On the Influence of Demand and Supply on Prices

Price movements can look alike while coming from very different causes. Ricardo separates a temporary market price, produced by today's demand and supply, from the natural price, the cost-based level around which reproducible goods tend to settle.

Term	Meaning
Market price	The price actually paid now, which can move with a shortage, glut, or sudden change in demand
Natural price	The price that covers the ordinary cost of reproducing a commodity, including ordinary profit
Cost of production	The labour, materials, capital advances, and ordinary return required to reproduce a good
Reproducible commodity	A good whose quantity can be expanded to a moderate degree when production becomes attractive
Monopoly	A case where supply cannot freely expand because control or scarcity blocks competition
Money value	A price stated in money; it can change because money itself changes value

The immediate and lasting questions need different clocks; otherwise a temporary shortage is mistaken for a permanent law. Ricardo grants demand and supply control over today's market price, but argues that production cost regulates the lasting price of goods that competitors can reproduce.

Clock	Main question	Regulating force
Short run	Why is the price unusual today?	Current demand relative to current supply
Adjustment	What does the unusual profit induce?	Capital enters profitable trades or leaves losing trades
Long run	Where can the price persist?	The cost of reproducing the commodity

Ricardo's claim is a tendency, not a promise that adjustment is instant. Skills, machines, leases, information, and legal restrictions can slow or block the movement of capital.

TODAY                         AFTER ADJUSTMENT
demand > available supply
          |
          v
market price above cost  ---> entry ---> more supply
                                      ---> price gap narrows

A sudden fashion change can raise the price of hats without raising their production cost. The miniature makes the temporary profit signal visible before producers have time to respond.

Suppose the natural price of a hat is 100. Demand rises from 100 hats to 130, while only 100 hats are immediately available.

Moment	Demand	Supply	Illustrative market price	What producers see
Before fashion changes	100	100	100	Ordinary profit
Immediately after	130	100	130	Extra profit
After entry expands supply	130	125	105	A much smaller extra profit
After full adjustment	130	130	100	Ordinary profit again

The price figures are a teaching index, not numbers quoted by Ricardo. The important sequence is his: higher demand first lifts market price; unusual profit attracts capital; added supply then pushes price back toward production cost.

The adjustment is manipulable because demand, supply, cost, and capital mobility play distinct roles. The existing Lab lets each move separately, which is exactly the distinction Ricardo wants the reader to test.

Start with natural price at 100, demand at 125, supply at 95, and capital mobility at 5. First raise demand and watch the market-price gap widen. Then raise capital mobility and watch the adjusted price move closer to natural price. Finally lower natural price while holding demand and supply fixed; this represents a production-cost improvement rather than a fall in demand.

This is a conceptual reconstruction, not Ricardo's formula or a calibrated supply-and-demand model. It preserves his separation between a temporary imbalance, a cost-based centre, and capital-driven adjustment. It assumes a linear price gap, scalable production, one representative trade, and no adjustment delay. It would fail as an adaptation if raising capital mobility pushed the adjusted price farther from natural price, or if changing only natural price were described as a demand change.

A fall in production cost can lower price even when demand and supply change little. Ricardo uses improved agriculture to show why a supply-demand ratio alone cannot explain every lasting price movement.

Assume an agricultural discovery cuts the natural price of bread in half. People may not eat twice as much bread merely because it is cheaper, and bakers will not produce unwanted loaves. Quantity demanded and quantity supplied may therefore remain nearly equal at a similar level while the lasting money price falls by 50 percent.

before discovery                 after discovery
cost per loaf: 100               cost per loaf: 50
quantity bought: 1 loaf          quantity bought: about 1 loaf
demand = supply                  demand = supply

price falls because reproduction became cheaper,
not because demand fell below supply.

This is Ricardo's strongest counterexample to the slogan that price varies only with the demand-to-supply ratio.

A higher number on a price tag does not prove that buyers want a larger quantity. If money loses value, the same goods may command 10 or 20 percent more money while the quantity bought remains unchanged.

Ricardo is policing language here. Demand increases only when an additional quantity is purchased or consumed. More currency units spent on the same quantity can instead reflect a change in the measuring unit.

Observation	Possible cause	What would distinguish it?
Hat price rises; more hats are bought	Increased demand	Physical quantity purchased rises
Every money price rises; quantities are stable	Money loses value	The change is broad across commodities
Bread price falls; quantities barely move	Production becomes cheaper	Unit cost falls while demand and supply remain balanced

Ricardo's cost-centre argument weakens when competitors cannot expand supply. For monopolized goods, restricted quantity and buyers' eagerness can regulate price for much longer because entry cannot produce the ordinary competitive correction.

The boundary matters for rare art, exclusive privileges, and naturally fixed supplies. Ricardo is not claiming cost regulates every price regardless of institutions; he explicitly limits the long-run rule to commodities open to reproducible competition.

The primary chapter contains prose and verbal examples but no source figure, chart, or table. The diagrams, miniature, and Lab therefore organize Ricardo's argument without claiming to transcribe an original visual.

Source item	Printed pages	Type	Course treatment	Fidelity
Hats: doubled demand and temporary price rise	542–548	Verbal mechanism	Two-clock diagram, miniature, and Lab protocol	Conceptual reconstruction
Bread: 50 percent production-cost fall	547–548	Verbal counterexample	Before/after margin diagram	Conceptual reconstruction
Money loses value while quantity bought is unchanged	543–544	Verbal counterexample	Causal diagram and comparison table	Conceptual reconstruction
Monopoly versus reproducible competition	548	Verbal boundary case	Decision diagram	Conceptual reconstruction

The reconstructions preserve the direction of Ricardo's claims. They do not provide empirical demand curves, measured adjustment speeds, modern theories of expectations, strategic pricing, inventories, market power, or costs that change with output.

Ricardo's target is not demand and supply themselves, but the mistake of using them as a complete explanation for every price. The right explanation depends on the time horizon, the production cost, the value of money, and whether supply can expand.

• Demand and supply can move the market price immediately.
• Unusual profit or loss redirects capital and changes future supply.
• For reproducible competitive goods, production cost regulates the price that can persist.
• A cost reduction can lower price even when demand and supply remain balanced.
• A fall in money's value can raise money prices without increasing physical demand.
• Monopoly and fixed scarcity limit the competitive adjustment on which Ricardo relies.
• The Lab is a conceptual reconstruction of these distinctions, not a calibrated modern market model.

The chapter is mastered when you can diagnose a price change before naming its cause.

• [ ] Can you distinguish market price from natural price?
• [ ] Can you explain why a demand shock creates only a temporary price gap in Ricardo's competitive case?
• [ ] Can you follow the hat miniature from shortage to entry to expanded supply?
• [ ] Can you use the Lab to change demand without changing production cost?
• [ ] Can you use the Lab to make capital mobility narrow the adjusted price gap?
• [ ] Can you explain why cheaper bread can fall in price without a demand collapse?
• [ ] Can you distinguish a rise in money prices from an increase in physical demand?
• [ ] Can you name the monopoly boundary to Ricardo's cost-of-production rule?
• [ ] Can you state what the conceptual reconstruction leaves out?