A System of Logic: Ratiocinative and Inductive, 7th Edition, Vol. II — John Stuart Mill — John Shaqi
A System of Logic: Ratiocinative and Inductive, 7th Edition, Vol. II
John Stuart Mill · en
Or suppose a regiment of 1000 men, 999 Englishmen and one Frenchman, and
that of these one man has been killed, and it is not known which. I ask
the question, and the witness answers, the Frenchman. This was not only
as improbable _à priori_, but is in itself as singular a circumstance,
as remarkable a coincidence, as the drawing of the white ball: yet we
should believe the statement as readily, as if the answer had been John
Thompson. Because though the 999 Englishmen were all alike in the point
in which they differed from the Frenchman, they were not, like the 999
black balls, undistinguishable in every other respect; but being all
different, they admitted as many chances of interest or error, as if
each man had been of a different nation; and if a lie was told or a
mistake made, the misstatement was as likely to fall on any Jones or
Thompson of the set, as on the Frenchman.
The example of a coincidence selected by D'Alembert, that of sixes
thrown on a pair of dice ten times in succession, belongs to this sort
of cases rather than to such as Laplace's. The coincidence is here far
more remarkable, because of far rarer occurrence, than the drawing of
the white ball. But though the improbability of its really occurring is
greater, the superior probability of its being announced falsely cannot
be established with the same evidence. The announcement "black"
represented 999 cases, but the witness may not have known this, and if
he did, the 999 cases are so exactly alike, that there is really only
one set of possible causes of mendacity corresponding to the whole. The
announcement "sixes _not_ drawn ten times," represents, and is known by
the witness to represent, a great multitude of contingencies, every one
of which being unlike every other, there may be a different and a fresh
set of causes of mendacity corresponding to each.
It appears to me, therefore, that Laplace's doctrine is not strictly
true of any coincidences, and is wholly inapplicable to most: and that
to know whether a coincidence does or does not require more evidence to
render it credible than an ordinary event, we must refer, in every
instance, to first principles, and estimate afresh what is the
probability that the given testimony would have been delivered in that
instance, supposing the fact which it asserts not to be true.
With these remarks we close the discussion of the Grounds of Disbelief;
and along with it, such exposition as space admits, and as the writer
has it in his power to furnish, of the Logic of Induction.
FOOTNOTES:
[1] _Cours de Philosophie Positive_, ii. 656.
[2] Vide supra, book iii. ch. xi.
[3] _Philosophy of Discovery_, pp. 185 et seqq.
[4] _Philosophie Positive_, ii. 434-437.