If the theorem is true of _n_ - 1, so it is of _n_.
We see, then, that in reasoning by recurrence we confine ourselves to
stating the minor of the first syllogism, and the general formula which
contains as particular cases all the majors.
This never-ending series of syllogisms is thus reduced to a phrase of a
few lines.
It is now easy to comprehend why every particular consequence of a
theorem can, as I have explained above, be verified by purely analytic
procedures.
If instead of showing that our theorem is true of all numbers, we only
wish to show it true of the number 6, for example, it will suffice for
us to establish the first 5 syllogisms of our cascade; 9 would be
necessary if we wished to prove the theorem for the number 10; more
would be needed for a larger number; but, however great this number
might be, we should always end by reaching it, and the analytic
verification would be possible.
And yet, however far we thus might go, we could never rise to the
general theorem, applicable to all numbers, which alone can be the
object of science. To reach this, an infinity of syllogisms would be
necessary; it would be necessary to overleap an abyss that the patience
of the analyst, restricted to the resources of formal logic alone, never
could fill up.
I asked at the outset why one could not conceive of a mind sufficiently
powerful to perceive at a glance the whole body of mathematical truths.
The answer is now easy; a chess-player is able to combine four moves,
five moves, in advance, but, however extraordinary he may be, he will
never prepare more than a finite number of them; if he applies his
faculties to arithmetic, he will not be able to perceive its general
truths by a single direct intuition; to arrive at the smallest theorem
he can not dispense with the aid of reasoning by recurrence, for this is
an instrument which enables us to pass from the finite to the infinite.
This instrument is always useful, for, allowing us to overleap at a
bound as many stages as we wish, it spares us verifications, long,
irksome and monotonous, which would quickly become impracticable. But it
becomes indispensable as soon as we aim at the general theorem, to which
analytic verification would bring us continually nearer without ever
enabling us to reach it.
In this domain of arithmetic, we may think ourselves very far from the
infinitesimal analysis, and yet, as we have just seen, the idea of the
mathematical infinite already plays a preponderant rôle, and without it
there would be no science, because there would be nothing general.
VI
The judgment on which reasoning by recurrence rests can be put under
other forms; we may say, for example, that in an infinite collection of
different whole numbers there is always one which is less than all the
others.
Public-domain text, read in full here on John Shaqi.
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