Definition
The labour theory of value (LTV) holds that the exchange value of a commodity is determined by the quantity of labour required to produce it. It is the classical economists’ answer to the question: what makes things valuable in exchange?
adam-smith articulates it in The Wealth of Nations (Book I, Ch. V):
“Labour…is the real measure of the exchangeable value of all commodities.”
His reasoning: labour is the one input that doesn’t change in its own value — equal quantities of labour always cost the worker the same toil and sacrifice. Gold, silver, and corn all fluctuate in value relative to one another; labour is the invariant standard.
The Water-Diamond Paradox
Smith notices but doesn’t fully resolve the apparent contradiction: water has enormous use value but almost no exchange value, while diamonds have almost no use value but enormous exchange value. If labour determines value, why aren’t things valued by their usefulness?
Smith distinguishes:
- Use value: utility, the satisfaction the thing provides
- Exchange value: the quantity of other goods it can command in trade
The paradox arises because he doesn’t have the concept of marginal utility. Water is abundant; the marginal unit of water (the next glass) is nearly free. Diamonds are scarce; every diamond is marginal. The resolution — that value is determined by marginal utility, not total utility — was supplied by Jevons, Menger, and Walras in the 1870s, a century after Smith.
Real vs. Nominal Price
Smith distinguishes two measures of price:
- Real price: the quantity of labour a commodity can command — the true measure of its value across time and places
- Nominal price: the money price — useful for comparing things at one time and place, but unreliable across centuries or countries because the value of money itself changes
For cross-temporal comparisons, Smith argues corn is a better standard than gold, because the labour required to produce a given quantity of corn stays more constant than the labour required to mine a given weight of gold.
Historical Development and Limitations
Ricardo and Marx
David Ricardo (1817) refined the labour theory: the ratio of exchange between two goods is determined by the ratio of labour hours required. This formulation is cleaner but runs into the problem of capital — machines are made of past labour, so how does capital’s contribution fit in?
Karl Marx (1867) made the LTV the foundation of his critique of capitalism: the difference between the labour value embodied in a commodity and the wages paid to workers is “surplus value,” appropriated by the capitalist. This is the source of profit in Marxist political economy.
The Marginalist Revolution
The LTV was largely displaced in mainstream economics by the marginalist revolution of the 1870s. Value is not determined by the total quantity of labour in production but by marginal utility to the buyer and marginal cost of supply. This explains the water-diamond paradox and allows a unified theory of value.
What the LTV Gets Right
Despite its limitations, the LTV captures something real: cost of production (including labour) sets a floor on long-run price. Commodities cannot trade indefinitely below their cost of production — suppliers will exit. The LTV is approximately correct for competitive, homogeneous goods produced with similar capital intensity.
Connections
natural-vs-market-price
Smith’s natural price — the long-run equilibrium price — is grounded in the labour theory of value. It is the price that covers labour costs (wages), return on capital (profit), and land cost (rent) at ordinary rates.
prospect-theory (negative connection)
The LTV assumes economic actors have stable, objective preferences. Kahneman’s prospect theory demonstrates that value is inherently subjective, reference-dependent, and context-sensitive — the exact opposite of an objective labour-determined value.
compound-interest
Munger’s insight that compound interest applies to knowledge and relationships, not just money, is loosely analogous to the LTV extended beyond physical labour: accumulated understanding has value that can be compounded.