The senses deceive from time to time, and it is prudent never to trust wholly those who have deceived us even once.

Everything is self-evident.

The rainbow is such a remarkable phenomenon of nature, and its cause has been so meticulously sought after by inquiring minds throughout the ages, that I could not choose a more appropriate subject for demonstrating how, with the method I am using, we can arrive at knowledge not possessed at all by those whose writings are available to us.

And I shall always hold myself more obliged to those by whose favour I enjoy uninterrupted leisure than to any who might offer me the most honourable positions in the world.

Situations in life often permit no delay; and when we cannot determine the course which is certainly best, we must follow the one which is probably the best. This frame of mind freed me also from the repentance and remorse commonly felt by those vacillating individuals who are always seeking as worthwhile things which they later judge to be bad.

The only thing we have power over in the universe is our own thoughts.

I know that I exist; the question is, What is this 'I' that 'I' know.