One advantage of exhibiting a hierarchy of systems in this way is that it gives us some idea of the present gaps in both theoretical and empirical knowledge. Adequate theoretical models extend up to about the fourth level, and not much beyond. Empirical knowledge is deficient at practically all levels.

If we saw tomorrow's newspaper today, tomorrow would never happen.

If the society toward which we are developing is not to be a nightmare of exhaustion, we must use the interlude of the present era to develop a new technology which is based on a circular flow of materials such that the only sources of man's provisions will be his own waste products.

We are born to love, as we are born to breathe and eat and drink.

Deciding under uncertainty is bad enough, but deciding under an illusion of certainty is catastrophic.

The World is a very complex system. It is easy to have too simple a view of it, and it is easy to do harm and to make things worse under the impulse to do good and make things better.

Physicists only talk to physicists, economists to economists-worse still, nuclear physicists only talk to nuclear physicists and econometricians to econometricians. One wonders sometimes if science will not grind to a stop in an assemblage of walled-in hermits, each mumbling to himself words in a private language that only he can understand.