- Length
- 560 pagesOxford University Press, 1984, with corrections
- Reading
- OpenWritten for a general reader and readable without preparation
- Availability
- Many editionsIn print in several competing editions
Reasons and Persons
Five hundred pages arguing that we are wrong about what we are, wrong about what we owe the future, and that the second error follows from having no theory adequate to it. Parfit ends by stating a problem he spent the rest of his life failing to solve and says so.
- Date
- 1984
- Author
- Derek Parfit
- Region
- Oxford
- Language
- English
Where it stands in the argument
- Position
- Reply — Answers a named earlier work
- Form
- Treatise
- Method
- Analytic — Clarification of language and logical form
- Transmission
- Continuous — Copied and read without a break in its own language
- Standing
- Live — Still argued in current philosophical work
- Years back to what it answers
- 295 years
Widely regarded as the most important work of moral philosophy since Rawls, and the origin of population ethics as a field.
What the book says
Four parts, each dismantling something readers assume, held together by the claim that non-religious ethics is a young subject and that we are only beginning. The first argues that moral theories can be self-defeating: a theory telling each person to pursue their own interests produces outcomes worse for everyone by that theory's own standard, so it directs us to become people who do not follow it. The second treats rationality and time, attacking the assumption that a person should be indifferent between their own pains at different dates. The third is the famous one. Using thought experiments about teletransportation, brain division and gradual replacement, Parfit argues that personal identity is not what matters in survival: what matters is psychological continuity and connectedness, which can hold to different degrees and can hold between one person and two, so the question whether a future person would be me may have no determinate answer and need not. He calls this reductionism and says he found it liberating. The fourth part turns to future generations and reaches a conclusion he could not accept and could not refute.
What it argues
That the deep further fact we imagine about personal identity does not exist, and that a great deal follows. If what matters in survival is psychological continuity, and continuity is a matter of degree, then the boundary between persons is less deep than we suppose - which weakens the ground for special concern about one's own future and strengthens the case for concern about others. Parfit says he found this consoling: his own death became less bad, like a glass wall dissolving. The final part carries the argument into obligations to people who do not yet exist, and produces the repugnant conclusion: on any view that adds up wellbeing, a vast population with lives barely worth living outranks a smaller flourishing one. Parfit could not accept it, could not find a principle blocking it that avoided worse consequences, and left the problem open under the heading of a theory we do not yet have.
What it answered
Locke on personal identity, and the assumption running through ethics that the separateness of persons is a fixed starting point. He is also answering the self-interest theory of rationality, which he treats as an unstable hybrid, and the common-sense morality that permits us to weight our own futures and our own children heavily while ignoring people distant in space or time.
How it argues
By thought experiment, deployed at industrial scale. Teletransporters, split brains, gradual replacement of neurons, imagined populations of different sizes - the cases are numbered, refined and tested against each other in sequence, and the reader is asked at each step what they would say. The prose is plain and the structure is relentless. Parfit also does something rare: he states repeatedly where he has failed, and the book ends by naming an unsolved problem rather than a result.
The moment
Oxford, where Parfit was a fellow of All Souls for his entire career, worked continuously on a small number of problems, and was known for a working method of extreme intensity and for sending vast commentaries on other people's drafts. He photographed Venice and St Petersburg repeatedly, and cared, by his own account, about very little apart from the work.
How it travelled
Into three fields at once. Personal identity became a central topic in metaphysics again; population ethics was created as a discipline by the fourth part and is now substantial; and the arguments about future generations feed directly into work on climate policy, discount rates and long-term risk. Parfit's reductionism also connects to Buddhist views of the self, which he noted himself and which comparative philosophers have taken up.
The strongest objection
That the thought experiments prove less than the conclusions drawn from them. Teletransportation and brain division are cases far outside anything our concepts were formed to handle, and finding that they produce no determinate verdict may show a limit of the imagined scenario rather than a truth about what we are. Williams pressed a version of this: our concern for our own future is not obviously a belief that could be shown false by a puzzle case, and describing it as an error about metaphysics may misdescribe what kind of thing it is. Parfit's answer is that the cases only make vivid what is already true of ordinary gradual change, which is a real reply and turns on whether the ordinary case really has the structure the exotic one displays.
Why read it
Part three, which is the most gripping stretch of analytic philosophy written in the last fifty years and can be read alone. Part four for the repugnant conclusion, which anyone thinking about future generations has to face. The first two parts are harder going and less discussed. No background needed.
- First printed
- 1984
- First in English
- 1984
- Digitised
- No
Parfit continued correcting the text through successive impressions. On What Matters, in three volumes from 2011, takes up the question of whether the major moral theories converge and is a separate project.
Written in English and translated widely. In copyright.
Where it stands
Live and unusually productive. The repugnant conclusion has generated a literature of its own and remains unsolved; impossibility results published since suggest that no theory of population ethics can satisfy all the constraints Parfit wanted, which is a formal vindication of his failure.
On quoting this book
In copyright. Nothing is quoted.
Contested
Whether the reductionist view of persons is correct, and whether it has the practical consequences Parfit draws, is argued continuously. Whether the repugnant conclusion is genuinely repugnant, or a case where intuition should give way, divides population ethicists and a substantial group now accepts it. How far Parfit's later convergence project in On What Matters is consistent with this book is debated. And whether his own report that reductionism made his death less frightening is evidence for anything, or a fact about him, is a question readers answer differently.