Personal Identity

What is a person?

 1.     An individual human being

2. An individual’s body

3. From the Latin word persona meaning “actor’s mask”

Those are the official definitions, but in philosophy we explore this more.

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  • Created by: Amy
  • Created on: 07-05-12 19:54

What is a person?

Gottlob Frege (1848-1925) spoke of the difference between the sense and reference of a word.  A person and a human being have the same reference, but they do not have the same sense.

To be a person, it is said that we need to aquire attributes of personhood.

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Attributes of personhood

There are many, but I've cut it down to remember them:

  • Possessing a network of beliefs: beliving in God, having superstitions and personal and social values
  • Creativity - humans produce writing and art to express themselves. This attribute it not often seen in animals. however, some elephants are able to produce artistic paintings
  • Responsibility: Having a duty to deal with something. We must use our morals to make decisions that can affect ourselves or other people. We weigh up the good and bad; so that the outcome is the consequence we want. Also, being autonomous
  • Motives - reasoning behind the action performed. For criminals, jealousy or rage leads to murder. For animals, they make a noise when they want something
  • If you are a "social being", you have the ability to communicate and socialise with other people around you. You will also conform to the values of society. However, many people cannot perform this and many animals can; as most travel in groups, mate with and groom each other.
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Personhood by degree

Diminished person: 

someone who has Alzheimer’s , or a disease like that, who have continually lost their personhood and become a husk


Someone who has completely lost their personhood. E.g. vegetative states and death.

Potential person:

Not yet a person, but will grow to obtain and expand on the characteristics to which we define in a person e.g. a babyNot yet a person, but will grow to obtain and expand on the characteristics to which we define in a person e.g. a baby or embryo

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What is a person? - Locke and Singer

John Locke:

A person is a "thinking and intelligent being that has reason and reflection, and consider itself as itself, the same thinking thing, in different times and places.

Peter Singer:

He then added "self awareness, self control, a sense of past and future, the capacity to relate to others, concern for others & communication and curiosity"


1.       I think that self-awareness is important in order to contribute to personhood. To know who you are, your family ties, your personality; that must be prominent and understood, otherwise your existence is vague and you are just drifting through life not knowing who you truly are.

2.       Specieism is where you put members of your own species before other species. For example, most of us would save a human rather than another animal.

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Could a machine ever be a person?

Science fiction frequently portrays ‘thinking’ machines, from computers that perform basic tasks, to robots with simulated emotions and appear to act in a way that is indistinguishable with human beings. (DATA, bicentennial man, etc)

1.       The Turing Test was developed by computer genius Alan Turing. He stated that if you can converse with an artificial being – a robot – freely, and are fooled into thinking it is a human or a person, then that artificial being would be classed as a person. This has not been achieved, yet there are many artificial beings being made – such as Milo (who can remind you of your mother's birthday) – and perhaps one day in the future we can achieve this.

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Personal Identity through time

Heraclitus wrote, ‘You cannot step twice into the same river; for other waters are continually flowing in’. This can then be related back to humans; as our personality changes as external factors affect us, we grow, we lose and regain skin cells.

Obviously our physical appearance changes considerably over a period of time, but we also develop mentally.

Throughout our lives we are continualy subject to external influences that cause us to change our perspectives on the world.  Just as increased knowledge on an issue might cause you to revise your opinions, so too will attitudes change as we grow and develop.

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Personal Identity through time

What cannot be denied, is that although our bodily appearance changes, there are still certain aspects which remain fixed – DNA and fingerprints for example.  Similarly, although our opinions and attitudes might change over time, it could be argued that we still have the same basic character.

There are two aspects of personal identity through time: psychological and physical.

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Physical continuity through time

Is physical continuity necessary? (do we need it)

  • Yes, legal matters
  • Yes, Recognition of others
  • No, age changes
  • No, Cosmetic changes

For many, numerical identity (Being exactly the same person, but with different qualities) is what constitutes personal identity.  In other words, you are the same person that you were when you were a baby, because although you have altered a lot ‘qualitatively’, or physically, you are still numerically identical with that baby.

 The philosophical formula for this would be:

A person P1 at time t1 is identical with a person P0 at an earlier time of t0 iff (if and only if) P1 is physically continuous with P0. 

P1 = Helen  t1 = 2/12/11 & P0 = Helen 2  t0 = 2/12/10

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Physical continuity through time

In simple terms, a person is the same if they have one and the same body that they had in the past. This theory takes into account that we are continually changing – shedding skin etc. Although qualitatively our adult body is very different from our childhood, we are still the same person. 

Necessary Conditions

A condition which it is required to have in order to be something. (e.g. it is necessary to be warm-blooded to be a horse) but having that condition (being warm-blooded) is not the only quality needed (to be a horse. It is possible to be warm-blooded and not be a horse.)

Sufficient Conditions

Conditions can be sufficient but not necessary. It fulfils the criteria of being British if you are born in Britain; however, there are other conditions which would make someone equally British (e.g. marriage).

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Problems with physical continuity

Physical continuity isn’t a necessary condition of identity. We can conceive of attributing identity through time where physical continuity isn’t satisfied.

Physical continuity isn’t a sufficient condition of identity. We can conceive of refusing to attribute identity through time where physical continuity is satisfied.

The continued existence of the whole body isn’t required for identity through time, only the continued existence of the brain: but is the continued existence of the whole brain necessary or sufficient for identity?  (Wiggins & Parfit)

The continued existence of the brain (or part of it) won’t give identity through time if mentality isn’t reducible to the functioning of the brain.

Derek Parfit claimed that it is possible to continue being the same person despite a lack of physical continuity, something which would be supported by many religious groups who believe in an afterlife.  For Parfit, it is not necessary to be able to continuously  trace your physical body if your mentality remains unchanged.

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Problems with physical continuity - Examples

Parfit imagines a Star Trek scenario, where he presses a button and shall lose consciousness, then the scanner of earth will destroy his brain and body and record his cells. The scanner will then transmit this information by radio and the message will take 3 minutes to reach the replicator on Mars. This could create, out of new matter, a brain and body exactly like his

Shoemaker imagined a scenario where two men, Mr Brown and Mr Robinson were having an operation for brain tumours where brain extractions had taken place. However, the assistant inadvertently put Brown’s brain into Robinson’s head and Robinson’s brain into Brown’s head. One of the men died (Brown's body & Robinson's brain), but the other, the one with Robinson’s head and Brown’s brain, eventually regains consciousness. We shall call this man ‘Brownson’. When asked his name he automatically replies ‘Brown’ and he can recognise Brown’s wife and family.  

Theseus' Ship - if the boards get rotten and need replacing, and they do, plank by plank, is the new ship - made of completely different planks - still Theseus' ship? Moreover, if we make a new ship out of the old planks, which one is Theseus' ship?

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Psychological continuity through time

John Locke considered that it is a person’s consciousness that determines personal identity.

In other words, if we are conscious of behaving in a particular way in the past, then we are the same as that person.  For many this has been simplified to a question of memory – if I remember doing something, then I must have been the same person who did it

. Physical continuity of the brain is only important as long as it ensured the psychological continuity of the person’s mental life

A person with a total loss of memory effectively becomes a numerically different person

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Psychological continuity through time - Criticisms

As early as the 18th Century Locke’s theory came under criticismThomas Reid (1710 – 1796) highlighted a flaw by giving an example of a brave ensign.  Briefly the situation is as follows:


  1. An ensign remembers stealing apples as a boy
  2. As a general, he remembers taking the standard (flag) as an ensign
  3. But the general cannot remember stealing apples as a boy

Reid’s example indicates that the general is the same person as the ensign, but not the same person as the schoolboy, and yet the ensign is the same person as the schoolboy.  Therefore we have a contradiction.

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Derek Parfit reflected on “overlapping memory chains”. – Continuity and Connectivist theory

If the general remembers a time which is remembered being a boy (the ensign), then he is the same person as the boy.

P2 remembers being P1. P1 remembers being P0. Therefore, P2 is the same person as P0 despite not being able to remember being him.

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Perhaps the most sensible approach is that taken by Bishop Joseph Butler (1692-1752), who claimed that personal identity depends on both physical and psychological continuity.  If I remember doing an action, and at the same time remember being the same person doing that action, then I am the same person.

Butler claims Locke’s argument is circular. “Consciousness of personal ID presupposes and therefore cannot constitute personal identity”. As you must be conscious to have an ID. In stating that consciousness is necessary presupposes there is someone to be conscious. You can’t use consciousness to explain personal ID, because consciousness depends on personal ID. Parfit’s response is that a person can be described in impersonal terms e.g. a combination of experiences, thoughts and actions.

J.L Mackie considers that it is best to regard the identities of person in this world as dependent upon those material structures that underpin and preserve the continuity of a person’s psychological capacities, especially memory.

-You need your psychical body, but not all of it. It’s not essential.

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Wiggins & Parfit

 Florence example: Florence’s brain is divided into two hemispheres and each is placed into an empty skull. The two Florences have full memories and refer to themselves in the first person as Florence – so which one is Florence?

Possible answer: ‘personal survival without identity’ i.e. Florence survives, but is not numerically identical with either Florence.

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Necessary and Sufficient conditions

Necessary Conditions:

Being at least 18 years of age is a condition of being eligible to vote in Britain.

What this means is that someone HAS to be 18 in order to vote. And if that person is not at least 18, they cannot vote. This is termed as a necessary condition because it is necessary that one be at least 18 if one hopes to vote. 

Note what this sentence does NOT mean. It does not mean that if you are 18 you will automatically be able to vote; because it is quite possible you'll be debarred from voting for some other reason. (e.g. prisoner or insane or a dog). So while being 18 is one condition it is not the only condition. 

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Sufficient Conditions:

Having your head chopped off is a condition for dying.

If you have your head chopped off, you will die. This is a sufficient condition since losing your head is enough, or sufficient, for dying.

Note what this sentence does not mean. It does not mean that if one has not had one's head chopped off then one is not dead. For it is quite possible to die by any other means. So you don't have to have your head chopped off in order to die. 

In other words, losing your head is not a necessary condition for death, but it is a sufficient condition.

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1. Being Human - Not necessary (you don't have to be a human to be a person) & not sufficient (a human does not have to be a person - corpse or zygote)

2. Being able to reason - 

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