Key Idea: The demand and supply curves assume people always choose well: they know every option, weigh it up, and pick the best. Real people buy on impulse, follow habits, and take the default. This topic is about where that assumption breaks, for consumers and for firms, and what a government can do with that knowledge. Where you meet it:
Paper 1
- Essays.
- Discuss [15]: do consumers really maximise utility? Do firms really maximise profit?
Paper 3
- Policy paper.
- Define [2]: rational consumer choice, bounded self-control, a nudge.
- Explain [4] a limitation, then Recommend [10] a policy, often a nudge.
Every evaluation
- The counter-argument.
- Should the government tax it? A nudge may do the job without changing any price.
The model, and where it breaks
The rational consumer maximises utility, meaning satisfaction. The rational firm maximises profit. Both are assumed to have full information and to weigh every option. The model is useful because it predicts the demand and supply curves. It is not true, in four named ways.
| The model assumes | Where it breaks | What it looks like |
|---|---|---|
| you can process every option | bounded rationality | you cannot compare every phone plan, so you pick one that is good enough: satisficing |
| you do what you know is best | bounded self-control | you know the better choice and still do not make it: the gym you pay for and skip |
| you care only about yourself | bounded selfishness | tipping, giving to charity, paying more for fair trade |
| you know every price and option | imperfect information | buying the first insurance quote because comparing them all takes too long |
The model is kept because it predicts well on average: demand slopes down, supply slopes up. Say what rationality means before you criticise it. Then name the limitation by its proper name.
Shortcuts that usually work, until they do not
Working everything out is slow, so people use shortcuts. Each one is a bias: not stupidity, just a habit of mind that saves time and sometimes misleads.
| Bias | What it is | Example |
|---|---|---|
| Rule of thumb | deciding by habit, not calculation | I always buy this brand, so it must still be the best |
| Anchoring | the first number seen colours everything after | was €100, now €60 feels like a bargain, whatever it is worth |
| Framing | the same fact stated two ways gets two answers | 95% fat-free sells better than 5% fat |
| Availability | what comes to mind easily feels more likely | one news story makes a rare event feel common |
| Loss aversion | losing hurts about twice as much as winning pleases | holding a falling share rather than selling at a loss |
| Status quo bias | sticking with what you already have | staying on an expensive phone plan for years |
Important: Name it, explain it, and show it with an example. A definition without an example is half an answer. Then link it back: the point of a bias is that it breaks one of the model's assumptions.
Nudges: change the setup, not the rules
Choice architecture is how options are arranged: the order, the default, the labels. A nudge changes that arrangement to steer behaviour without banning anything or changing any price.
| Way to change behaviour | What it changes | Example |
|---|---|---|
| Tax or subsidy | the price of the choice | a sugar tax |
| Regulation or ban | removes an option | no smoking indoors |
| Nudge | the context of the choice, with options and prices untouched | pension auto-enrolment you can opt out of; calorie counts on menus |
For nudges: Cheap, compared with a tax or a subsidy.. Keeps freedom of choice: you can still opt out.. Can be very effective: pension take-up rose from about 50% to about 90% with auto-enrolment.. None of the side effects of a ban or a tax..
Against nudges: **Paternalism**: who decides what the right choice is?. Too weak for serious problems, such as addiction.. Firms nudge too, against you: the tricks built into websites to make you click.. Is it right for a government to steer citizens, even for their own good?.
Default: what happens if you do nothing. Restricted: some options removed. Mandated: one option required. Only the default is a pure nudge. If your policy bans something, it is regulation, so call it that.
Firms: profit is the assumption, not always the objective
The model assumes a firm produces where profit = total revenue − total cost is biggest: keep making units while each extra one earns more than it costs, and stop when the two are equal. That is the MR = MC rule, built properly in 2.11. Ask a real firm what it is aiming at, and few say maximum profit. Tap each objective.
Market share Sell the biggest possible share of the market, even at a lower price. Profit now is traded for pricing power later. Example: streaming services priced below cost for years to win subscribers.
Growth More outlets, more countries, more products. Size brings economies of scale and safety from takeover, and managers' pay usually follows size. Example: a chain opening a new branch every month while barely breaking even.
Corporate social responsibility Doing more for society and the environment than the law requires. It costs profit now and protects reputation, staff and customer loyalty later. Example: paying suppliers above the market rate and saying so on the packaging.
Satisficing Aiming for a result that is good enough rather than the best possible. Owners get an acceptable profit; managers get stability and a quieter life. Example: a family firm that never chases the extra sale if it means longer hours.
In a big company the owners (shareholders) are not the managers (employees). Shareholders want returns. Managers want job security, a bigger department and less risk, and the managers make the decisions. That separation is the sentence that turns a list of objectives into an explanation.
Worked examples
The three Paper 3 shapes this topic is asked in, with new scenarios. Try each before opening the plan.
A text describes shoppers who compare only two or three brands before choosing. Define the term bounded rationality.
Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
Now the Paper 3 explain.
Many people pay for a gym membership they rarely use. Explain how one limitation of rational consumer choice could account for this.
Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
And the Paper 3 recommend.
Recommend and justify a policy a government could use to cut household food waste.
Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
Quick self-check
Tap each card to check yourself.
State the three things the model assumes about a consumer. They maximise utility, they have full information, and they can rank every option and pick the best.
Define utility. The satisfaction a person gets from consuming a good or service. The thing a rational consumer is assumed to maximise.
A €900 phone shown first makes €600 feel cheap. Which bias? Anchoring. The first number seen colours every judgement after it.
'90% fat free' sells better than '10% fat'. Which bias? Framing. Same fact, two ways of saying it, two different reactions.
You know you should save and do not. Bounded rationality or bounded self-control? Bounded self-control. You know the better choice and do not make it. Bounded rationality is not being able to work out which choice is better.
Is a ban on plastic bags a nudge? No. A ban removes an option, so it is regulation. A charge changes the price, so it is a tax. A nudge leaves options and prices alone.
Why are default options so powerful? Because of status quo bias: most people stick with whatever happens if they do nothing. Make the good choice the default and doing nothing becomes choosing it.
Define satisficing. Aiming for a result that is good enough rather than the best possible. Consumers do it when comparing everything is too much work; firms do it when managers prefer a quiet life to maximum profit.
Exam tips
- Say what rationality means before you criticise it.
- Name the limitation by its proper name: bounded rationality, bounded self-control, bounded selfishness, imperfect information.
- Every bias: name it, explain it, give one example.
- A nudge leaves every option open and every price unchanged. If your policy bans or taxes, call it what it is.
- Recommend means choose one policy and defend it. Compare one alternative, then qualify.
- Name the bias the nudge works with. That is what makes the justification economics.
- Profit maximisation is an assumption. Questions here ask you to test it, not defend it. Owners versus managers is the explanation.