The usual order would have been simple. Publish a book. Wait for somebody to object. Answer them in another book. The exchange might take years and occupy several volumes.

Descartes arranged things differently. The objections were invited before the book went to press.

A letter that begins with a complaint

The Fourth Objections were written by Antoine Arnauld. They begin with a letter to Mersenne, and the letter begins by complaining: you would not give me this favour for nothing. You demanded a substantial payment—my opinion of the book—as the price of letting me read it.

Arnauld then announces two roles. First he will speak as a philosopher, then as a theologian. One critic, two declared capacities. At the end he adds that if the result is unsatisfactory, Mersenne must take the blame: Mersenne made him do it.

That letter, complaints included, was printed in Descartes’ own volume.

Why the author wanted them

Descartes explains his purpose in the preface to the reader. First he will set out his thoughts in the meditations, to test whether the reasons that convinced him can convince someone else. Then he will answer objections from learned readers who examined the manuscript before publication.

Next comes the tightening of the claim. The objections are so numerous and varied that he ventures to hope any important difficulty another reader might raise has probably already occurred to these critics. He asks readers to withhold judgment until they have read the objections and replies as well.

On that reckoning, a critic’s strength matters twice. It lends weight to what the critic challenges, and it lends some weight to what the critic leaves unchallenged. A deliberately gentle report would be useless for the second purpose: silence from someone who is holding back tells you very little.

Two more uses of the same move

At the beginning of the Fourth Replies, Descartes makes the point personally. Arnauld has pressed him hard enough that nobody need suspect indulgence. Descartes therefore takes less concern from the objections than satisfaction from the many things Arnauld did not object to.

In the Fifth Replies he turns the thought around. Gassendi, he says, seems less to refute the arguments than to evade their force through rhetorical ingenuity. Even that is useful. Given Gassendi’s ability and diligence, it suggests that genuinely new objections are not easy to find. Gassendi has read the preceding sets; had there been a different strong argument available, he would hardly have missed it.

This is not a charge of stupidity. The critic must be intelligent for the inference to work. An able opponent’s failure to produce a new reason is itself made into information.

In the preface, the test is the number and variety of the critics. With Arnauld, it is the severity of one reader. With Gassendi, it is one reader’s ingenuity. Each time, the opponent’s strength is converted into evidence on the author’s side.

But for that conversion to carry weight, the opponent must really be formidable—and the reader must be able to see it. The objections have to be printed. Simply announcing that the book survived examination is not enough. The examination itself must be on the page, where readers can decide how demanding it was.

The things nobody marked

You give someone a draft and ask for criticism. They oblige, and they are not gentle. You argue over the marked passages: this objection is mistaken; that one rests on a misunderstanding. Afterwards, you feel some relief.

There is another account to reckon with: everything they left unmarked. It does not sting, has no visible outline, and requires no reply, so it is easy to treat it as nothing. Yet a passage scrutinized by a serious critic without provoking an objection may tell you something.

How much it tells you depends on how far those eyes actually travelled. Someone who read only Chapter One tells you nothing by failing to complain about Chapter Five.

At the end

Inside the main text, a man sits by the fire and thinks over successive days. Outside it, a manuscript circulates, people attack it, and author and opponents are bound into the same volume. The exchanges occupy far more space than the initial meditations.

Descartes offers his own assessment: the important objections have probably been raised already. He also prints the material with which a reader might challenge that assessment.