146 THE GENERAL THEORY OF EMPLOYMENT BK. IV

current phenomenon; and if we reduce the marginalefficiency of capital to the same status, we cut our-selves off from taking any direct account of the in-fluence of the future in our analysis of the existingequilibrium.

The fact that the assumptions of the static stateoften underlie present-day economic theory, importsinto it a large element of unreality. But the introduc-tion of the concepts of user cost and of the marginalefficiency of capital, as defined above, will have theeffect, I think, of bringing it back to reality, whilstreducing to a minimum the necessary degree of adapta-tion.

It is by reason of the existence of durable equipmentthat the economic future is linked to the present. It is,therefore, consonant with, and agreeable to, our broadprinciples of thought, that the expectation of the futureshould affect the present through the demand price fordurable equipment.