depend on the nerves; but there are also some which do not depend on them, and which we name imaginations, such as those of which I have just spoken, from which they yet differ inasmuch as our will has no part in forming them; and this brings it to pass that they cannot be placed in the number of the actions of the soul. And they only proceed from the fact that the spirits being agitated in diverse ways and meeting with traces of diverse preceding impressions which have been effected in the brain, take their course there fortuitously by certain pores rather than by others. Such are the illusions of our dreams, and also the day-dreams which we often have when awake, and when our thought wanders aimlessly without applying itself to anything of its own accord. But, although some of these imaginations are the passions of the soul, taking this word in its most correct and perfect significance, and since they may all be thus termed if we take it in a more general significance, yet, because they have not a cause of so notable and determinate a description as the perceptions which the soul receives by the intermission of the nerves, and because they appear to be only a shadow and a picture, we must, before we can distinguish them very well, consider the difference prevailing among these others.
ARTICLE XXII.
Of the difference which exists among the other perceptions.
All the perceptions which I have not yet explained come to the soul by the intermission of the nerves, and there is between them this difference, that we relate them in the one case to objects outside which strike our senses, in the other to our soul.
ARTICLE XXIII.
Of the perceptions which we relate to objects which are without us.
Those which we relate to the things which are without us, to wit to the objects of our senses, are caused, at least when our opinion is not false, by these objects which, exciting certain movements in the organs of the external senses, excite them also in the brain by the intermission of the nerves, which cause the soul to perceive 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, simply by the fact that they excite two different movements in certain of our nerves, and by these means in the brain, give two different sensations to the soul, which sensations we relate to the subjects which we suppose to be their causes in such a way that we think we see the torch itself and hear the bell, and do not perceive just the movements which proceed from them.
ARTICLE XXIV.
Of the perceptions which we relate to our body.
The perceptions which we relate to our body, or to some of its parts, are those which we have of hunger, thirst, and other natural appetites, to which we may unite pain, heat, and the other affections which we perceive as though they were in our members, and not as in objects which are outside us; we may thus perceive at the same time and by the intermission of the same nerves, the cold of our hand and the heat of the flame to which it approaches; or, on the other hand, the heat of the hand and the cold of the air to which it is exposed, without there being any difference between the actions which cause us to feel the heat or the cold which is in our hand, and those which make us perceive that which is without us, excepting that from the one of these actions following upon the other, we judge that the first is already in us, and what supervenes is not so yet, but is in the object which causes it.
ARTICLE XXV.
Of the perceptions which we relate to our soul.
The perceptions which we relate solely to the soul are those whose effects we feel as though they were in the soul itself, and as to which we do not usually know any proximate cause to which we may relate them: such are the feelings of joy, anger, and other such sensations, which are sometimes excited in us by the objects which move our nerves and sometimes also by other causes. But, although all our perceptions, both those which we relate to objects which are outside us, and those which we relate to the diverse affections of our body, are truly passions in respect of our soul, when we use this word in its most general significance, yet we are in the habit of restricting it to the signification of those alone which are related to soul itself; and it is only these last which I have here undertaken to explain under the name of the passions of the soul.
ARTICLE XXVI.
That the imaginations which only depend on the fortuitous movements of t
he spirits, may be passions just as truly as the perceptions which depend on the nerves.
It remains for us to notice here that all the same things which the soul perceives by the intermission of the nerves, may also be represented by the fortuitous course of the animal spirits, without there being any other difference excepting that the impressions which come into the brain by the nerves are usually more lively or definite than those excited there by the spirits, which caused me to say in Article XXI that the former resemble the shadow or picture of the latter. We must also notice that it sometimes happens that this picture is so similar to the thing which it represents that we may be mistaken therein regarding the perceptions which relate to objects which are outside us, or at least those which relate to certain parts of our body, but that we cannot be so deceived regarding the passions, inasmuch as they are so close to, and so entirely within our soul, that it is impossible for it to feel them without their being actually such as it feels them to be. Thus often when we sleep, and sometimes even when we are awake, we imagine certain things so forcibly, that we think we see them before us, or feel them in our body, although they do not exist at all; but although we may be asleep, or dream, we cannot feel sad or moved by any other passion without its being very true that the soul actually has this passion within it.
ARTICLE XXVII.
The definition of the passions of the soul.
After having considered in what the passions of the soul differ from all its other thoughts, it seems to me that we may define them generally as the perceptions, feelings, or emotions of the soul which we relate specially to it, and which are caused, maintained, and fortified by some movement of the spirits.
ARTICLE XXVIII.
Explanation of the first part of this definition.
We may call them perceptions when we make use of this word generally to signify all the thoughts which are not actions of the soul, or desires, but not when the term is used only to signify clear cognition; for experience shows us that those who are the most agitated by their passions, are not those who know them best; and that they are of the number of perceptions which the close alliance which exists between the soul and the body, renders confused and obscure. We may also call them feelings because they are received into the soul in the same way as are the objects of our outside senses, and are not otherwise known by it; but we can yet more accurately call them emotions of the soul, not only because the name may be attributed to all the changes which occur in it — that is, in all the diverse thoughts which come to it, but more especially because of all the kinds of thought which it may have, there are no others which so powerfully agitate and disturb it as do these passions.
ARTICLE XXIX.
Explanation of the second part.
I add that they particularly relate to the soul, in order to distinguish them from the other feelings which are related, the one to outside objects such as scents, sounds, and colours; the others to our body such as hunger, thirst, and pain. I also add that they are caused, maintained, and fortified by some movement of the spirits, in order to distinguish them from our desires, which we may call emotions of the soul which relate to it, but which are caused by itself; and also in order to explain their ultimate and most proximate cause, which plainly distinguishes them from the other feelings.
ARTICLE XXX.
That the soul is united to all the portions of the body conjointly.
But in order to understand all these things more perfectly, we must know that the soul is really joined to the whole body, and that we cannot, properly speaking, say that it exists in any one of its parts to the exclusion of the others, because it is one and in some manner indivisible, owing to the disposition of its organs, which are so related to one another that when any one of them is removed, that renders the whole body defective; and because it is of a nature which has no relation to extension, nor dimensions, nor other properties of the matter of which the body is composed, but only to the whole conglomerate of its organs, as appears from the fact that we could not in any way conceive of the half or the third of a soul, nor of the space it occupies, and because it does not become smaller owing to the cutting off of some portion of the body, but separates itself from it entirely when the union of its assembled organs is dissolved.
ARTICLE XXXI.
That there is a small gland in the brain in which the soul exercises its functions more particularly than in the other parts.
It is likewise necessary to know that although the soul is joined to the whole body, there is yet in that a certain part in which it exercises its functions more particularly than in all the others; and it is usually believed that this part is the brain, or possibly the heart: the brain, because it is with it that the organs of sense are connected, and the heart because it is apparently in it that we experience the passions. But, in examining the matter with care, it seems as though I had clearly ascertained that the part of the body in which the soul exercises its functions immediately is in nowise the heart, nor the whole of the brain, but merely the most inward of all its parts, to wit, a certain very small gland which is situated in the middle of its substance and so suspended above the duct whereby the animal spirits in its anterior cavities have communication with those in the posterior, that the slightest movements which take place in it may alter very greatly the course of these spirits; and reciprocally that the smallest changes which occur in the course of the spirits may do much to change the movements of this gland.
ARTICLE XXXII.
How we know that this gland is the main seat of the soul.
The reason which persuades me that the soul cannot have any other seat in all the body than this gland wherein to exercise its functions immediately, is that I reflect that the other parts of our brain are all of them double, just as we have two eyes, two hands, two ears, and finally all the organs of our outside senses are double; and inasmuch as we have but one solitary and simple thought of one particular thing at one and the same moment, it must necessarily be the case that there must somewhere be a place where the two images which come to us by the two eyes, where the two other impressions which proceed from a single object by means of the double organs of the other senses, can unite before arriving at the soul, in order that they may not represent to it two objects instead of one. And it is easy to apprehend how these images or other impressions might unite in this gland by the intermission of the spirits which fill the cavities of the brain; but there is no other place in the body where they can be thus united unless they are so in this gland.
ARTICLE XXXIII.
That the seat of the passions is not in the heart.
As to the opinion of those who think that the soul receives its passions in the heart, it is not of much consideration, for it is only founded on the fact that the passions cause us to feel some change taking place there; and it is easy to see that this change is not felt in the heart excepting through the medium of a small nerve which descends from the brain towards it, just as pain is felt as in the foot by means of the nerves of the foot, and the stars are perceived as in the heavens by means of their light and of the optic nerves: so that it is not more necessary that our soul should exercise its functions immediately in the heart, in order to feel its passions there, than it is necessary for the soul to be in the heavens in order to see the stars there.
ARTICLE XXXIV.
How the soul and the body act on one another.
Let us then conceive here that the soul has its principal seat in the little gland which exists in the middle of the brain, from whence it radiates forth through all the remainder of the body by means of the animal spirits, nerves, and even the blood, which, participating in the impressions of the spirits, can carry them by the arteries into all the members. And recollecting what has been said above about the machine of our body, i.e. that the little filaments of our nerves are so distributed in all its parts, that on the occasion of the diverse movements which are there excited by sensible objects, they open in diverse ways the pores of the brain,
which causes the animal spirits contained in these cavities to enter in diverse ways into the muscles, by which means they can move the members in all the different ways in which they are capable of being moved; and also that all the other causes which are capable of moving the spirits in diverse ways suffice to conduct them into diverse muscles; let us here add that the small gland which is the main seat of the soul is so suspended between the cavities which contain the spirits that it can be moved by them in as many different ways as there are sensible diversities in the object, but that it may also be moved in diverse ways by the soul, whose nature is such that it receives in itself as many diverse impressions, that is to say, that it possesses as many diverse perceptions as there are diverse movements in this gland. Reciprocally, likewise, the machine of the body is so formed that from the simple fact that this gland is diversely moved by the soul, or by such other cause, whatever it is, it thrusts the spirits which surround it towards the pores of the brain, which conduct them by the nerves into the muscles, by which means it causes them to move the limbs.