Asking about personal identity and its implications are of central questions in metaphysics, philosophy of mind, and undoubtedly theology and eschatology. The essential components of this enquiry can be articulated by these questions: Who am I? What am I constituted of? What does differentiate me from others? How do I persist through time? Based on the responses to these enquiries various philosophical accounts of personal identity have been shaped: Substance Dualism, Property Dualism, Predicate Dualism, Continuity of Consciousness, Psychological Continuity, Bundle Theory, and No-Self Theory, to name a few. One of the essential problems in personal identity is identity persistence through time. This problem, which can be articulated as identicalness of an individual at time T1 to an individual at time T2, has significant implications for subsequent questions in the fields of ethics and philosophy of law. The proposed resolution for this problem brings out its practical consequences in ethics, agency, and responsibility.
In Western philosophy, Descartes is considered as who discussed the problem of personal identity in an early modern way, but the enquiry about identity persistence can be credited to John Locke by founding the memory theory of personal identity in his notable work ‘Essays Concerning Human Understanding’. Interestingly, for Locke the concept of personality pertained to forensic issues as he expressed that “Person is a forensic term”(Hume 1690, 120). It means that the importance of enquiries about personal identity and persistence are prerequisites for resolving the problem of moral and forensic responsibilities. In Locke’s view, it is sufficient for one to be morally responsible for an action if she has the same personal identity as the performer of that deed. Then he claimed that having the same consciousness is essential for the persistence of personal identity through time. For a person to have the same identity, Locke introduced a principle on ‘consciousness’ and its interrupter ‘forgetfulness’. This criterion that later became renowned as the 'Memory Criterion' of personal identity can be expressed as follows: person P2 at time T2 is identical to person P1 in earlier time T1 if P2 can remember sufficiently from what has happened to person P1 at T1 (Hume 1690, 115-116).
Thomas Reid, famous for his investigations on metaphysics of personal identity, criticised and rejected memory criterion by objecting that this criterion suffers from circularity. He argued that the memory criterion is neither sufficient nor necessary for the numerical persistence of one’s personal identity. His argument on rejecting the memory criterion can be articulated like this: for memory criterion to be plausible, any analysis of P2 to be the same person as P1 by remembering what happened to P1 at T1 entails identicalness of P2 and P1 as given. He also argued for intransitivity of memory by exemplifying a brave officer who captured a standard in his first battle but had been beaten when he was a schoolboy in his younger ages while officer later in his older ages became a general. Although the officer was conscious of having been beaten in school and although he as a general was conscious of been granted a standard because of hi bravery in his first battle, it is possible for him as a general not to remember his having been beaten in school. By this example, Reid showed that although personal identity is transitive by intuition, the memory criterion does not. Therefore, Lock’s account is contradictory (Reid 1785, 147-148). Before Reid, Joseph Butler in the first dissertation of his apologetics work ‘Analogy of Religion’ raised a similar objection on Lock’s account. He refused consciousness and memory to be constitutive of personal identity and claimed that consciousness does presuppose personal identity (Butler 1736, 222).
To respond to the circularity charge, Sydney Shoemaker introduced a modification to the memory criterion. To conciliate the memory criterion with transitivity, Shoemaker proposed the concept of quasi-memory or quasi-remembering (Shoemaker 1970). Derek Parfit made the second modification to the memory criterion by extending the scope of personal identity to human intention, future actions and responsibility. By these modifications, Parfit transferred the memory criterion into psychological continuity criterion (Parfit 1984). Although psychological continuity criterion resolved some issues that were persisted in previous accounts but encountered some counterintuitive contradictions, especially in answering hypothetical brain transplanting cases. In response to this objection, Parfit expressed that personal persistence is not essential, but it is the survival that is crucial for us (Parfit 1987).
In recent decades, our knwoledge about the nature and functionality of memory has been improved extensively. Nowadays we categorise human memory into three main types. The short-lasting one named sensory memory, which captures information from our five senses and keeps them enough to be transferred to the next type: short-term or working memory. The long-lasting type of memory named long-term memory that may last for the whole life. Long-term memory divides into implicit or procedural memory that is our unconscious memory, and explicit or declarative memory that is our conscious memory. Procedural memory contains memories of our skills and procedural tasks like riding a bicycle or playing piano. Declarative memory constitutes semantic memory that is for knowing and remembering facts and concepts; and episodic memory that is for remembering events and experiences. The episodic memory provides us an essential ability that is referred to by ‘autobiographic memory’ which is the capacity to remembering events in our life from the first person point of view.
The fundamental shift in our understanding of the functionality and the role of memory in personal identity happened when new empirical and introspective findings showed that our autobiographic memory is not like a warehouse of data. Memory, not like what some proponents of psychological continuity theory claimed, is not a mere depository of events and experiences, but it provide us with summarised, condensed story of our life as a coherent and consistent narrative from the first person point of view. It means that our recent findings of human’s memory do not support psychological continuity theory (Schechtman 1994).
In remembering a specific experience or event, it is my episodic memory that narrates my involvement and interaction with the world, which does not exist at present time. Therefore, this kind of memory shapes the conception of my personal life by proving the crucial ability of ‘mental time travel’, not only backwards in history but also forward to imagine the consequences of my decisions. This mental capability, which arises from the nature of the episodic memory, is fundamental for my ethical and forensic responsibility. Furthermore, in this view, for the persistence of identity neither complete nor accurate remembering of a past deed is needed, but only a robust causal connectedness between our experiences at time T1 in the past and psychological states at time T2, say at the moment, is required.
Many philosophical accounts of personal identity underline the importance of consciousness and memory in specifying the concepts of personal identity and persistence. Although we can follow back the path of enquiries about personal identity to many centuries ago, notable progress in our knowledge of different types of memory has extended these enquiries extensively in recent decades. This report has reviewed and analysed the outstanding accounts on personal identity and persistence with a focus on the role of memory in human agency and responsibility, as well as their practical consequences. Through the report, it has been claimed that personal identity consists of the body, psychological characteristics and memory. It has also been discussed that although episodic and autobiographic memory is central to a personal narrative of our life, our identity is not causally relied on them although they are crucial for personal identity, and ethical and forensic responsibilities.
Butler, Joseph. 1736. The analogy of religion, natural and revealed, to the constitution and course of nature: London: Printed for J.J. and P. Knapton.
Hume, David. 1690. Essays Concerning Human Understanding. Vol. Essay II. London.
Parfit, Derek. 1984. "What we believe ourselves to be." In Reasons and Persons.
Parfit, Derek. 1987. "Divided minds and the nature of persons." In Mindwaves: Thoughts on intelligence, identity, and consciousness, edited by Colin Blakemore and Susan Greenfield, 19-26. Oxford: Oxford.
Reid, Thomas. 1785. Essays on the intellectual powers of man Cambridge: Cambridge.
Schechtman, Marya. 1994. "The truth about memory." Philosophical Psychology 7 (1):3-18.
Shoemaker, Sydney. 1970. "Persons and Their Pasts." American Philosophical Quarterly 7 (4):269-285.