This statement may at first seem puzzling, for we usually think of causes and effects as running forward not backward in time. It would seem then that income must be derived from capital; and, in a sense, this is true. Income is derived from capital goods. But the value of the income is not derived from the value of the capital goods. On the contrary, the value of the capital is derived from the value of the income. Valuation is a human process in which foresight enters. Coming events cast their shadows before. Our valuations are always anticipations.
These relations are shown in the following scheme in which the arrows represent the order of sequence—(1) from capital goods to their future services, that is, income; (2) from these services to their value; and (3) from their value back to capital value:
Not until we know how much income an item of capital will probably bring us can we set any valuation on that capital at all. It is true that the wheat crop depends on the land which yields it. But the value of the crop does not depend on the value of the land. On the contrary, the value of the land depends on the expected value of its crops.
至此，我想讀者應該弄清楚Irving Fisher的意思了。我們習於順向思考事務，對表象視為理所當然，很少做進一步的思考，Irving Fisher的不同思維方式的確令人為之擊節讚賞，值得我們反覆推敲、仔細玩味。