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Week 6 · Lecture outline

Week 6 — Lecture Outline · Business Cycles & Short-Run Fluctuations

Principles of Macroeconomics · ECON 2 Fall 2026 · Prof. Ashford Fictional sample

Course: Principles of Macroeconomics (ECON 2) · Silver Oak University (fictional sample) · Prof. Ashford
Objective 5 — the AD–AS model & the business cycle; output gaps · SLO A & B
Meeting pattern: two 75-min sessions (≈150 min). Segment minutes below total ~150 — scale to your room.

The deck (E), the tutorial (C), and the workshop (P) all teach from this outline. Every number here is pre-computed and independently verified (see _build/logs/week-06-numbers.txt).

Week at a glance
Big question How do economists tell whether an economy is running above, at, or below its sustainable potential — and what does that gap imply?
By week's end students can (1) name and describe the phases of the business cycle (expansion, peak, recession, trough); (2) explain that potential output is a sustainable full-employment level, not a hard ceiling; (3) compute a recessionary gap and an inflationary gap (absolute size and %) from actual vs. potential output; (4) place a gap on the AD–AS diagram and describe what it implies for P and Y relative to potential; (5) describe how the NBER actually dates recessions and correctly frame "two negative quarters" as an informal rule of thumb, not the official definition; (6) present the classical self-correction view and the Keynesian sticky-wage/activist view evenhandedly.
Key vocabulary business cycle, expansion, peak, recession, trough, potential output (Y*), recessionary gap, inflationary gap, output gap, cyclical unemployment, Okun's law (rule of thumb), NBER, expectations, self-correction, sticky wages/prices, stabilization policy
Materials whiteboard; the Week-6 readings/links; Desmos or a spreadsheet (optional, for the AD–AS picture); an approved chatbot
Timing note 8 segments ≈ 150 min across two sessions. Trim Segment 7 (interaction) if short on time.

Segment 1 — HOOK: "The economy grew — is that good news or bad news?" (10 min)

Open with a mini-scenario: "Suppose next quarter's GDP report says real output rose. Everyone in this room should be relieved — right?" Let responses land, then complicate it: "It depends entirely on where output STARTED relative to potential. If the economy was below its sustainable capacity, growth back toward potential is straightforwardly good news. If the economy was already running ABOVE potential — overheating — more growth can mean rising inflation pressure, not relief." Land the reframe: you cannot evaluate a change in output without a benchmark, and that benchmark is potential output. Today's whole lecture builds the tool for making that comparison precisely.

Segment 2 — PLAIN-LANGUAGE IDEA: the business cycle & potential output (18 min)

Teach it in one sentence first, then formalize:

The business cycle is the recurring, irregular rise and fall of real GDP around its long-run growth path — and potential output is the sustainable level the economy tends toward when resources (especially labor) are fully employed, NOT the maximum it could ever produce.

The four phases (draw a wavy line around a rising trend line on the board):
- Expansion — real output is rising; more hiring, more spending.
- Peak — the high point before a downturn begins.
- Recession — real output is falling (or has fallen and stayed below potential); hiring slows, unemployment rises.
- Trough — the low point before the next expansion begins.

Misconception to kill immediately: "Potential output" sounds like it should mean "the absolute most the economy could ever produce." It doesn't. Potential output is the level consistent with full employment of resources at their sustainable, normal rate of use — the economy's long-run cruising speed. An economy CAN temporarily produce MORE than potential (by running factories past normal capacity, workers doing lots of overtime, unemployment falling below its natural rate) — that's not a superpower, it's unsustainable and inflationary, which is exactly why it's called a gap rather than an achievement.

Memory hook: "Potential output is cruising speed, not the speedometer's redline." You can run hotter than cruising speed for a while — it costs you in rising prices, not in impossibility.

Segment 3 — WORKED EXAMPLE #1: computing the recessionary and inflationary gaps (22 min)

Set it up on the board and do every step out loud — this is the week's anchor scenario.

Setup: an economy has potential output Y* = 1,000 (billions of dollars of real GDP, index units — keep it abstract and clean).

Case A — the economy runs below potential. Actual output Y = 950.
- Gap = potential − actual = 1,000 − 950 = 50.
- As a percentage of potential: 50 ÷ 1,000 × 100 = 5%.
- Since actual output is BELOW potential, this is a recessionary gap of 50 (5% of potential). Say it in words: the economy is producing 5% less than it sustainably could — resources (workers, factories) are sitting at least partly idle. This is NOT the same claim as "unattainable" — the resources to close this gap already exist; they're underused.

Case B — the economy runs above potential. Actual output Y = 1,040.
- Gap = actual − potential = 1,040 − 1,000 = 40.
- As a percentage of potential: 40 ÷ 1,000 × 100 = 4%.
- Since actual output is ABOVE potential, this is an inflationary gap of 40 (4% of potential). Say it in words: the economy is running hotter than its sustainable capacity — this typically shows up as rising inflation pressure, not as a free lunch.

✅ VERIFIED NUMBERS (pre-computed; do not recompute live)

Potential Y* = 1,000. Y = 950 → recessionary gap of 50 = 5% of potential. Y = 1,040 → inflationary gap of 40 = 4% of potential. (Python-checked; see _build/logs/week-06-numbers.txt.)

The rule students must internalize: subtract in the direction that keeps the sign meaningful — potential minus actual for a recessionary gap (a shortfall), actual minus potential for an inflationary gap (an overshoot) — then always express the size both in absolute units and as a percentage of potential, because "50" means nothing without knowing 50 out of how much.

Segment 4 — THE MODEL: gaps on the AD–AS diagram (25 min)

Bring back last week's AD–AS model (axes: real output Y on the horizontal axis, the price level P on the vertical axis; the aggregate-demand curve AD slopes down; short-run aggregate supply SRAS slopes up; long-run aggregate supply LRAS is a vertical line at potential output Y*).

Described-graph walkthrough — draw it as you go:

  1. Draw LRAS as a vertical line at Y* = 1,000. This line does not move with the price level — it marks the economy's sustainable full-employment output regardless of P.
  2. A recessionary gap: draw AD and SRAS crossing at a Y to the LEFT of the LRAS line (say, at Y = 950). Read it off: actual output (950) sits to the left of potential (1,000) — a recessionary gap of 50. The economy's short-run equilibrium is below its sustainable level; unemployment tends to run above its natural rate.
  3. An inflationary gap: draw AD and SRAS crossing at a Y to the RIGHT of the LRAS line (say, at Y = 1,040). Read it off: actual output (1,040) sits to the right of potential (1,000) — an inflationary gap of 40. The short-run equilibrium is ABOVE the economy's sustainable level; this shows up as rising price pressure, and unemployment tends to run below its natural rate (an unsustainable pace).
  4. Naming convention, said out loud: "recessionary gap" and "inflationary gap" describe the GAP's direction and typical consequence, not a claim that the economy must currently be in an official NBER recession or spiraling inflation — a small inflationary gap just means output is a bit above sustainable capacity.

✅ GRAPH-LOGIC CANON (verify every claim against this)

LRAS is vertical at potential output Y*; it does not shift with the price level. A recessionary gap = actual Y left of Y* on the diagram (below potential). An inflationary gap = actual Y right of Y* (above potential). Neither gap, by itself, tells you WHICH curve moved to put the economy there — that's a separate question (a demand-side shock moves AD; a supply-side shock moves SRAS) — the gap is a description of WHERE the economy currently sits relative to potential, read straight off the diagram.

The role of expectations (qualitative, one beat): if firms and workers expect a gap to persist, those expectations can get built into wage and price contracts — expected inflation, for instance, shifts SRAS (as you saw in Week 5's canon) — which is part of why gaps don't always close quickly or smoothly on their own. This sets up Segment 5's evenhanded debate.

Segment 5 — NBER DATING + NAMED MISCONCEPTION: "two negative quarters" (18 min)

Factual framing, no editorializing: in the United States, the official arbiter of recession dates is the Business Cycle Dating Committee of the National Bureau of Economic Research (NBER) — a nonpartisan group of academic economists. Point to the week's DATA link (NBER's own Business Cycle Dating page) and describe their actual method: the committee looks at several indicators together — real income, employment, industrial production, and real sales, alongside GDP — and identifies peak and trough months, not quarters, using judgment rather than a single mechanical formula. They do not require, and do not use, a fixed rule like "two consecutive quarters of negative real GDP growth."

Name the misconception directly: "Two consecutive quarters of negative real GDP growth" is a widely repeated informal rule of thumb — a quick, popular shorthand that gets close to the right answer much of the time, especially for garden-variety downturns. It is genuinely useful as a mental estimate. But it is not the NBER's official definition, and the two can diverge: a downturn with only one very sharp negative quarter, or a downturn visible clearly in employment and income data without two full negative GDP quarters, can still be dated a recession by the committee. Teach both facts side by side — the rule of thumb is useful AND it is not the official rule — this is a factual distinction, not a matter of opinion.

Cure the trap on the board: write "Rule of thumb: 2 negative quarters (popular, approximate)" next to "Official: NBER committee judgment across multiple indicators (peak/trough dating)" and underline that both statements can be true at once without contradiction.

Segment 6 — TECHNOLOGY WORKFLOW + AI-CRITIQUE (18 min)

Live demo (optional Desmos/spreadsheet): if useful, sketch the vertical LRAS line at Y = 1,000 alongside an AD–AS crossing at 950 (recessionary) and one at 1,040 (inflationary) to reinforce "left of potential" vs. "right of potential."

AI-critique moment (do this with the class): Ask an approved chatbot: "An economy has potential output of 1,000 and actual output of 950. Is this a recessionary or inflationary gap, what is its size, and what percentage of potential is that? Also, is 'two consecutive quarters of negative GDP growth' the official U.S. definition of a recession?" Then audit it together: the correct answers are recessionary gap, size 50, 5% of potential, and NO — the official definition is the NBER committee's multi-indicator dating; "two negative quarters" is only an informal rule of thumb. Chatbots frequently flip the gap direction or the subtraction order (computing 950 − 1,000 and reporting a negative number without correctly naming it a shortfall), misstate the percentage (dividing by the wrong base), or confidently assert that "two negative quarters" IS the official U.S. definition — this is one of the most common macro factoids chatbots get wrong with total confidence. Make the class catch each error and state the correct reasoning. The habit all term: the tool drafts, you judge.

Segment 7 — INTERACTION: mini-debate (self-correction vs. activism) (19 min)

Pose the debate students will develop further in Discussion 6: "Suppose the economy has a recessionary gap. Left alone, will it close on its own — and if so, how fast?"

Split the room (or pairs) into two positions and have each argue its strongest case:

  • The classical/self-correction case: given enough time, wages and prices are flexible — a recessionary gap means unemployment is above its natural rate, which puts downward pressure on wages; falling wages lower production costs, shifting SRAS to the right until the economy returns to potential on its own. Government intervention is unnecessary and risks making things worse (timing, unintended distortions).
  • The Keynesian/sticky-wage case: in the short run, wages and prices are "sticky" — they adjust slowly (long contracts, social norms against nominal wage cuts, menu costs) — so the self-correction mechanism can take a long time, and a lot of real hardship (prolonged unemployment) can accumulate while waiting. Active fiscal or monetary stabilization can close the gap faster than the economy would on its own.

Debrief: both sides agree the LONG RUN destination is potential output; they disagree about how long the short run lasts and whether the wait is worth avoiding. This is the Week-15 debate previewed early — do not resolve it today; flag that Discussion 6 is exactly this question.

Segment 8 — CALLBACKS, TEASE & THE WEEK'S WORK (10 min)

  • Callback: every example today shared one engine — "gap" is a measured DISTANCE between actual output and potential output, and its direction (left or right of the vertical LRAS line) tells you whether the economy is running cold or hot relative to its own sustainable capacity.
  • Tease next week: "If a recessionary gap might take a long time to close on its own, does the government have a tool to speed it up? Next week: fiscal policy — how government spending and taxes move AD, and the multiplier that makes a dollar of spending do more than a dollar of work."
  • The week's work: Lecture Tutorial (business cycle → potential output → gaps → NBER dating → self-correction vs. activism), Practice (6 reps), Quiz 6, Discussion 6, Assignment 6, and Workshop 6 — "Diagnose the Gap."

Instructor FAQ — common stumbles

  • "Isn't potential output the most the economy CAN produce?" No — it's the sustainable, full-employment level. The economy can run above it for a while (an inflationary gap), just not indefinitely without rising inflation pressure.
  • "If actual output is below potential, is that automatically 'a recession'?" Not automatically in the OFFICIAL sense — a recessionary gap is a graphical/measurement fact (Y < Y*); an official NBER recession is a specific, committee-dated episode. A small, brief recessionary gap need not be dated a recession by the NBER; a genuine recession will typically show up as a (often sizable, often sustained) recessionary gap, but the two concepts are not identical.
  • "Is 'two negative quarters' wrong, then?" It's not "wrong" as a rule of thumb — it's a reasonably useful quick estimate — it's wrong only if presented as the official U.S. definition, which it is not. Teach the distinction, not a verdict on the rule of thumb's usefulness.
  • "Which way do I subtract for each gap?" Recessionary (below potential): potential − actual (a positive shortfall). Inflationary (above potential): actual − potential (a positive overshoot). Never leave a negative number unlabeled — name which gap it is in words.
  • "Does Okun's law tell us exactly how much unemployment a gap implies?" No — it's a rule of thumb (roughly 2% of output per point of cyclical unemployment), useful for a quick, order-of-magnitude estimate, never a precise law. Label it that way every time it comes up.
  • "Who's right, the classical or the Keynesian view?" Present both at full strength; do not declare a winner. The agreed ground: in the long run, both traditions expect the economy to return to potential — the genuine disagreement is about how long that takes and whether active policy should speed it up.

~ Prof. Ashford's edition · Fall 2026 · built with thecoursemaker.com