This Day in Philosophy — 19 August: the death of Blaise Pascal

Blaise Pascal died in Paris on 19 August 1662, at the age of thirty-nine. Into that short life he fitted work in mathematics, physics and philosophy that looks, at first, unconnected.

Mathematics and a machine#

At sixteen Pascal wrote a treatise on conic sections. In his twenties he designed a mechanical calculator to ease the accounts of his father, a tax official. His experiments on the vacuum and air pressure unsettled the age's principle that nature abhors a vacuum.

His correspondence with Pierre de Fermat counts among the founding texts of probability theory. Arising from a question about gambling, that exchange made decision under uncertainty a subject for mathematics.

The wager#

Pascal's most argued-over philosophical argument grows out of exactly that thought about probability. The wager (le pari) does not try to prove the existence of God; it begins by accepting that proof is impossible.

The structure of the argument is a decision problem: if reason cannot settle the question, we still have to live, and in living we take a side. Pascal compares the possible gains and losses. Read today in the language of decision theory, the argument appears as an early instance of expected-utility reasoning — which is why it interests economists and decision theorists more than theologians.

A common misreading is that the wager says "you can choose to believe". Pascal knows belief cannot be produced by an act of will; his proposal is that a person put themselves into a way of living that leaves them open to belief.

The reasons of the heart#

The Pensées were compiled from the notes Pascal kept for an apologetic book he never finished. Fragmentary, sometimes a single sentence long, the text is counted among the summits of French prose despite its formal disorder.

Its best-known sentence is there: "The heart has its reasons, which reason does not know."

The sentence is often used as an anti-rationalist slogan; what Pascal says is subtler. First principles — space, time, number — are not known by proof but grasped directly. Reason builds its proofs on those direct apprehensions. The heart is not reason's enemy but its foundation.

Between two infinities#

Pascal's picture of the human follows from this: a being suspended between the infinitely large and the infinitely small, unable to grasp its own position. Yet within that weakness it carries a privilege — it is "a thinking reed". The universe can crush it; but the universe does not know that it crushes, and the reed does.