Alfred Marshall

The most valuable of all capital is that invested in human beings

And thus the law may be worded:— The of a commodity to anyone diminishes with every increase in the amount of it he already has.

The increment of the commodity which he is only just induced to acquire (whether by... direct labor or by purchase) may be called its Marginal Increment; because he is on the margin of doubt whether it is worth his while to incur the …

Political Economy or Economics is a study of mankind in the ordinary business of life; it examines that part of individual and social action which is most closely connected with the attainment and with the use of the material requisites of …