Two other examples

It is certain that the primary cause of most of our errors is this strong application of the soul to what comes to it through the senses, and this negligence it shows toward the things that pure understanding represents to it. An example of great consequence for morals has just been given, drawn from human conversation; here are others drawn from the commerce we have with the rest of nature, which it is absolutely necessary to remark for physics.

The first, concerning our errors regarding the nature of bodies

One of the principal errors into which one falls in matters of physics is imagining that there is much more substance in bodies that make themselves strongly felt than in others that are hardly felt at all. Most men believe that there is far more matter in gold and lead than in air and water; and even children, who have not noticed the effects of air through the senses, usually imagine that it is nothing real.

Gold and lead are very heavy, very hard, and very sensible; water and air, on the contrary, are hardly felt at all. From this, men conclude that the former have much more reality than the latter, or that there is more matter in a cubic foot of gold than in a cubic foot of air. They judge the truth of things by the sensible impression, which always deceives us, and they neglect the clear and distinct ideas of the mind, which never deceive us, because the sensible touches and engages us, while the intelligible puts us to sleep. These false judgments concern the substance of bodies; here are others concerning the qualities of the same bodies.

The second, concerning those regarding the qualities of these same bodies.

Men almost always judge that the objects which excite in them more pleasant sensations are the most perfect and the purest, without knowing even in what the perfection and purity of matter consist, and without even troubling themselves about it.

They say, for example, that mud is impure and that very clear water is very pure. But camels, which like muddy water, and those animals that delight in mud, would not share their opinion. They are beasts, it is true. But people who love the entrails of the woodcock and the excrement of the polecat do not say that it is impurity, although they say so of what comes from all other animals. Finally, musk and amber are generally esteemed by all men, even by those who believe they are nothing but excrements.

Certainly, one judges the perfection of matter and its purity only in relation to one’s own senses; and from this it happens that, since the senses are different in all men, as has been sufficiently explained, they must judge very diversely of the perfection and purity of matter. Thus, the books they compose every day on the imaginary perfections they attribute to certain bodies are necessarily filled with errors of a quite strange and bizarre variety, since the reasonings they contain are supported only by the false, confused, and irregular ideas of our senses.

Philosophers must not say that matter is pure or impure if they do not know precisely what they mean by these words pure and impure; for one must not speak without knowing what one is saying—that is, without having distinct ideas corresponding to the terms one uses. Now, if they had attached clear and distinct ideas to each of these words, they would see that what they call pure would often be very impure, and that what appears to them impure would often be found very pure.

If, for example, they wished that matter were most pure and perfect whose parts were the finest and easiest to move, gold, silver, and precious stones would be extremely imperfect bodies, and air and fire, on the contrary, would be very perfect. When flesh came to corrupt and smell bad, it would then begin to perfect itself, and a stinking carcass would be a much more perfect body than ordinary flesh.

If, on the contrary, they wished that the most perfect bodies were those whose parts were the largest, most solid, and most difficult to move, earth would be more perfect than gold, and air and fire would be the most imperfect bodies.

If one does not wish to attach to the terms pure and perfect the distinct ideas I have just mentioned, it is permissible to substitute others in their place. But if one pretends to define these words only by sensible notions, one will eternally confuse all things, since one will never fix the meaning of the terms that express them. All men, as has already been proved, have very different sensations of the same objects; therefore, one must not define these objects by the sensations one has of them, if one does not wish to speak without being understood and to create confusion everywhere.

But fundamentally, I do not see that there is any matter, even that of which the heavens are composed, which contains in itself more perfection than others. All matter seems capable only of figures and motions, and it is indifferent to it whether it has regular or irregular figures and motions. Reason does not tell us that the sun is more perfect or more luminous than mud, nor that these beauties of our novels and poets have any advantage over the most corrupted corpses. It is our false and deceptive senses that tell us so. One may cry out as much as one likes; all railleries and exclamations will appear cold and frivolous to those who attentively examine the reasons that have been brought forward.

Those who know only how to feel believe that the sun is full of light; but those who know how to feel and to reason do not believe it, provided they know how to reason as well as they know how to feel. One is fully persuaded that even those who defer most to the testimony of their senses would enter into the sentiment held here if they had well meditated on the things that have been said. But they love too much the illusions of their senses; they have obeyed their prejudices for too long, and their soul has forgotten itself too much to recognize that all the perfections it imagines seeing in bodies belong to itself.

Nor is it to such people that one speaks; one cares little for their approval and esteem: they do not wish to listen, so they cannot judge. It suffices that one defends the truth and has the approval of those who work seriously to deliver themselves from the errors of their senses and to make good use of the lights of their mind. One asks only that they meditate on these thoughts with as much attention as they can, and that they judge, condemn, or approve them. One submits them to their judgment, because by their meditation they have acquired over them the right of life and death, which cannot be contested without injustice.