William Whewell

We cannot observe external things without some degree of Thought; nor can we reflect upon our Thoughts, without being influenced in the course of our reflection by the Things which we have observed.

Every failure is a step to success.

Fundamental ideas are not a consequence of experience, but a result of the particular constitution and activity of the mind, which is independent of all experience in its origin, though constantly combined with experience in its exercise.

Geometry in every proposition speaks a language which experience never dares to utter and indeed of which she but halfway comprehends the meaning.

The question undoubtedly is or soon will be not whether or no we shall employ notation in chemistry but whether we shall use a bad and incongruous or a consistent and regular notation.

Prudence supposes the value of the end to be assumed, and refers only to the adaptation of the means. It is the relation of right means for given ends.

It is a test of true theories not only to account for but to predict phenomena.

The system becomes more coherent as it is further extended. The elements which we require for explaining a new class of facts are already contained in our system. In false theories, the contrary is the case.

Hence no force, however great, can stretch a cord, however fine, into a horizontal line which is accurately straight: there will always be a bending downwards.