Real prices and ideal prices

Real prices and ideal prices refers to a distinction between actual prices paid for products, services, assets and labour (the money that actually changes hands), and computed prices which are not actually charged or paid in market trade, although they may facilitate trade. The difference is between actual prices paid, and information about possible, potential or likely prices, or "average" price levels. This distinction should not be confused with the difference between "nominal prices" (current-value) and "real prices" (adjusted for price inflation, and/or tax and/or ancillary charges).

Ideal prices, expressed in money-units, can be "estimated", "theorized" or "imputed" for accounting, trading, marketing or calculation purposes, for example using the law of averages. Even if such prices therefore may not directly correspond to transactions involving actually traded products, assets or services, they can nevertheless provide "price signals" which influence economic behavior. For example, if statisticians publish aggregated price estimates about the economy as a whole, market actors are likely to respond to this price information, even if it is far from exact, based on a very large number of assumptions, and later revised. The release of new GDP data, for instance, often has an immediate effect on activity, insofar as it is interpreted as an indicator of whether and how fast the market – and consequently the incomes generated by it – is growing or declining.

Ideal prices are typically prices that would apply in trade, if certain assumed conditions apply (and they may not).

The distinction is currently best known in the profession of auditing. It also has enormous significance for economic theory, and more specifically for econometric measurement and price theory; the main reason is that price data is very often the basis for making economic and policy decisions.

A distinction between real (or actual) prices and ideal prices, was introduced in Marx's Grundrisse notebooks. In A Contribution to the Critique of Political Economy (1859), Marx already criticizes James Steuart and John Gray because they fudged the distinction between actual prices and ideal prices. In chapter 3 of the first volume of Das Kapital, Marx states:

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