Marginal Utility, Value Theory, and Demand-Supply Foundations

Labor Theory of Value vs Marginal Utility

Labor theory of value: value = total inputs/costs; viewed as invariant. Fails to predict prices well.
Marginal revolution: value is subjective and depends on marginal utility; key contributors: Carl Menger, William S. Jevons, and Léon Walras.
Diamond–water paradox resolved by marginal utility: value comes from the usefulness of the last unit (marginal usefulness).
Higher-order vs lower-order goods: inputs (higher-order) used to produce finished goods (lower-order); input value derives from ability to produce the final good; leads to derived demand.
Marxists retain labor theory of value; modern market economics emphasizes subjective value and the role of buyers and sellers.
Example intuition: identical goods can have different values due to preferences (e.g., a Dallas Cowboys vs. NY Giants shirt).

As you consume more of a good, each additional unit provides less extra usefulness (diminishing marginal utility).
Time/place/circumstances alter value: e.g., a water bottle is worth more when you’re dehydrated in the desert than when you’re at a fountain.
Value is subjective and revealed through market transactions; both buyers and sellers matter.
The “magical goose of capitalism” idea: labor power is a special input whose use-value (creating new value) may exceed the wage paid.

Demand vs. supply: buyer behavior driven by marginal value; seller behavior driven by marginal cost.
Demand curve interpretation: a marginal value curve; at price $P$, the quantity demanded $Q$ is where MV of the last unit equals $P$.
If price falls, more buyers/trades occur; if price rises, fewer trades occur.
The equilibrium condition (simplified):
- MV = MC at the market-clearing quantity, in competitive markets.
Gains from trade and economic welfare:
- Total gains from trade (W) = sum of individual trades of (MV − MC) across all units traded.
- Economic welfare = percent of potential gains from trade captured by transactions:
  W = \frac{\text{Gains from trade captured}}{\text{Total potential gains from trade}} \times 100\%.
- Efficient market (perfect competition) = 100% of potential gains captured; real markets are usually less than 100%.
Consumer surplus (brief): area under the demand curve and above the price represents extra value to buyers.

Law of demand:, ceteris paribus, price ↑ leads to quantity demanded ↓; price ↓ leads to quantity demanded ↑.
Demand curve is a marginal value curve: at each quantity, the price = marginal value of the last unit.
Shifts vs movements:
- Movement along the curve = change in quantity demanded due to a price change.
- Shift of the curve = change in demand due to non-price factors (income, tastes, etc.).

Income level shifts demand: higher income generally increases demand.
Prices of related goods in consumption: substitutes and complements affect demand.
Number of buyers, tastes, and expectations about future prices.

Changes in input prices (costs) shift supply; higher input prices reduce supply.
Technology and productivity: improvements lower costs and increase supply.
Taxes and subsidies: affect production costs and incentives to supply.
Expectations about future prices; entry and exit of producers.
Prices of goods related in production (complements/substitutes in production) can shift supply.
Opportunity costs: choosing between alternative uses of resources affects supply decisions.

Law of supply: price and quantity supplied move together (positive relationship).
Supply curve reflects marginal cost (MC): higher price justifies supplying more because it covers higher marginal costs.
Shift factors for supply are non-price factors that move the entire supply curve.

Market transactions occur when MV > MC for some units; trades stop when MV ≤ MC.
Price allocation splits the gains from trade between buyers and sellers but does not affect the total gains.
Equilibrium in a competitive market maximizes the captured gains from trade; other market structures are often inefficient relative to this benchmark.

Derived demand: demand for inputs (e.g., labor) arises from the demand for the final goods those inputs help produce.
Labor power as a commodity: wage is the price of labor, but use-value of labor power is in its ability to create new value.
Real-world intuition: profits depend on more than wages (capital, equipment, premises, energy, and organization all contribute).
If workers create more value than their wages, the surplus accrues to capital owners, giving rise to profit.

Value is not fixed by producers alone; it is subjective and context-dependent.
The marginal unit’s value drives willingness to pay and helps explain price formation.
Demand and supply curves are marginal-value and marginal-cost concepts, respectively, and shifts are driven by non-price factors.
Economic welfare measures how much of the total possible gains from trade are actually realized through transactions.
Derived demand links the demand for factors of production to the demand for final goods.
The market is a complex, interconnected system where price signals coordinate buyers, sellers, and resources across the economy.