In conclusion I wish to say that in working at the problem here dealt with I have had the loyal assistance of my friend and colleague M. Besso, and that I am indebted to him for several valuable suggestions.

The most evident difference springs from the important part which is played in man by a relatively strong power of imagination and by the capacity to think, aided as it is by language and other symbolically devices.

Out of complexity, find simplicity!

If tomorrow were never to come, it would not be worth living today.

Scientists investigate that which already is; Engineers create that which has never been.

To have a better life we must keep choosing how we are living.

The moon does not simply disappear when we are not looking at it.