Philosophy › Contemporary › Applied ethics (bioethics, animals, global poverty)
Derek Parfit, Reasons and Persons
1942–2017· Philosopher· Ethics & how to live
Well documentedSolid records, texts or physical evidence.
Oxford philosopher whose Reasons and Persons (1984) argued that personal identity matters less than we think, and founded the ethics of future populations.
See it on the Philosophy map →The idea
Idea: what matters in survival is psychological connection, not a deep further fact of 'being the same person'. Using teleporters and split brains, he argued identity can be indeterminate (see the personal identity question). He also posed the 'non-identity problem': today's policies change who will be born, so how can a future person be harmed by choices without which they would not exist? And the 'repugnant conclusion' about huge, barely happy populations. Main objection: critics say identity still matters for responsibility and self-concern.
Why it matters
It founded modern population ethics, the ethics of choices that affect how many and which people will exist, and influenced effective altruism and longtermism.
Legacy and sources
Reasons and Persons (1984), which includes an appendix on the Buddha's view, and On What Matters (three volumes, 2011–2017). He spent nearly his whole career at All Souls College, Oxford.
Still debated
No one has found a population ethics that avoids the repugnant conclusion without other strange results; Parfit himself called the problem unsolved.
Connections (3)
▸No-self (anatta) and impermanence anticipated the personal-identity view of Derek Parfit, Reasons and PersonsMostly agreed
The connection
The Buddha taught that the self is a changing bundle of processes with no permanent core. Parfit reached a similar conclusion through thought experiments: there is no deep further fact about personal identity, only degrees of psychological connection. He noticed the parallel himself and said the Buddha would have agreed with him.
When and how
Oxford, 1984: Parfit, a fellow of All Souls College, made the comparison in Reasons and Persons, Appendix J, quoting classical Buddhist texts.
How sure are we?
Parfit's own appendix states the parallel; scholars of Buddhist philosophy, notably Mark Siderits in Personal Identity and Buddhist Philosophy (2003), have since compared the two views in detail.
Debates and open questions
Parfit reached his view independently, so this is a parallel more than an influence; how close the views are is debated, since Buddhism ties no-self to rebirth and liberation.
▸Derek Parfit, Reasons and Persons inspired Effective altruism and longtermismMostly agreed
The connection
Parfit argued that future people matter morally as much as present ones. He ended Reasons and Persons comparing peace, a war killing 99% of humanity, and one killing everyone: the last step is far worse, because it ends all future lives. Longtermism grew from that thought.
When and how
Reasons and Persons (1984), final chapter; Parfit's Oxford colleagues, among them Toby Ord and Will MacAskill, founded effective altruist groups there from 2009.
How sure are we?
Ord and MacAskill credit Parfit directly, and his 99% versus 100% passage is often quoted as longtermism's root, though Parfit was not a movement leader.
Debates and open questions
Parfit's own 'repugnant conclusion' shows how hard it is to value future people; whether longtermism has solved those puzzles or set them aside is debated.
▸What makes you the same person over time? was radically reframed by Derek Parfit, Reasons and PersonsWell documented
The connection
Parfit argued that personal identity is not what matters. Using cases like a teleporter that destroys you and builds an exact copy on Mars, or a brain split between two bodies, he concluded that what we should care about is psychological connection, which comes in degrees. He found this freeing: less fear of death, more concern for others.
When and how
Reasons and Persons, Part 3, published in 1984 while Parfit was a fellow of All Souls College, Oxford.
How we know
Reasons and Persons is widely ranked among the most important 20th-century works of philosophy, and its cases are standard in courses on the self.
Debates and open questions
Critics argue identity does matter, for responsibility and survival, and question whether Parfit's view supports impartial ethics as he claimed.