There is only one road to human greatness: through the school of hard knocks.

It is my conviction that pure mathematical construction enables us to discover the concepts and the laws connecting them, which gives us the key to the understanding of nature ... In a certain sense, therefore, I hold it true that pure thought can grasp reality, as the ancients dreamed.

I made one great mistake in my life-when I signed the letter to President Roosevelt recommending that atom bombs be made but there was some justification-the danger that the Germans would make them.

(Reply on what constitutes scientific proof:)"The question is much too difficult for me.

I am fascinated by Spinoza's pantheism, but admire even more his contributions to modern thought because he is the first philosopher to deal with the soul and the body as one, not two separate things

Everything that exists in your life, does so because of two things: something you did or something you didn't do.

How was I able to live alone before, my little everything? Without you I lack self-confidence, passion for work, and enjoyment of life--in short, without you, my life is no life. [Written to his wife, Mileva]