Some years ago I was struck by the large number of falsehoods that I had accepted as true in my childhood, and by the highly doubtful nature of the whole edifice that I had subsequently based on them. I realized that it was necessary, once in the course of my life, to demolish everything completely and start again right from the foundations if I wanted to establish anything at all in the sciences that was stable and likely to last.

Sensations are nothing but confused modes of thinking.

In order to improve the mind, we ought less to learn, than to contemplate.

When writing about transcendental issues, be transcendentally clear.

Even those who have the weakest souls could acquire absolute mastery over all their passions if we employed sufficient ingenuity in training and guiding them.

Doubt is the origin of wisdom

If you would be a real seeker after truth, it is necessary that at least once in your life you doubt, as far as possible, all things.