Classical Trade: Absolute Advantage and Comparative Advantage

Mercantilism and the Classical Model

Mercantilists (pre-1776) viewed international trade as a zero-sum game where wealth defined a country’s well-being.
- Trade surplus → wealth inflow (gold/silver) for the surplus country.
- Trade deficit → wealth loss for the deficit country.
Adam Smith’s critique: wealth is not consumption; wealth is a proxy for the potential to consume in the future. Consumption is what makes a country actually well off.
The classical model introduces two main trade theories:
- Absolute advantage
- Comparative advantage

Core idea behind absolute advantage

Absolute advantage sets the idea that a country should specialize in the good for which it requires less labor to produce (i.e., has an absolute efficiency edge) and trade for the other good.
Key intuition: different autarkic prices across countries arise from differences in production technology/productivity, which creates price differences when trade is allowed.
In the model, we assume differences in technology/productivity drive price differences, which creates a basis for trade.

Basic assumptions of the classical model (brief recap)

Resources are immobile across countries (country-specific).
No trade barriers (no tariffs, quotas).
Exports must pay for imports; labor is the only relevant input (labor theory of value).
Perfect competition and full employment.
Production exhibits constant returns to scale: if you double the inputs, you double output.

The production data you’ll use (Country A vs Country B)

Labor requirements (units of labor per unit produced):
- For good S:
- Country A: $L_S^A = 3$
- Country B: $L_S^B = 12$
- For good T:
- Country A: $L_T^A = 6$
- Country B: $L_T^B = 4$
Summary: Country A is more productive in S; Country B is more productive in T.
Note on arithmetic in the transcript: some steps mix up the exact changes when shifting labor between sectors. The corrected, consistent results are used below (see explicit costs and comparative advantages).

Absolute advantage in the example

Determine who has absolute advantage in each good by comparing labor requirements:
- Good S: A uses 3 labor vs B uses 12 labor → A has an absolute advantage in S.
- Good T: B uses 4 labor vs A uses 6 labor → B has an absolute advantage in T.
Implication: Under absolute advantage, country A should specialize in S and country B should specialize in T, then trade for the other good.
How does trade help? If both countries shift toward their absolute advantages, world output increases without more resources.
- Example logic (using the production data above):
- If A reduces tea production by 1 unit (from T), saving 6 labor, they can instead produce 2 extra units of S (since S costs 3 labor per unit).
- If B reduces S production by 1 unit (freeing 12 labor), they can produce 3 extra units of T (since T costs 4 labor per unit).
- Net effect: World production increases by ig( ext{S increases by } 2ig) + ig( ext{S decreases by }1ig) = +1 unit of S and
  ig( ext{T increases by }3ig) + ig( ext{T decreases by }1ig) = +2 units of T.
- This demonstrates mutual gains from trade under absolute advantage (assuming all resources are already fully employed).

Why the market would realize these gains (price mechanism under autarky and trade)

Autarky price relationships (costs in terms of the other good):
- Price of S in terms of T (i.e., how many units of T per 1 unit of S) in autarky:
- In Country A: $p{S|T}^A = rac{LS^A}{L_T^A} = rac{3}{6} = rac{1}{2}$ $ext{T per } S$
- In Country B: $p{S|T}^B = rac{LS^B}{L_T^B} = rac{12}{4} = 3$ $ext{T per } S$
- Price of T in terms of S (reciprocal):
- In Country A: $p{T|S}^A = rac{LT^A}{L_S^A} = rac{6}{3} = 2$ $ext{S per } T$
- In Country B: $p{T|S}^B = rac{LT^B}{L_S^B} = rac{4}{12} = rac{1}{3}$ $ext{S per } T$
These autarky prices imply the following: S is cheaper in Country A (lower price in terms of T), and T is cheaper in Country B (lower price in terms of S).
With trade, relative prices converge to a common range (the terms of trade) that lies between the two autarky prices, enabling mutually beneficial exchanges.

Autarky vs trade: intuition for the market process

If trade is allowed, demand shifts and resources reallocate toward the good where each country has a comparative advantage, driving the terms of trade toward an equilibrium between the two autarky price ratios.
Under absolute advantage, the fundamental question is: will the two countries’ price signals align to reallocate resources toward the country-specific advantages? The answer is yes in the basic model: prices incentivize specialization and trade.

Absolute advantage: limitations (why Ricardo later refined the model)

Absolute advantage cannot explain trade between countries with similar technologies/productivities; price differences may be small or absent.
If one country has an absolute advantage in both goods, the absolute-advantage model would predict no mutual benefit from trade (which is not always realistic).
This motivates the move to comparative advantage, which depends on relative (not absolute) productivity differences.
In short: absolute advantage explains some gains, but comparative advantage explains a broader set of real-world trade patterns.

Comparative advantage (David Ricardo) – main idea

Comparative advantage looks at relative efficiency, i.e., opportunity costs, rather than absolute production costs.
A country has a comparative advantage in producing a good if its opportunity cost of producing that good is lower than in the other country.
Even when one country is more productive in producing both goods (absolute advantages in both), trade can be mutually beneficial if each country specializes in the good in which it has the lower opportunity cost.

Continued example: calculating opportunity costs for S and T

Given the same data:
- Country A:
- To produce 1 unit of S costs 3 labor; to produce 1 unit of T costs 6 labor.
- Country B:
- To produce 1 unit of S costs 12 labor; to produce 1 unit of T costs 4 labor.
Opportunity costs (pre-trade, autarky):
- In Country A:
- Opportunity cost of 1 unit of S in terms of T: $OCS^A = rac{LS^A}{L_T^A} = rac{3}{6} = rac{1}{2} ext{ T}$
- Opportunity cost of 1 unit of T in terms of S: $OCT^A = rac{LT^A}{L_S^A} = rac{6}{3} = 2 ext{ S}$
- In Country B:
- Opportunity cost of 1 unit of S in terms of T: $OCS^B = rac{LS^B}{L_T^B} = rac{12}{4} = 3 ext{ T}$
- Opportunity cost of 1 unit of T in terms of S: $OCT^B = rac{LT^B}{L_S^B} = rac{4}{12} = rac{1}{3} ext{ S}$
Interpretation: Although Country A has an absolute advantage in both goods, the comparative advantage framework says:
- Country A has a comparative advantage in S (lower OC of S in terms of T: OCS^A = frac{1}{2} ext{ T} < OCS^B = 3 ext{ T}).
- Country B has a comparative advantage in T (lower OC of T in terms of S: OCT^B = frac{1}{3} ext{ S} < OCT^A = 2 ext{ S}).
Therefore, the predicted trade pattern under comparative advantage is: A should specialize in S, B should specialize in T, and trade for the other good.

Relative costs and the comparative advantage results (summary)

In autarky, price ratios reflect opportunity costs and technology:
- Price of S in terms of T:
- In A: $p{S|T}^A = rac{LS^A}{L_T^A} = rac{3}{6} = rac{1}{2} ext{ T per } S$
- In B: $p{S|T}^B = rac{LS^B}{L_T^B} = rac{12}{4} = 3 ext{ T per } S$
- Price of T in terms of S:
- In A: $p{T|S}^A = rac{LT^A}{L_S^A} = rac{6}{3} = 2 ext{ S per } T$
- In B: $p{T|S}^B = rac{LT^B}{L_S^B} = rac{4}{12} = rac{1}{3} ext{ S per } T$
Comparative advantage implies:
- A has comparative advantage in S (lower OC of S).
- B has comparative advantage in T (lower OC of T).
Therefore, trade should be: A exports S to B; B exports T to A.
This result holds even if A has an absolute advantage in both goods, which is the key improvement of Ricardo’s theory: focus on relative (not just absolute) productivity.

What happens if both countries produce both goods (resource reallocation within each country)

It is still possible to reallocate resources within countries to increase world output when both countries have some comparative advantages.
- Country A should move resources toward S; Country B toward T, even without changing which country produces which good.
- The same logic of opportunity costs applies: reallocation increases total production and thus consumption possibilities through trade.
A stylized illustration uses the idea of refactoring a country’s production possibilities curve (PPC) and then showing how trade expands consumption possibilities while keeping production capabilities determined by technology and resources.

Production possibilities and trade geometry (illustrative numbers)

Suppose country A has 12{,}000 units of labor and country B has 9{,}600 units.
- PPC for Country A (given the data: S uses 3 labor; T uses 6 labor):
- All S: 12{,}000 / 3 = 4{,}000 units of S, 0 T.
- All T: 12{,}000 / 6 = 2{,}000 units of T, 0 S.
- So PPC_A has endpoints (S,T) = (4{,}000, 0) and (0, 2{,}000).
- PPC for Country B:
- All S: 9{,}600 / 12 = 800 units of S, 0 T.
- All T: 9{,}600 / 4 = 2{,}400 units of T, 0 S. (Note: the transcript gave 1{,}200; correct calculation is 2{,}400.)
In autarky, each country’s consumption possibilities coincide with its PPC (production equals consumption).
With trade under comparative advantage, each country specializes in its comparative advantage good and consumes beyond its own PPC due to terms of trade.

The terms of trade and the trade triangle (intuitive and graphical ideas)

The terms of trade is the rate at which goods are exchanged between countries; it lies between the two autarky price ratios.
- In this example, a plausible range for the terms of trade is between the autarky prices for S in each country:
- Lower bound: $p_{S|T}^{A} = frac{1}{2} ext{ T per } S$
- Upper bound: $p_{S|T}^{B} = 3 ext{ T per } S$
An example equilibrium terms of trade (illustrative) could be $p^{eq} = rac{3}{4} ext{ T per } S$ (i.e., S is traded for some number of T in between the two autarky ratios).
The price line (the terms of trade) in each country shows the slope of the new consumption possibilities curve after trade.
- In Country A, with trade, the price of S in terms of T being $p^{eq} = frac{3}{4}$ means they can trade 4 S for 3 T (or equivalently 1 S for 0.75 T).
- In Country B, the same terms of trade implies the reciprocal exchange rates in their terms of trade.
Exports and imports form a trade triangle in each country:
- Country A exports S and imports T (exports of S equal to imports of S by Country B, and imports of T equal to exports of T by Country B).
- The width of the triangle aligns with the amount traded and the slope with the terms of trade.
The key takeaway: with trade, consumption possibilities expand without altering the country’s production capabilities, thanks to the new allocation of outputs enabled by comparative advantages and price signals.

Consumption possibilities and the rotation of the budget frontier

Before trade (autarky): consumption possibilities coincide with production possibilities (PPC).
After trade: the consumption possibilities curve (CPC) expands and rotates outward, while the PPC (production capabilities) remains the same (determined by technology/resources).
The new CPC is tangent to a price line with slope equal to the terms of trade; this tangent point yields the country’s post-trade optimum consumption bundle.
In words: trade rotates the country’s budget line, expanding consumption possibilities, even though production routes and capabilities do not improve; the welfare (consumption) improves.

Summary takeaways

Absolute advantage shows that trade can be mutually beneficial when countries differ in productivity, but it cannot explain trade when productivity is similar or when one country is better at both goods.
Comparative advantage explains why trade can be beneficial even when one country has absolute advantage in both goods: trade is driven by relative (not absolute) productivity differences, i.e., relative opportunity costs.
Trade expands consumption possibilities (the CPC rotates outward) but does not expand production possibilities (the PPC remains), given fixed technology and resource endowments.
The optimal pattern: specialize in the good in which you have a comparative advantage and trade for the other good; this yields higher combined output and higher consumption possibilities for both countries.

Quick reference formulas (summary)

Labor requirements:
- $LS^A = 3, eq LS^B = 12,</li><li>$ LT^A = 6, eq LT^B = 4 $</li></ul></li><li>Autarky price of S in terms of T:<ul><li>Country A:$ p{S|T}^A = rac{LS^A}{L_T^A} = rac{3}{6} = rac{1}{2} ext{ T per } S $</li><li>Country B:$ p{S|T}^B = rac{LS^B}{L_T^B} = rac{12}{4} = 3 ext{ T per } S $</li></ul></li><li>Autarky price of T in terms of S:<ul><li>Country A:$ p{T|S}^A = rac{LT^A}{L_S^A} = rac{6}{3} = 2 ext{ S per } T $</li><li>Country B:$ p{T|S}^B = rac{LT^B}{L_S^B} = rac{4}{12} = rac{1}{3} ext{ S per } T $</li></ul></li><li>Opportunity costs (comparative advantage):<ul><li>OC of S in A:$ OCS^A = rac{LS^A}{L_T^A} = rac{1}{2} ext{ T} $</li><li>OC of S in B:$ OCS^B = rac{LS^B}{L_T^B} = 3 ext{ T} $</li><li>OC of T in A:$ OCT^A = rac{LT^A}{L_S^A} = 2 ext{ S} $</li><li>OC of T in B:$ OCT^B = rac{LT^B}{L_S^B} = rac{1}{3} ext{ S} $</li></ul></li><li>Suggested trade pattern (comparative advantage): A exports S; B exports T.</li><li>Gains from moving toward comparative advantage (within-country reallocations possible): reallocations can raise world output and consumption with the same resources.</li><li>Terms of trade (illustrative) with equilibrium between autarky prices:$ p^{eq} ext{ lies between } p{S|T}^A = frac{1}{2} ext{ and } p{S|T}^B = 3. $Example:$ p^{eq} = frac{3}{4} ext{ T per } S.$$