To continue the series on personal identity, we will consider the problems with the psychological criterion. It is probably the most widely held view of personal identity today thanks to its intuitive force. There have been two primary objections which have been ably answered, but they lead to more difficult questions.
To repeat the definition given in the last post, the psychological criterion holds that it is some form of psychological continuity, such as that expressed in memories, mental states or consciousness over time, that makes a person X at time t1 identical to something Y at time t2.
The first traditional objection was presented by Thomas Reid in response to the above formulation. (Remember from the last post that Locke was one of the original formulators of the psychological criterion, and so Reid is responding directly to him):
Suppose a brave officer to have been flogged when a boy at school for robbing an orchard, to have taken a standard from the enemy in his first campaign, and to have been made a general in advanced life; suppose, also, which must be admitted to be possible, that, when he took the standard, he was conscious of his having been flogged at school, and that, when made a general, he was conscious of his taking the standard, but had absolutely lost the consciousness of his flogging. These things being supposed, it follows, from Mr Locke’s doctrine, that he who was flogged at school is the same person who took the standard, and that he who took the standard is the same person who was made a general. Whence it follows, if there be any truth in logic, that the general is the same person with him who was flogged at school. But the general’s consciousness does not reach so far back as his flogging; therefore, according to Mr. Locke’s doctrine, he is not the person who was flogged. Therefore the general is, and at the same time is not, the same person with him who was flogged at school.
In other words, logic tells us that if a = b, and b = c, then a = c. But the psychological criterion suggests that even if a = b and b = c, a may not equal c. And this seems absurd. (Read Thomas Reid on personal identity here; essay III, chapter 3 in particular. The quote above is on pages 248 and 249.)
Second, Joseph Butler argued that the psychological criterion is circular:
…one should really think it self-evident, that consciousness of personal identity presupposes, and therefore cannot constitute, personal identity, any more than knowledge in any other case, can constitute truth, which it presupposes.
In other words, to say that memories (or other psychological connectedness) is evidence of personal identity is circular, because such psychological elements are exactly what personal identity consists in. So to insist on the psychological criterion is essentially to say “personal identity is the criterion of personal identity”, and that gets us nowhere. (Read Butler on personal identity here).
Against the first objection, Derek Parfit (among others) has offered a reformulation of the psychological criterion which focuses on indirect memory connections, instead of direct memory connections. If I remember being X, and if X remembers being Y, then that is enough for me to be psychologically continuous with Y. Or in Reid’s example above, the general can be the same as the boy flogged at school, because he remembers being the gallant officer who remembers being the boy.
Against the second objection, the response is to introduce a new concept like memory but without the link to identity: Parfit calls it quasi-memory. It may be self-contradictory to say that I remember doing something that someone else did, but I could still “quasi-remember” it.
There is a more serious objection that applies to the psychological criterion (whether or not you have reformulated it in response to the above objections). There are many times in the past to which I am not linked psychologically either directly or indirectly: for example, if I fall unconscious for a time, or even just sleep. Under the psychological criterion, at those times I cannot be identical with my past, conscious self! This seems wrong.
This objection leads to a further refinement to the criterion: that psychological continuity consists in saying that person X is psychologically continuous with person Y if the current mental states of X are so because of the mental states of Y. Therefore there is no need for a conscious appreciation of one’s current or past mental states, allowing for personal identity to continue through or despite periods of unconsciousness (for example).
However, the most fundamental objection to the psychological criterion is that of fission. If you are replicated, and a copy of you is present, under the psychological criterion we would have to say that both I and the copy are identical to a past person, X; but we would say that I and the copy are not identical to each other. How is this possible?
This leads to a range of responses, all of which seem odd to varying degrees. One response is to say that before the copy was made, there were essentially two copies of you residing in the one body, and so I and the copy are identical with the past halves of the original me. This seems bizarre to say the least. Another response is to say that my past self effectively dies, and two new people appear, when a copy is made; but this leads to the odd situation where my past self “dies” if both I and the copy survive, but if the copy dies, my past self seems to live.
This question of fission has led some, notably Parfit, to reject the notion of personal identity altogether – but that is a question for us to explore in the next post.
There are, of course, other objections (and responses) to the psychological criterion. Some focus on questions about how we relate as thinking persons to being physical, embodied creatures. The answers depend on metaphysical conclusions and questions considered by the philosophy of mind, which is beyond my sphere of expertise. For a comprehensive review of the above objections and others, I recommend the entry on personal identity at the Stanford Encyclopedia of Philosophy.