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.