It is... easy to be certain. One has only to be sufficiently vague.

True science is distinctively the study of useless things. For the useful things will get studied without the aid of scientific men. To employ these rare minds on such work is like running a steam engine by burning diamonds.

Theology, I am persuaded, derives its initial impulse from a religious wavering; for there is quite as much, or more, that is mysterious and calculated to awaken scientific curiosity in the intercourse with God, and it [is] a problem quite analogous to that of theology.

It is a common observation that those who dwell continually upon their expectations are apt to become oblivious to the requirements of their actual situation.

Mathematics is purely hypothetical: it produces nothing but conditional propositions.

It has often been argued that absolute scepticism is self-contradictory; but this is a mistake: and even if it were not so, it would be no argument against the absolute sceptic, inasmuch as he does not admit that no contradictory propositions are true. Indeed, it would be impossible to move such a man, for his scepticism consists in considering every argument and never deciding upon its validity; he would, therefore, act in this way in reference to the arguments brought against him.

All the progress we have made in philosophy ... is the result of that methodical skepticism which is the element of human freedom.