One disputes every day if, in war, luck or leadership produces successes.
If, in disease, nature acts more than medicine for curing or killing.
If, in jurisprudence, it is not very advantageous to come to terms when one is in the right, and to plead when one is in the wrong.
If literature contributes to the glory of a nation or to its decadence.
If one should or should not make the people superstitious.
If there is anything true in metaphysics, history and moral philosophy.
If taste is arbitrary, and if there is in fact good taste and bad taste, etc., etc.
To decide all these questions right away, take an example of what is the most extreme in each; compare the two opposed extremes, and you will at once discover which is true.
You wish to know if leadership can infallibly determine the success of the war; look at the most extreme case, the most opposed situations, in which leadership alone will infallibly triumph. The enemy's army is forced to pass through a deep mountain gorge; your general knows it: he makes a forced march, he takes possession of the heights, he holds the enemy shut in a pass; they must either die or surrender. In this extreme case, luck cannot have any part in the victory. It is therefore demonstrated that skill can determine the success of a campaign; from that alone is it proved that war is an art.
Now imagine an advantageous but less decisive position; success is not so certain, but it is always very probable. You arrive thus, step by step, to a perfect equality between the two armies. What will decide then? luck, that is to say an unforeseen event, a general officer killed when he is on his way to execute an important order, a corps which is shaken by a false rumour, a panic and a thousand other cases which cannot be remedied by prudence; but it still remains certain that there is an art, a generalship.
As much must be said of medicine, of this art of operating on the head and the hand, to restore life to a man who is about to lose it.
The first man who at the right moment bled and purged a sufferer from an apoplectic fit; the first man who thought of plunging a knife into the bladder in order to extract a stone, and of closing the wound again; the first man who knew how to stop gangrene in a part of the body, were without a doubt almost divine persons, and did not resemble Moliere's doctors.
Descend from this obvious example to experiments that are less striking and more equivocal; you see fevers, ills of all kinds which are cured, without it being well proved if it be nature or the doctor who has cured them; you see diseases of which the result cannot be guessed; twenty doctors are deceived; the one that has the most intelligence, the surest eye, guesses the character of the malady. There is therefore an art; and the superior man knows the finenesses of it. Thus did La Peyronie guess that a man of the court had swallowed a pointed bone which had caused an ulcer, and put him in danger of death; thus did Boerhaave guess the cause of the malady as unknown as cruel of a count of Vassenaar. There is therefore really an art of medicine; but in all arts there are men like Virgil and Maevius.
In jurisprudence, take a clear case, in which the law speaks clearly; a bill of exchange properly prepared and accepted; the acceptor must be condemned to pay it in every country. There is therefore a useful jurisprudence, although in a thousand cases judgments are arbitrary, to the misfortune of the human race, because the laws are badly made.
Do you desire to know if literature does good to a nation; compare the two extremes, Cicero and an uncouth ignoramus. See if it is Pliny or Attila who caused the fall of Rome.
One asks if one should encourage superstition in the people; see above all what is most extreme in this disastrous matter, St. Bartholomew, the massacres in Ireland, the crusades; the question is soon answered.
Is there any truth in metaphysics? Seize first of all the points that are most astonishing and the most true; something exists for all eternity. An eternal Being exists by Himself; this Being cannot be either wicked or inconsequent. One must surrender to these truths: almost all the rest is given over to dispute, and the justest mind unravels the truth while the others are seeking in the shadows.
It is with all things as with colours; the weakest eyes distinguish black from white; the better, more practised eyes, discern shades that resemble each other.