The rational herdsman concludes that the only sensible course for him to pursue is to add another animal to his herd. And another; and another . . . But this is the conclusion reached by each and every rational herdsman sharing a commons. Therein is the tragedy. Each man is locked into a system that compels him to increase his herd without limit — in a world that is limited. Ruin is the destination toward which all men rush, each pursuing his own best interest in a society that believes in the freedom of the commons. Freedom in a commons brings ruin to all.

The morality of an act is a function of the state of the system at the time it is performed.

Never globalize a problem if it can possibly be dealt with locally.

To say that we mutually agree to coercion is not to say that we are required to enjoy it, or even to pretend we enjoy it.

It is a mistake to think that we can control the breeding of mankind in the long run by an appeal to conscience.

A technical solution may be defined as one that requires a change only in the techniques of the natural sciences, demanding little or nothing in the way of change in human values or ideas of morality.

Every plausible policy must be followed by the question 'And then what?'