1. What is a passion with regard to one subject is always an action in some other regard
In the first place, I note that whatever takes place or occurs is generally called by philosophers a
‘passion’ with regard to the subject to which it happens and an ‘action’ with regard to that which
makes it happen. Thus, although an agent and patient are often quite different, an action and
passion must always be a single thing which has theses two names on account of the two
different subjects to which it may be related.
2. To understand the passions of the soul we must distinguish its functions from those of the
body.
Next I note that we are not aware of any subject which acts more directly upon our soul than the
body to which it is joined. Consequently we should recognize that what is a passion in the soul is
usually an action in the body.
3. The rule we must follow in order to do this
Anything that we experience as being in us, and which we see can also exist in wholly inanimate
bodies, must be attributed only to our body. On the other hand, anything in us which we cannot
conceive in any way as capable of belonging to a body must be attributed to our soul.
4. The heat and the movement of the limbs proceed from the body, and thoughts from the soul
Thinking belongs to the soul. All the heat and all the movements belong solely to the body.
5. It is an error to believe that the soul gives movement and heat to the body
It has been believed, without justification, that our natural heat and all the movements of our
bodies depend on the soul; whereas we ought to hold, on the contrary, that the soul takes its
leave when we die only because this heat ceases and the organs which bring about bodily
movement decay.
6. The difference between a living body and a dead body
So as to avoid this error, let us note that death never occurs through the absence of the soul, but
only because one of the principal parts of the body decays.
7. A brief account of the parts of the body and of some of their functions
See page 332
8. The principle underlying all these functions
While we are alive there is a continual heat in our hearts, which is a kind of fire that the blood of
the veins maintains there. This fire is the corporeal principle underlying all the movements of our
limbs.
9. How the movement of the heart takes place
,Its first effect is that it makes the blood which fills the cavities of the heart expand. This causes
the blood, now needing to occupy a larger space, to rush from the right-hand cavity into the
arterial vein and from the left-hand cavity into the great artery. Then, when this expansion
ceases, fresh blood immediately enters the right-hand cavity of the heart from the vena cava,
and the left-hand cavity from the venous artery. This and this alone is what the pulse or beating
of the heart and arteries consists in, and it explains why the beating is repeated each time new
blood enters the heart. It is also the sole cause of the movement of the blood, making it flow
constantly and very rapidly in all the arteries and veins, so that it carries the heat it acquires in
the heart to all the other parts of the body, and provides them with nourishment.
10. How the animal spirits are produced in the brain
What is, however, more worthy of consideration here is that all the most lively and finest parts
of the blood, which have been rarefied by the heat in the heart, constantly enter the cavities of
the brain in large numbers. What makes them go there rather than elsewhere is that all the
blood leaving the heart through the great artery follows a direct route towards this place, and
since not all this blood can enter there, only the most active and finest parts pass into it while the
rest spread out into the other regions of the body. Now these very fine parts of the blood make
up the animal spirit.
11. How the movements of the muscles take place
What causes one muscle to become shorter rather than its opposite is simply that fractionally
more spirits from the brain come to it than to the other. This is easy to understand, provided one
knows that very few animal spirits come continually form the brain to each muscle, and that any
muscle always contains a quantity of its own spirits. In each of the muscles there are small
openings through which the spirits may flow from one into the other, and which are so arranged
that when the spirits coming from the brain to one of the muscles are slightly more forceful than
those going to the other. In this way all the spirits previously contained in the two muscles are
gathered very rapidly in one of them, thus making it swell and become shorter, while the other
lengthens and relaxes.
12. How external objects act upon the sense organs
We still have to know what causes the spirits not to flow always in the same way from the brain
to the muscles, but to come sometimes more to some muscles than to others. In our case,
indeed, one of these causes is the activity of the soul. But in addition we must note two other
causes, which depend solely on the body. The first consists in differences in the movements
produced in the sense organs by their objects.
13. This action of external objects may direct the spirits into the muscles in various different ways
I explained in the ‘optics’ how the objects of sight make themselves known to us simply by
producing, through the medium of the intervening transparent bodies, local motions in the optic
nerve-fibres at the back of our eyes, and then in the regions of the brain where these nerves
originate. I explained too that the objects produce as much variety in these motions as they
cause us to see in the things, and that it is not the motions occurring in the eye, but those
occurring in the brain, which directly represent these objects to the soul. By this example, it is
easy to conceive how sounds, smells, tastes, heat, pain, hunger, thirst and, in general, all the
objects both of our external senses and of our internal appetites, also produce some movement
in our nerves, which passes through them into the brain. Besides causing our soul to have various
,different sensations, these various movements in the brain can also act without the soul, causing
the spirits to make their way to certain muscles rather than others, and so causing them to move
our limbs.
14. Differences among the spirits may also cause them to take various different courses
The other cause which serves to direct the animal spirits to the muscles in various different ways
is the unequal agitation of the spirits and differences in their parts.
15. The causes of these differences
And this inequality may arise from the different materials of which the spirits are composed. One
sees this in the case of those who have drunk a lot of wine. Such an inequality of the spirits may
also arise from various conditions of the heart, liver, stomach, spleen and all the other organs
that help produce them.
16. How all the limbs can be moved by the objects of the sense by the spirits without the help of
the soul
Finally it must be observed that the mechanism of our body is so composed that all the changes
occurring in the movement of the spirits may cause them to open some pores in the brain more
than others. Conversely, when one of the pores is opened somewhat more or less than usual by
an action of the sensory nerves, this brings about a change in the movement of the spirits and
directs them to the muscles which serve to move the body in the way it is usually moved on the
occasion of such an action.
17. The functions of the soul
It is easy to recognize that there is nothing in us which we must attribute to our soul except our
thoughts. These are of two principal kinds, some being actions of the soul and others its passions.
Those I call its actions are all our volitions, for we experience them as proceeding directly from
our soul and as seeming to depend on it alone. On the other hand, the various perceptions or
modes of knowledge present in us may be called its passions, in a general sense, for it is often
not our soul which makes them such as they are, and the soul always receives them from the
things that are represented by them.
18. The will
Our volitions, in turn, are of two sorts. One consists of the actions of the soul which terminate in
the soul itself. The other consists of actions which terminate in our body.
19. Perception
Our perceptions are likewise of two sorts: some have the soul as their cause, others the body.
20. Imaginings and other thoughts formed by the soul
When our soul applies itself to imagine something non-existent and also when it applies itself to
consider something that is purely intelligible and imaginable the perceptions it has of these
things depend chiefly on the volition which makes it aware of them. That is why we usually
regard these perceptions as actions rather than passions.
21. Imaginings which are caused solely by the body
, Among the perceptions caused by the body, most of them depend on the nerves. But there are
some which do not and which, like those I have just described are called ‘imaginings’. Theses
differ from the others, however, in that our will is not used in forming them. Before we can
characterize them satisfactorily we must consider how these other perceptions differ from one
another.
22. How these other perceptions differ from one another
They differ from one another in so far as we refer some to external objects which strike our
senses, others to our body or to certain of its parts, and still others to our soul.
23. The perceptions we refer to objects outside us
The perceptions we refer to things outside us, namely to the objects of our senses, are caused by
these objects, at least when our judgements are not false. For in that case the objects produce
certain movements in the organs of the external senses and, by means of the nerves, produce
other movements in the brain, which cause the soul to have sensory perception of the objects.
24. The perceptions we refer to our body
The perceptions we refer to our body or to certain of its parts are those of hunger, thirst, and
other natural appetites. To these we may add pain, heat and other states we feel as being in our
limbs.
25. The perceptions we refer to our soul
The perceptions we refer only to the soul are those whose effects we feel as being in the soul
itself, and for which we do not normally know any proximate cause to which we can refer them.
(e.g. feelings)
26. The imaginings which depend solely on the fortuitous movement of the spirits may be
passions just as truly as the perceptions which depend on the nerves
It remains to be noted that everything the soul perceives by means of the nerves may also be
represented to it through the fortuitous course of the spirits. The sole difference is that the
impressions which come into the brain through the nerves are normally more lively and more
definite than those produced there by the spirits. We must also note that this picture is
sometimes so similar to the thing it represents that it may mislead us regarding the perceptions
which refer to objects outside us, or even regarding those which refer to certain parts of our
body. But we cannot be misled in the same way regarding the passions, in that they are so close
and so internal to our soul that it cannot possibly feel them unless they are truly as it feels them
to be.
27. Definition of the passions of the soul
After having considered in what respects the passions of the soul differ from all its other
thoughts, it seems to me that we may define them generally as those perceptions, sensations or
emotions of the soul which we refer to it, and which are caused, maintained and strengthened by
some movement of the spirits.
28. Explanation of the first part of this definition
We may call them ‘perceptions’ if we use this term generally to signify all the thoughts which are
not actions of the soul or volitions, but not if we use it to signify only evident knowledge. We may
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