Key Arguments

• He identifies 'Contributor’s Dilemmas' as 'the commonest true Dilemmas' and defines them as involving 'public goods: outcomes that benefit even those who do not help to produce them.' In such cases, 'It can be true of each person that, if he helps, he will add to the sum of benefits, or expected benefits. But only a very small portion of the benefit he adds will come back to him.' This structure makes free‑riding rational from each individual’s standpoint.
• Because each receives only a tiny fraction of the marginal benefit they create, 'Since his share of what he adds will be very small, it may not repay his contribution. It may thus be better for each if he does not contribute. This can be so whatever others do.' Yet 'it will be worse for each if fewer others contribute. And if none contribute this will be worse for each than if all do.' This directly parallels his many‑person dilemma definition and shows the conflict between S and group welfare.
• He notes that many Contributor’s Dilemmas involve 'two thresholds'—numbers v and w such that 'if fewer than v contribute, no benefit will be produced, and if more than w contribute, this will not increase the benefit produced.' This creates a non‑linear public‑good production function where individual contributions matter only in aggregate, further weakening each agent’s incentive.
• In many such threshold cases we lack information about others' behaviour, so 'It will then not be certain that, if anyone contributes, he will benefit others. It will be true only that he will give to others an expected benefit.' This links Contributor’s Dilemmas to his earlier notion of Risky Dilemmas based on expected benefits.
• He gives voting as an 'extreme case' of a threshold public good: 'the gap between the two thresholds may be the gap of a single vote. The number w is here v + 1.' The benefit (a better government) is public, but each individual vote has only a minuscule expected impact, so Self‑interest Theory tempts citizens to abstain even when universal abstention would be far worse.
• He lists several concrete public‑goods/avoidance‑of‑evil scenarios: commuters choosing between driving or buses, soldiers deciding whether to stand or run, fishermen overfishing, and peasants having more children on overcrowded land. In each, 'It can be better for each' to make the self‑interested choice (drive, run, catch more, have more children), but 'worse for each if all do' likewise.
• He notes that 'There are countless other cases. It can be better for each if he adds to pollution, uses more energy, jumps queues, and breaks agreements; but, if all do these things, that can be worse for each than if none do.' These examples demonstrate the ubiquity of Contributor’s Dilemmas in modern life, particularly in environmental and social‑coordination contexts.
• In the broader argumentative context of the chapter, these Contributor’s Dilemmas exemplify how, under the Self‑interest Theory, 'if each rather than none of us does what will be better for himself, this will be worse for everyone', showing a pervasive direct collective self‑defeat of S in the presence of public goods and large populations.

Source Quotes

It may affect what a few others do; but this would seldom make enough difference. The commonest true Dilemmas are Contributor’s Dilemmas. These involve public goods: outcomes that benefit even those who do not help to produce them. It can be true of each person that, if he helps, he will add to the sum of benefits, or expected benefits.

These involve public goods: outcomes that benefit even those who do not help to produce them. It can be true of each person that, if he helps, he will add to the sum of benefits, or expected benefits. But only a very small portion of the benefit he adds will come back to him. Since his share of what he adds will be very small, it may not repay his contribution.

But only a very small portion of the benefit he adds will come back to him. Since his share of what he adds will be very small, it may not repay his contribution. It may thus be better for each if he does not contribute. This can be so whatever others do. But it will be worse for each if fewer others contribute. And if none contribute this will be worse for each than if all do. Many Contributor’s Dilemmas involve two thresholds.

And if none contribute this will be worse for each than if all do. Many Contributor’s Dilemmas involve two thresholds. In these cases, there are two numbers v and w such that, if fewer than v contribute, no benefit will be produced, and if more than w contribute, this will not increase the benefit produced. In many of these cases we do not know what others are likely to do.

In these cases, there are two numbers v and w such that, if fewer than v contribute, no benefit will be produced, and if more than w contribute, this will not increase the benefit produced. In many of these cases we do not know what others are likely to do. It will then not be certain that, if anyone contributes, he will benefit others. It will be true only that he will give to others an expected benefit. One extreme case is that of voting, where the gap between the two thresholds may be the gap of a single vote.

It will be true only that he will give to others an expected benefit. One extreme case is that of voting, where the gap between the two thresholds may be the gap of a single vote. The number w is here v + 1. Though an election is seldom a true Prisoner’s Dilemma, it will be worth discussing later.

The same can be true for peasants on collective farms. A third kind of public good is the avoidance of an evil. The contribution needed here is often self-restraint. Such cases may involve Commuters: Each goes faster if he drives, but if all drive each goes slower than if all take buses; Soldiers: Each will be safer if he turns and runs, but if all do more will be killed than if none do; Fishermen: When the sea is overfished, it can be better for each if he tries to catch more, worse for each if all do; Peasants: When the land is overcrowded, it can be better for each if he or she has more children, worse for each if all do.32 There are countless other cases. It can be better for each if he adds to pollution, uses more energy, jumps queues, and breaks agreements; but, if all do these things, that can be worse for each than if none do.

The contribution needed here is often self-restraint. Such cases may involve Commuters: Each goes faster if he drives, but if all drive each goes slower than if all take buses; Soldiers: Each will be safer if he turns and runs, but if all do more will be killed than if none do; Fishermen: When the sea is overfished, it can be better for each if he tries to catch more, worse for each if all do; Peasants: When the land is overcrowded, it can be better for each if he or she has more children, worse for each if all do.32 There are countless other cases. It can be better for each if he adds to pollution, uses more energy, jumps queues, and breaks agreements; but, if all do these things, that can be worse for each than if none do. It is very often true that, if each rather than none does what will be better for himself, this will be worse for everyone.

Key Concepts

• The commonest true Dilemmas are Contributor’s Dilemmas. These involve public goods: outcomes that benefit even those who do not help to produce them.
• It can be true of each person that, if he helps, he will add to the sum of benefits, or expected benefits. But only a very small portion of the benefit he adds will come back to him.
• Since his share of what he adds will be very small, it may not repay his contribution. It may thus be better for each if he does not contribute. This can be so whatever others do. But it will be worse for each if fewer others contribute. And if none contribute this will be worse for each than if all do.
• Many Contributor’s Dilemmas involve two thresholds. In these cases, there are two numbers v and w such that, if fewer than v contribute, no benefit will be produced, and if more than w contribute, this will not increase the benefit produced.
• In many of these cases we do not know what others are likely to do. It will then not be certain that, if anyone contributes, he will benefit others. It will be true only that he will give to others an expected benefit.
• One extreme case is that of voting, where the gap between the two thresholds may be the gap of a single vote. The number w is here v + 1.
• A third kind of public good is the avoidance of an evil. The contribution needed here is often self-restraint. Such cases may involve Commuters: Each goes faster if he drives, but if all drive each goes slower than if all take buses; Soldiers: Each will be safer if he turns and runs, but if all do more will be killed than if none do; Fishermen: When the sea is overfished, it can be better for each if he tries to catch more, worse for each if all do; Peasants: When the land is overcrowded, it can be better for each if he or she has more children, worse for each if all do.
• There are countless other cases. It can be better for each if he adds to pollution, uses more energy, jumps queues, and breaks agreements; but, if all do these things, that can be worse for each than if none do.

Context

Later part of section 23, where Parfit applies his many‑person dilemma framework to public goods and threshold cases, introduces Contributor’s Dilemmas as paradigmatic, and illustrates them with examples like voting, pollution, commuting, military courage, overfishing, and fertility under overcrowding.