The pioneer in distinguishing the different types of price levels from one another was Edgeworth. The first thorough classification of index numbers of prices was that prepared by him in his memoranda for the British Association (1887 to 1889), which still remain the most important discussions of this matter. He there distinguishes six leading types—the capital standard, the consumption standard, the currency standard, the income standard, the indefinite standard and the production standard. Nearly forty years later (Economic Journal, vol. xxxv (1925), p. 379) Edgeworth classified index numbers into three leading types—index numbers representing welfare, unweighted index numbers and the labour standard. Of these three categories the first and third correspond to variants of the consumption and earnings standards as defined above; and the second, in respect of which I have a fundamental difference of opinion with Edgeworth, will be dealt with in the second section of chapter 6.

But in addition to these fundamental price levels, we have a plurality of secondary price levels corresponding, not to the general purchasing power of money over consumption as a whole or over effort as a whole, but to its purchasing power for special purposes; as, for example, the purchasing power of money over staple commodities at wholesale, or over bonds and shares, and so forth. Further, in addition to these partial but more or less generalised price levels, there are also a number of subsidiary price levels, useful for particular purposes or as component parts in building up the more generalised price levels.