I soon became convinced... that all the theorizing would be empty brain exercise and therefore a waste of time unless one first ascertained what the population of the universe really consists of.

He who lives in the single exercise of his mental faculties, however usefully or curiously directed, is equally an imperfect animal with the man who knows only the exercise of muscles.

In fact, it is a farce to call any being virtuous whose virtues do not result from the exercise of its own reason.

But I work harder now because I have so much more exposure. And actually the harder you work as a writer, the better you get at it. It's like anything else. It's a muscle you have to exercise. I write more now than ever.

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.

I think if people value democracy, they had damn well better get out and exercise their right to vote while their vote still means something.

It's a remarkable exercise to sit and look at your own work over the years.

If you exercise your mind, you're not going to get sick.

If I've got food and water, as long as I can exercise my mind and keep it nimble, then I'll be okay.

It can become an exercise in trying to get the reader to like and admire you instead of an exercise in creative art.

In terms of fitness and battling through cancer, exercise helps you stay strong physically and mentally.

It is the spirit of the age to believe that any fact, no matter how suspect, is superior to any imaginative exercise, no matter how true.

An obituary should be an exercise in contemporary history, not a funeral oration.

I have never taken any exercise except sleeping and resting.

Mathematical reasoning may be regarded rather schematically as the exercise of a combination of two facilities, which we may call intuition and ingenuity.