There is in the true man of science a desire stronger than the wish to have his beliefs upheld; namely, the desire to have them true. - William Kingdon Clifford

We may believe what goes beyond our experience, only when it is inferred from that experience by the assumption that what we do not know is like what we know. We may believe the statement of another person, when there is reasonable ground for supposing that he knows the matter of which he speaks, and that he is speaking the truth so far as he knows it. It is wrong in all cases to believe on insufficient evidence; and where it is presumption to doubt and to investigate, there it is worse than presumption to believe.

Remember, then, that [scientific thought] is the guide of action; that the truth which it arrives at is not that which we can ideally contemplate without error, but that which we may act upon without fear; and you cannot fail to see that scientific thought is not an accompaniment or condition of human progress, but human progress itself. And for this reason the question what its characters are... is the question of all questions for the human race.

No mathematician can give any meaning to language about matter, force, inertia, used in text-books of mechanics.