In the imagination of those who are sensitive to the realities of our era, the earth has become a space ship, and this, perhaps, is the most importan… - Kenneth E. Boulding

The concept of need is often looked upon rather unfavorably by economists, in contrast with the concept of demand. Both, however, have their own strengths and weaknesses. The need concept is criticized as being too mechanical, as denying the autonomy and individuality of the human person, and as implying that the human being is a machine which "needs" fuel in the shape of food, engine dope in the shape of medicine, and spare parts provided by the surgeon.

[The theory of the firm] is exactly analogous to the analysis of the reactions of a consumer by means of indifferent curves. Indeed, a consumer is merely a ‘firm’ whose product is ‘utility’.

What I have been talking about is knowledge. Knowledge, perhaps, is not a good word for this. Perhaps one would rather say my image of the world. Knowledge has an implication of validity, of truth. What I am talking about is what I believe to be true; my subjective knowledge. It is this Image that largely governs my behavior. In about an hour I shall rise, leave my office, go to a car, drive down to my home, play with the children, have supper, perhaps read a book, go to bed. I can predict this behavior with a fair degree to accuracy because of the knowledge which I have: the knowledge that I have a home not far away, to which I am accustomed to go. The prediction, of course, may not be fulfilled. There may be an earthquake, I may have an accident with the car on the way home, I may get home to find that my family has been suddenly called away. A hundred and one things may happen. As each event occurs, however, it alters my knowledge structure or my image. And as it alters my image, I behave accordingly. The first proposition of this work, therefore, is that behavior depends on the image.