The Animal Spirits

The animal spirits ordinarily go into the traces of the ideas that are most familiar to us, which causes us not to judge things soundly.

I have explained the changes that occur in the animal spirits, and in the constitution of the fibers of the brain, according to the different ages.

Thus, provided one meditates a little on what I have said about them, one will soon have a sufficiently distinct knowledge of the imagination and of the most ordinary physical causes of the differences that are observed between minds; since all the changes that occur in the imagination and in the mind are only consequences of those that occur in the animal spirits and in the fibers of which the brain is composed.

But there are several particular causes, which might be called moral, of the changes that occur in men’s imagination — namely, their different conditions, their different employments, in a word, their different manner of living — to the consideration of which one must apply oneself; because these sorts of changes are the cause of an almost infinite number of errors, each person judging things in relation to his condition.

One does not think one should stop to explain the effects of some less ordinary causes, such as great illnesses, surprising misfortunes, and other unexpected accidents, which make very violent impressions in the brain, and even overturn it entirely, because these things happen rarely; and the errors into which these sorts of persons fall are so gross that they are not contagious, since everyone recognizes them without difficulty.

In order to understand perfectly all the changes that different conditions produce in the imagination, it is absolutely necessary to remember that we imagine objects only by forming images of them; and that these images are nothing other than the traces that the animal spirits make in the brain; that we imagine things the more strongly as these traces are deeper and better engraved, and as the animal spirits have passed through them more often and with more violence; and that when the spirits have passed through them several times, they enter them with more ease than into other nearby places through which they have never passed, or through which they have not passed so often. This is the most ordinary cause of the confusion and falsity of our ideas. For the animal spirits, which have been directed by the action of external objects, or even by the orders of the soul, to produce certain traces in the brain, often produce others that truly resemble them in some way, but which are not entirely the traces of those same objects, nor those that the soul wished to represent to itself; because the animal spirits, finding some resistance in the places of the brain through which they had to pass, easily turn aside to enter in crowds into the deep traces of ideas that are more familiar to us. Here are very gross and very perceptible examples of all this.

When those who have somewhat short sight look at the moon, they ordinarily see there two eyes, a nose, a mouth — in a word, it seems to them that they see a face there. However, there is nothing in the moon of what they think they see. Several persons see something quite different there. And those who believe that the moon is as it appears to them will easily undeceive themselves if they look at it with telescopes, however small they may be; or if they consult the descriptions that Hevelius, Riccioli, and others have given to the public. Now the reason why one ordinarily sees a face in the moon, and not the irregular spots that are there, is that the traces of a face that are in our brain are very deep, because we often look at faces and with much attention. So that the animal spirits, finding resistance in the other places of the brain, easily turn aside from the direction that the light of the moon imprints upon them when one looks at it, to enter into those traces to which the ideas of a face are attached by nature. Besides, the apparent size of the moon not being very different from that of an ordinary head at a certain distance, it forms by its impression traces that have much connection with those that represent a nose, a mouth, and eyes, and thus it determines the spirits to take their course in the traces of a face. There are some who see in the moon a man on horseback, or something other than a face; because their imagination having been vividly struck by certain objects, the traces of these objects are reopened by the least thing that relates to them.

It is also for this same reason that we imagine we see chariots, men, lions, or other animals in the clouds, when there is some slight resemblance between their shapes and these animals; and that everyone, and principally those who are accustomed to drawing, sometimes see men’s heads on walls where there are several irregular spots.

It is also for this reason that spirits of wine, entering without direction of the will into the most familiar traces, cause secrets of the greatest importance to be disclosed; and that when one sleeps, one ordinarily dreams of the objects one has seen during the day, which have formed greater traces in the brain, because the soul always represents to itself the things of which it has greater and deeper traces. Here are other more complex examples.

A disease is new: it causes ravages that surprise the world. This imprints traces so deep in the brain that this disease is always present to the mind. If this disease is called, for example, scurvy, all diseases will be scurvy. Scurvy is new, all new diseases will be scurvy. Scurvy is accompanied by a dozen symptoms, many of which will be common to other diseases; that does not matter. If it happens that a sick person has some one of these symptoms, he will be sick with scurvy; and one will not think at all of the other diseases that have the same symptoms. One will expect that all the accidents that happened to those one has seen sick with scurvy will happen to him as well. One will give him the same medicines, and one will be surprised that they do not have the same effect that one saw in the others.

An author applies himself to a genre of study; the traces of the subject of his occupation imprint themselves so deeply, and radiate so vividly throughout his brain, that they confuse and sometimes efface the traces of things even very different. There was one, for example, who made several volumes on the cross: this made him see crosses everywhere; and it is with reason that Father Morin ridicules him for believing that a medal represented a cross, although it represented something quite different. It is by a similar turn of imagination that Gilbert, and several others, after having studied the magnet and admired its properties, wished to refer a very great number of natural effects to magnetic qualities, which have not the least relation to them.

The examples just brought forward suffice to prove that this great facility that the imagination has to represent to itself objects that are familiar to it, and the difficulty it experiences in imagining those that are new to it, causes men almost always to form ideas that may be called mixed and impure; and that the mind judges things only in relation to itself and to its first thoughts. Thus, the different passions of men, their inclinations, their conditions, their employments, their qualities, their studies — finally, all their different manners of living — putting very great differences in their ideas, cause them to fall into an infinite number of errors, which we shall explain in what follows. And this is what made Chancellor Bacon say these very judicious words: Omnes perceptiones tam sensus quam mentis sunt ex analogia hominis, non ex analogia universi; estque intellectus humanus instar speculi inaequalis ad radios rerum qui suam naturam naturae rerum immiscet, eamque distorquet, et inficit. [All perceptions, both of sense and of mind, are according to the analogy of man, not according to the analogy of the universe; and the human intellect is like an uneven mirror to the rays of things, which mixes its own nature with the nature of things, and distorts and infects it.]