Limitations of the theory
Definition
Cardinal utility: satisfaction measured in countable units (utils) that can be added and compared.
Rational behaviour: the assumption that a consumer weighs costs and benefits to maximise their own utility consistently.
Behavioural economics: the study of how real choices depart from this rational model, using heuristics and biases.
These two assumptions do a lot of heavy lifting, so testing them shows how far the model can be trusted.
Main limitations
- Utility cannot really be measured in cardinal units, so the exact util figures are only notional.
- Consumers do not always behave rationally, so their choices need not maximise utility.
- Habit and impulse mean the last unit is not always weighed against its price.
- Imperfect information and the influence of others distort the marginal utility a buyer perceives.
Example
- A shopper with a £50 grocery budget rarely computes the utility per £ of each item.
- Chocolate placed at the till triggers a £3 impulse buy that no utility calculation predicted.
- With limited information on quality, they may pay £4 for a coffee that adds little extra satisfaction.
Bridge to behavioural economics
- Behavioural economics studies these departures from rational choice.
- It highlights heuristics (rules of thumb) and biases that shortcut the utility calculation.
- It explains why real choices differ from the model's predictions.
- So the theory points beyond itself towards a richer account of behaviour.
Note
- Shoppers may buy on impulse near the till.
- They may follow what others are buying.
- So behaviour departs from strict utility maximisation.
Weighing it up
- For the theory: it gives a clear, logical account of why demand slopes down.
- Against: measurable utility and full rationality are unrealistic assumptions.
- It ignores habit, imperfect information and social influence.
- On balance it is a useful model rather than fact, and its accuracy is a matter of degree. It predicts well for frequent, low-stakes, repeat purchases where prices are clear and buyers learn from experience, but poorly for one-off, high-emotion, addictive or heavily-marketed goods where habit and bias dominate. So how far it holds depends on the good and the buyer.
Exam technique
- Set out the assumptions of measurable utility and rationality.
- Explain why each is questionable.
- Present the theory as a model, not fact.
Common Mistake
- Do not present the theory as fact.
- It is a model resting on strong assumptions.
Self review
- What does the theory assume about utility?
- What does it assume about consumers?
- Name two real-world factors it ignores.
- How does it link to behavioural economics?
- Why treat it as a model rather than fact?
