Every failure is a step to success.
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.
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.
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.
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.