Scarcity, choice and opportunity cost

Imagine a completely free afternoon. Even without a cash expense, you cannot spend the same hour sleeping, visiting a friend and learning a skill in different places. Time is scarce because its uses compete. Wealth can relax some constraints, but it does not remove all of them. Economics begins by identifying the decision-maker, the available alternatives and the limits on those alternatives. This course pays particular attention to individual agency and voluntary arrangements. That interest does not settle every factual question: we must still examine evidence, assumptions and the consequences of different choices.

Suppose a learner wants to take three evening classes. Enough money is not sufficient if all three meet at the same time. Equally, an available timetable is not enough if a required prerequisite is missing. Write down each relevant constraint before recommending a choice. A constraint is binding at a particular choice when that choice uses the entire stated limit; a non-binding constraint has slack. Some models simplify this to money alone. That can be useful, provided we remember that the model deliberately leaves out other limits rather than proving that they do not exist.

Step one is to name the quantities and their units: books and lunches per week. Step two is to multiply each quantity by its price. Two books cost 2 times £9, or £18; three lunches cost 3 times £6, also £18. Step three adds those expenditures: £36, so that bundle is feasible and lies on the budget boundary. One book and three lunches cost £27, leaving £9 unspent. Four books and one lunch cost £42, so that bundle is infeasible under the stated budget. We are holding prices fixed and allowing no borrowing.

Divide the book price by the lunch price: 9 divided by 6 equals 1.5 lunches per book. Check the units: pounds per book divided by pounds per lunch becomes lunches per book. Because half a lunch may not be purchasable, compare whole bundles as well. Starting from two books and three lunches, moving to four books and zero lunches gains two books and sacrifices three lunches. The ratio is still three divided by two. Whether that change is desirable depends on the learner’s priorities. Feasibility and desirability are separate questions.

List the alternatives before calculating anything. Tutoring and gardening cannot both occupy the same hour, so adding their earnings invents an opportunity that never existed. Non-cash alternatives also count. Someone might value resting above either paid activity. We cannot discover that ranking from wages alone. When we express benefits in pounds, we are using a stated or estimated money equivalent for this particular person, not claiming that every experience has a publicly observable price. Opportunity costs may differ between people facing the same shop prices because their alternatives and priorities differ.

Suppose making a shelf costs £14 for materials and takes an afternoon that could otherwise earn £40 after relevant work expenses. Under these illustrative assumptions, the economic cost is £54. Calling the labour unpaid does not make its opportunity cost zero. However, if you compare the project’s net outcome directly with the £40 work alternative, do not subtract £40 again on the other side. Consistent comparisons can use total outcomes or incremental differences. Both methods should give the same ranking when they include the same alternatives and avoid counting a sacrifice twice.

The practical test is not simply whether money has already changed hands. Ask whether choosing differently now would recover any of it. A non-refundable ticket has a sunk purchase price. A ticket that can be resold has a current opportunity cost: using it sacrifices its net resale value. An unpaid cancellation charge may also be an avoidable future cost. Decisions should reflect those differences. Ignoring a genuinely sunk cost does not excuse the original decision or prevent learning from it; it means refusing to let an irreversible past loss distort the present comparison.

Step one removes the £18 ticket payment from both current alternatives because neither decision can recover it. Step two calculates attending’s future net value: £25 minus £8 equals £17. Step three compares that with the £14 home alternative. The difference is £3 in favour of attending, given these stated valuations. If illness reduced concert enjoyment to £19, attending would instead give £11 and staying home would be preferable. The ticket price remains unchanged in both cases. The example demonstrates a decision rule; it does not prescribe how much anyone should enjoy music or rest.

A first glass of water may be extremely valuable, while a tenth glass in the same sitting may not be welcome. Total benefit and the benefit of the next glass answer different questions. Marginal reasoning focuses on the choice that remains open now. It is especially useful when deciding how much of an activity to do. The simple rule needs care when choices come in bundles, require a minimum scale, or affect future opportunities. In those cases, compare complete feasible plans rather than mechanically applying a one-unit rule that ignores connections between decisions.

First calculate each extra session separately: 31 minus 15 is 16; 22 minus 15 is 7; 12 minus 15 is negative 3; and 5 minus 15 is negative 10. Then build feasible totals. Zero sessions gives zero; one gives 16; two give 23; three give 20; and four give 10. Two sessions is best among these options. This conclusion assumes sessions are taken in order, the stated benefits include relevant consequences, and no separate package discount applies. An earlier non-refundable enrolment fee would not change this current choice if it cannot be recovered.

Imagine that completing all four sessions produces a certificate worth an additional £30 to the learner. That changes the fourth session’s consequences and therefore changes the original calculation. The earlier conclusion was not mathematically wrong; its assumptions no longer describe the choice. This is why good economic reasoning records the conditions behind a result. A model can make a complex question manageable, but simplicity is a tool rather than proof of universal validity. Ask which omitted feature could reverse the ranking, then investigate that feature instead of adding detail that cannot affect the decision.

Suppose an activity has a one-half chance of delivering a benefit valued at £40 and a one-half chance of delivering zero. Its expected benefit is £20, calculated as one-half times 40 plus one-half times zero. That does not mean everyone would exchange a certain £20 for this gamble. Preferences over risk and the ability to absorb a bad outcome matter. Estimates of probabilities can also be poor. Treat expected value as one transparent component of a decision, state where the probabilities came from, and avoid presenting an uncertain forecast as a guaranteed outcome.

A libertarian approach typically gives substantial weight to individual liberty, property rights and voluntary cooperation. We can examine that position openly while distinguishing it from a prediction. For example, saying that adults should generally direct their own lives is a value judgement. Saying that a new restriction raises a particular cost is a causal claim requiring a mechanism and evidence. A person's choice reveals something about their ranking among perceived options, but it does not establish perfect information, freedom from pressure, or effects on other people. Keep those questions visible rather than assuming them away.

Use the checklist on a modest decision before applying it to a complicated policy debate. A clear comparison of two available study plans can teach more than a confident claim about an entire economy with no stated assumptions. Notice where arithmetic ends and judgement begins. The calculations organise implications of the information supplied; they cannot create missing preferences or reliable probabilities. In the exercises, numerical and choice responses can be checked automatically. Short written explanations are explicitly ungraded reflection. Use them to state an assumption or limitation, not to guess a hidden keyword that supposedly proves understanding.