[2] We here put out of sight all questions connected with the changing purchasing power of money. This is, in ordinary times, the business man's habit. He considers his capital intact if the number of dollars invested originally in his business still appears on his inventory as representing the net surplus of his assets over his liabilities. If a currency were undergoing rapid inflation, a fixed amount of invested money would represent a shrinking stock of capital goods. This stock would last always, but would grow smaller by a true standard of measurement. All that we are at present interested in knowing is that practical usage treats capital as a permanent fund of productive wealth, and most conveniently describes it as a fixed amount of money "invested" in goods of a productive kind. What is thought of as "money" abides. Of course the practical man does not regard it as actually composed of currency. _The Chief Attribute of Capital._--A chief attribute of capital, properly so called, is permanence. If a man's productive fund does not last, he is impoverished. The farmer keeps on hand a more or less constant supply of the implements he has to use. He takes a part of the proceeds of the sale of his crops, puts it into the shape of implements and materials, and in this way keeps an amount of them on hand as the auxiliary capital of agriculture. Particular goods are not constant, but the sum of money or quantum of wealth "invested" in the moving procession of them is so. At any one instant the capital is composed of particular instruments which can be sought out and identified, but at no two instants are the goods the same. _The Reasons for describing Capital as a Sum of Money._--This fact explains the general practice of describing capital in terms of money. The manufacturer just referred to will speak of his capital as "a million dollars" and consider that sum as a "permanent investment" because he knows that while the goods that now represent that value will soon pass from him, the "dollars"--that is, the value which is equivalent to the dollars--will abide. There is, moreover, no failure on his part to discriminate between his capital and literal money, for he knows in what his productive fund consists, and is fully aware that only the minutest part of it is in the shape of actual currency. Instruments of production compose the fund, but the dollars serve to describe it. They indicate the amount and the abiding quality of it, since they describe what he has invested or embodied in the shifting things and can, by a fair sale, get out of them.