What exists, is possible.

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

As far as many statistical series that are related to activities of mankind are concerned, the date that divides human history into two equal parts is well within living memory. The world of today is as different from the world I was born in as that world was from Julius Caesar s. I was born in the middle of human history, to date, roughly. Almost as much has happened since I was born as happened before.

There are, of course, a number of epistemological questions, some of which lie more in the province of the philosopher than they do the economist or the social scientist. The one with which I am particularly concerned here is that of the role of knowledge in social systems, both as a product of the past and as a determinant of the future.

Mathematicians themselves set up standards of generality and elegance in their exposition which are a bar to understand.

What exists, is possible.

The discounting presumably is to be done for each period of time at that rate of interest which represents the alternative cost of employing capital in the occupation in question; that is, at the rate which the entrepreneur could obtain in other investments