Maintain a constant watch at all times against a dogmatical spirit: fix not your assent to any proposition in a firm and unalterable manner, till you have some firm and unalterable ground for it, and till you have arrived at some clear and sure evidence. The Improvement of the Mind (1727)
Once a day, especially in the early years of life and study, call yourselves to an account what new ideas, what new proposition or truth you have gained, what further confirmation of known truths, and what advances you have made in any part of knowledge; and let no day, if possible, pass away without some intellectual gain. The Improvement of the Mind (1727)