I Introduction Lawyers and legal philosophers have both recognized that our prevailing concepts of criminal responsibility and punishment depend upon a particular notion of personal identity, namely our possession of conscious minds to which are ascribed the qualities of unity, continuity through time, and the clear separation of each person from all others and the rest of the world. With the rebirth of interest in the philosophy of mind in the last twenty years, the nature of personal identity has again become philosophically important. The issue has gained philosophical notoriety with the publication in 1984 of Derek Parfit's Reasons and Persons. (1) Parfit's book contains a long and detailed argument that seeks to refute the common view of personal identity, namely, that an individual's identity is a special further fact additional to the sequence of that person's mental states. Although not the first, Parfit's work is one of the most sustained efforts to advocate a reductive theory of mind. Much of our moral practice, and most laws in most major legal systems, treat the individual as the fundamental unit of moral or legal responsibility. Indeed, moral or legal practice that appeals to notions of collective guilt or the punishment of communities is generally to be criticized. Further, individual responsibility is not usually thought to fade or shift with the passage of time. If, however, there are credible arguments for a reductive account of personal identity, then some of the central presumptions of individual responsibility that underpin our moral practice and the criminal law begin to unravel. This paper investigates some of the problems that this recent work creates for criminal law, particularly those concerned with an agent's continuing responsibility through time for criminal acts and specifically, with the role of memory in our assignment of such responsibility. A central argument of this paper is that, at the instant a person commits an immoral or criminal act, neither moral nor criminal responsibility should be assumed for all time. Liability to punishment depends upon the responsibility of the individual for that punishment continuing to be generated afresh throughout the period from commission of the offense to the completion of any sentence. The problem of explaining how moral or criminal responsibility continues through time has been a central focus of the debate regarding the nature of personal identity. Many of those who advocate a reductive theory of mind accept that, with the diminishing psychological connectedness of an offender's later selves from his earlier selves, moral responsibility may diminish. Thus many reductionists consider it true that someone does not deserve to be punished as severely for a crime he committed a long time ago as he does for a recently committed crime. For most mental reductionists, it is the overall qualitative change in a person's character, personality, and memories, that diminishes the extent of the person's responsibility for past acts. Non-reductionists would usually accept that acute mental illness seriously diminishes or terminates liability for punishment. Other than the absence of acute mental illness neither reductionists or non-reductionists have argued that any specific mental state is an essential condition for an offender continuing to be liable to punishment other than an offender's knowing why he is being punished. Contrary to the position adopted by most mental reductionists, I will argue that memories of doing a wrongful act, and of one's self and one's life at the time of doing of the act, are pre-conditions for being held responsible for that wrong, and hence liable for punishment. I argue that loss of memory of these matters relieves a person of moral responsibility for an act, even if he continues to share strong connections with the prior self who committed the wrong. Thus, an offender whose character, personality, and moral beliefs have remained substantially unchanged, and who still has substantial memories of most parts of his prior life, ought not to be liable for punishment if he has suffered a loss of memory with respect to the period of his life during which he committed a particular offense. …