acing myself in the
same case with that which I consider, 'tis evident this reflection
and premeditation would so disturb the operation of my natural
principles, as must render it impossible to form any just
conclusion from the phenomenon. We must, therefore, glean up our
experiments in this science from a cautious observation of human
life, and take them as they appear in the common course of the
world, by men's behaviour in company, in affairs, and in their
pleasures. Where experiments of this kind are judiciously collected
and compared, we may hope to establish on them a science which
will not be inferior in certainty, and will be much superior in
utility, to any other of human comprehension."--(I. pp. 7-11.)

All science starts with hypotheses--in other words, with assumptions
that are unproved, while they may be, and often are, erroneous; but
which are better than nothing to the seeker after order in the maze of
phenomena. And the historical progress of every science depends on the
criticism of hypotheses--on the gradual stripping off, that is, of their
untrue or superfluous parts--until there remains only that exact verbal
expression of as much as we know of the fact, and no more, which
constitutes a perfect scientific theory.

Philosophy has followed the same course as other branches of scientific
investigation. The memorable service rendered to the cause of sound
thinking by Descartes consisted in this: that he laid the foundation of
modern philosophical criticism by his inquiry into the nature of
certainty. It is a clear result of the investigation started by
Descartes, that there is one thing of which no doubt can be entertained,
for he who should pretend to doubt it would thereby prove its existence;
and that is the momentary consciousness we call a present thought or
feeling; that is safe, even if all other kinds of certainty are merely
more or less probable inferences. Berkeley and Locke, each in his way,
applied philosophical criticism in other directions; but they always, at
any rate professedly, followed the Cartesian maxim of admitting no
propositions to be true but such as are clear, distinct, and evident,
even while their arguments stripped off many a layer of hypothetical
assumption which their great predecessor had left untouched. No one has
more clearly stated the aims of the critical philosopher than Locke, in
a passage of the famous _Essay c