He begins by carefully eliminating all the episodes which, though
apparently premonitory, may be explained by self-suggestion (as
in the case, for instance, where some one smitten with a disease
still latent seems to foresee this disease and the death which
will be its conclusion), by telepathy (when a sensitive is aware
beforehand of the arrival of a person or a letter), or lastly by
clairvoyance (when a man dreams of a spot where he will find
something which he has mislaid, or an uncommon plant, or an
insect sought for in vain, or of the unknown place which he will
visit at some later date).

In all these cases, we have not, properly speaking, to do with a
pure future, but rather with a present that is not yet known.
Thus reduced and stripped of all foreign influences and
intrusions the number of instances in which there is a really
clear and incontestable perception of a fragment of the future
remains large enough, contrary to what is generally believed, to
make it impossible for us to speak of extraordinary accidents or
wonderful coincidences. There must be a limit to everything, even
to distrust, even to the most extensive incredulity, otherwise
all historical research and a good deal of scientific research
would become decidedly impracticable. And this remark applies as
much to the nature of the incidents related as to the actual
authenticity of the narratives. We can contest or suspect any
story whatever, any written proof, any evidence; but
thenceforward we must abandon all certainty or knowledge that is
not acquired by means of mathematical operations or laboratory
experiments, that is to say, three-fourths of the human phenomena
which interest us most. Observe that the records collected by the