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like the solidification of liquids, and like all changes of state, it presents its own obstacles.
If we take these considerations into account, we see that having no objective base, the calculation
of probabilities is applicable to an actual subjective quantity, which, however, it cannot measure. To
me the major merit of calculation is to show clearly that the quantity is indeed measurable. If one must
absolutely have an objective foundation, it can only be a greater or lesser tendency of future events to
take place. But how can we conceive of this tendency if not as a type of desire? This calculation is
thus necessarily based on the hypothesis that desire is measurable, if not belief.
At election time one sees candidates’ hopes and fears rise and fall several times in the same day as
a consequence of the slightest new information or the most insignificant gossip. The calculation of
probabilities certainly plays no role here. But what is very clear is the markedly quantitative
character of these hopes and fears. As time passes, and without any calculation of the probabilities,
each of us senses in himself a fairly regular decline of confidence in our memories, and a word
suffices to arouse or trouble us. When we see one of our friends in the distance and we are uncertain
at first whether or not it is he, we feel, as he comes closer, a regular increase in our belief in the
reality of his presence. Here again calculation of probabilities is neither possible nor imaginable. I
believe, however, that these are quantitative variations just like the rise or fall of temperature. One
cannot thus claim that measurability is a property that belief borrows from the language of
calculation, since measurability persists after calculation is forced into silence.
Certainly the grossest method of measuring internal qualities (though the one which seems most
rigorous) would be to express them by the quantity of action which exhausts a desire or realizes an
idea every time that such an action is made of gestures, movements, expenditures of muscular force,
all reducible to quantities of molecular movements. One would say that the thirst satisfied by one
glass of water is equal to half of that which requires two glasses of water to be quenched, and so
forth.
Though difficult to discover, an approximate measure of even individual beliefs and desires would
eventually have been thought up if most men had felt its need as strongly as the need of a measure of
opinion or general inclination. But unfortunately in practical life the degree of an individual opinion
or inclination is not important, or rather is of no interest; consequently no one observes that an
opinion has degrees. For the same reason, according to the law formulated by Helmholtz in his
Optics, visual phenomena that, although visible, are useless with respect to practical knowledge of
objects (flies in flight, accidental images) are simply not seen except perhaps by the sick or by
occulists. Similarly it is only psychologists who pay attention to their nascent ideas or sentiments, to
slight disturbances, and to the slow decay of their religious and political faiths, to their affections and
their loves. The practical man is not aware of such breakdowns until the completed ruin returns his
freedom of action to him. A desire, like an opinion, can be used to manage public or private business,
by vote or notarized act, only if it is considered absolute and not relative. The man of action appears
to give himself completely to everything he undertakes and, indeed, he believes he does so—a
situation having many drawbacks. A court doctor is not asked, “Are you entirely, almost, threequarters,
one-half convinced that there was poisoning? Do you believe this as strongly as you believe
in the existence of Theseus, or of Romulus, or in the existence of Tarquin the Proud, or that of Louis
XIV, or that of your father?”; he is asked instead, “Was there or was there not poisoning?” And most
of the time when the court doctor replies to this question, he implicitly makes a certainty of something
about which he is still to some degree doubtful.
An all too infrequent mark of philosophical honesty is the attempt to render exactly not only the
precise nuance of one’s thought but the level of confidence (le “taux” de confiance) one has in it. The