When Russell claims that episodic memory is at the heart of our understanding of the past, he writes that this is because episodic memory gives us ‘immediate knowledge’ of the past (2001, p. 26). Similarly, Hoerl (1999, p. 246) argues that episodic memory is central to possessing a concept of the past because episodic memories make one ‘directly aware of […] the fact that past events impose certain constraints on the present’. These claims of ‘direct’ or ‘immediate awareness’ suggest a view of episodic memory according to which having episodic memory is sufficient for possessing a concept of the past. But the account of episodic memory as event memory, offered in Sect. 3, makes this view difficult to sustain. On that view, it is not clear why one ought to think that an episodic memory of an event will wear its causal or temporal connection to the present on its sleeve, such that the temporal or causal relationship a remembered event stands into the present will be transparent to the remembering subject.
The issue is not with the idea that episodic memory involves ‘immediate’ or ‘direct’ awareness of a remembered event. Let’s take ‘immediate’ or ‘direct’ to mean something like ‘not mediated by inference’, and let’s grant for the sake of argument that episodic memory provides immediate or direct awareness to remembered events. What is not clear is why we should think that episodic memories provide immediate or direct awareness of precisely this feature of a remembered event: that it occurred at some (particular) past time and constrains the present. This is not obvious because episodic memories are spatial scene constructions, which need not contain temporal information. Of course, many episodic memories do have what we might call an ‘internal’ temporal structure, which is to say that they may carry information about the remembered event’s duration or the order in which its constituent parts occurred (see Boyle 2019b; Cheng and Werning 2016). So, insofar as they provide direct access to remembered events, it’s reasonable to take them to provide direct access to these internal temporal properties. It is quite another thing to suppose that, in remembering, one is directly aware of what we might call an event’s external temporal properties—that is, where in time the remembered event is situated. This just isn’t central to what episodic memories are, on the account I’ve offered.
One might be tempted to treat this as an oversight in that account: perhaps we should add that episodic memories provide for a direct awareness of events as having occurred at some (particular) past time. But in fact, there are good reasons for not taking direct awareness of external temporal properties to be a characteristic feature of episodic memory. First, there are clearly a great many cases in which we have episodic memories for events we are unable to temporally locate. I have a certain memory of taking a trip to the beach, but could not tell you when this happened. Second, insofar as we are able to locate remembered events in time, this is unlikely to be because memories make one directly aware of a remembered event’s external temporal properties. Rather, it is because we are able to exploit our general knowledge about temporal patterns and about our life history, and use contextual information provided by the memory to infer its location in time (Friedman 1993, p. 58). For instance, I know that when I fell over and skinned my knee, I must have been between the ages of two and seven, since this memory unfolds in the garden of a house I know I only lived in between those ages. But my memory of the beach trip is sparse, and provides me with no contextual cues I can use to locate it in time.
Of course, one might point out that I am still at least able to say that this beach trip happened at some point in the past—I know that my representation of this event is not the product of imagination. This is true—but it’s again unclear that this is to be explained in terms of an immediate or direct awareness of the pastness of the event, such that any subject who had this memory would necessarily recognise the remembered event as belonging to the past. Whilst my memory may have a phenomenal quality that my imaginings typically lack, as a result of which I am inclined to believe it represents a past event, we should not be too quick to assume that this felt quality amounts to a direct awareness of the pastness of events.
The ability to distinguish between memories and imaginings comprises two problems: the source problem, and the process problem (Michaelian 2016, Chapter 9). The source problem is the problem of determining whether information currently being remembered has its origins in experience, testimony, my previous imaginings, or some other source. The process problem is the prior problem of determining whether the cognitive process in which I am currently engaged is one of remembering or imagining. According to the ‘source monitoring’ framework, the source problem is solved by metacognitive processes which ‘infer’ the likely source of a memory on the basis of features of the memory itself—such as the amount and type of perceptual detail it provides, and its fit with background knowledge and other memories (Johnson et al. 1993). The underlying thought is that there are average differences with respect to these features between memories with different sources. Michaelian (2016, pp. 194–198) argues that the process problem is solved in a similar way, by a metacognitive process that infers the likely cognitive process based on features of the representation it outputs, including affective valence and intensity, level of detail, and familiarity.
Whilst these inferences about the source of a representation may sometimes be drawn consciously on the basis of deliberate reflection, in many cases they occur below the level of awareness: ‘heuristic source attributions take place constantly without notice, and are relatively automatic or effortless’ (Johnson and Raye 2000). In the latter case, these ‘inferences’ cannot plausibly be attributed to the agent, but are better understood as ‘occurring at the level of the system’ (Michaelian 2016, p. 165). In these cases, these processes give rise to phenomenal differences between memories and imaginations, in the form of ‘metacognitive feelings’ (Michaelian 2016, p. 196). These feelings may ground a willingness to assign memories episodic epistemic significance that is not to be assigned to imaginings, without the agent being aware of the reasons for their willingness.
Given what we—adult humans—know about the relationship between memory and the past, the presence of metacognitive feelings characteristic of memory gives us a reason to think that the remembered event belongs in the ‘personal past’ (Johnson et al. 1993, p. 21). As a result, we may be inclined to call this feeling a ‘feeling of pastness’. Nevertheless, the feeling is not a direct awareness of the pastness of the event, but the qualitative outcome of a metacognitive monitoring process. It might just as well be designated a feeling of reality, authenticity, epistemic significance or anything else: it is simply a feeling that prompts subjects to assign the memory an epistemic significance not to be assigned to imaginings. In a creature lacking temporal concepts, similar metacognitive feelings could ground a capacity to discriminate memories from imaginings, and to assign epistemic significance to the former but not the latter, without giving rise to a belief that remembered events occurred at some point in the past.
The point, for my purposes, is that if episodic memory and locating remembered events in the past are separable phenomena, then there could be creatures which have episodic memory and which are nevertheless unable to locate remembered events in the past. And I’ve argued that these are separable phenomena. Having episodic memories, in the sense I’ve outlined, does not entail appreciating the pastness of those events, and nor does the capacity to discriminate episodic memories from imaginings. If that’s right, then we ought not to expect (for instance) that creatures with episodic memory will treat remembered events as past in Hoerl’s sense of causally constraining the present, or that they will possess any other kind of temporal understanding.
But, one might reasonably ask, what is it to assign a memory epistemic significance, if it is not to treat it as representing a past event—one that happened at a particular (perhaps unknown) point in the past? And moreover, what good can episodic memory do, if it does not involve locating remembered events in time? It is one thing to say that remembering events and locating them in time are separable phenomena in theory, but quite another to say what cognitive work ‘temporally unanchored’ episodic memories might do. If they could play no useful or adaptive role in a creature’s cognitive economy, it’s unclear why we should take seriously the possibility that any creatures have them. Hoerl and McCormack (2019, p. 4) express this kind of concern, noting that it is unclear how such temporally unanchored event representations could systematically or purposively guide action.
Broadly speaking, I suggest that assigning epistemic significance to a memory means taking it to accurately represent some feature of the world, being inclined to form beliefs about the world on this basis and treat those beliefs as rational constraints on decision making. Standardly, we take episodic memories to have epistemic significance with respect to what happened in the past (Debus 2010). But as I’ll explore in more detail below, there are at least two other ways in which one might take an episodic memory to be epistemically significant, besides by taking it to provide information about the past. First, one might take a memory to accurately represent how things are in the world now. For instance, suppose I have a memory in which my path is blocked by a fallen tree. Even if I do not recognise that this memory represents a past event, I might take it to have epistemic significance with respect to how the world is now: the path is blocked by a fallen tree. Second, one might take a memory to provide information about kinds of events, indicating what tends to happen in certain circumstances. For instance, suppose I have a memory of being bitten by the neighbour’s dog in her yard. Again, without recognising that this memory represents a past event, I might take it to have epistemic significance with respect to the sort of event that’s likely to occur if I go into the neighbour’s yard. Taking episodic memories to have epistemic significance in either of these senses provides for several roles episodic memories might adaptively play in the cognitive economies of creatures lacking any temporal concepts.
First, as Hoerl and McCormack (2019) argue, creatures which do not represent time may nevertheless have what they call a ‘temporal updating system’—that is, a system for keeping track of the current state of the world. One way to do this would be to have a single map-like representation of one’s environment, and update it as one goes about the world to reflect the arrangement of objects one finds. But this is not the only way to keep track of the state of things. One might also store an episodic memory relating to one’s most recent experience at various places and consult this as a record of how things are arranged in the world. So, for instance, suppose I am wondering where my keys are, and a recent memory occurs to me in which my keys have fallen behind a piece of furniture. Even if I lack a concept of the past, I might take this memory to provide information about where the keys are now, which might prompt me to look for them behind the furniture. A creature who used episodic memories only in this way—as a source of information about how things are—would have no need for locating remembered events in time.
One might object that using episodic memories as part of a temporal updating system in this way could not possibly be adaptive.Footnote 7 If subjects do not believe that the events being remembered in fact occurred, it would be irrational for them to use these memories to inform their model of the present state of the world. But whether it is rational for subjects to form beliefs in this way is a distinct question from whether it is adaptive. It would be maladaptive if subjects were disposed to form beliefs on the basis of events which did not happen but were only imagined—since this would tend to result in their having false beliefs about the world. As noted above, however, metacognitive source monitoring processes enable subjects to discriminate between memories and imaginings, even without access to what grounds this discrimination. Sufficiently sensitive source monitoring mechanisms could ensure that an agent reliably forms beliefs on the basis of memories and not on the basis of imaginings, avoiding the maladaptive consequences of the latter, regardless of whether the agent has any beliefs about the temporal status of remembered events.
Second, I’ve argued previously (Boyle 2019a) that storing episodic memories of events increases opportunities for explicit semantic learning—something which may be helpful in situations where it is not obvious what the ‘learning points’ are. Sometimes we are confronted with events which are difficult to interpret, meaning that we can’t at the time draw out any useful information about how to anticipate or respond to these situations. The capacity to store detailed memories of events enables us to revisit them later on, reinterpreting them in the light of more recently acquired knowledge, and extracting relevant information. Again, being able to locate remembered events in time is not important for this purpose. One need not construe the remembered event as something which happened in the past—one might simply view it as an epistemically significant representation of a certain kind of event.Footnote 8
For instance, suppose I am a young chimpanzee learning to fish for termites, and I notice that one of my conspecifics is having much better luck than me. But let’s suppose that I cannot work out what the relevant difference is between me and my conspecific. If I lack any understanding of time, but retain a memory of the event, I might treat it as representative of a certain kind of thing that happens: my conspecific getting lots of termites, using a certain kind of tool, on a certain kind of day. On a later occasion when this or another conspecific is harvesting more termites than me, I might revisit this memory. The commonalities between the current situation and the kind of event I remember might suggest something: perhaps in both cases, my conspecific uses a tool modified with a ‘brush’ tip, whilst I use an unmodified plant stem. This might prompt me to try this technique, and to learn that the brush tool is more effective.Footnote 9 As before, for this use of episodic memories to be adaptive, it is not necessary that I construe remembered events as located at some point in the past, so long as the representations I use in this way are in fact of events located at some point in the past—that is, so long as I reliably use memories in this way, and not mere imaginings. Once again, this discrimination between memories and imaginings can be achieved through source monitoring processes which do not require agent-level judgments about the location of events in time.
Third, episodic memories also seem to play a role in supporting more implicit semantic learning. There’s good evidence in humans that episodic memory plays a role in facilitating the rapid acquisition of semantic information. As noted above, individuals with episodic amnesia—both developmental and adult-onset—are impaired when it comes to the acquisition of semantic information. One explanation of this is that information is initially encoded in episodic memory and then ‘replayed’ for the benefit of semantic learning mechanisms, which can gradually extract information from them. Without episodic memory, many more ‘real’ exposures to information are required. In this way, episodic and semantic memory act as ‘complementary learning systems’ (McClelland et al. 1995). Again, it does not seem important for episodic memory to play this role that subjects be able to locate remembered events in time: treating these memories as epistemically significant representations of events of certain kinds is sufficient. Of course, for this process to be adaptive, semantic memory must reliably extract information from memories of events that did in fact occur, and not from mere imaginings. But, again, the subject need not be capable of temporal thought for this discrimination between memories and imaginings to be achieved.
The above considerations all concern episodic memory’s relationship to locating remembered events in the past. This leaves open the relationship between episodically remembering and having a realist conception of time. Of course, if a creature did not even locate remembered events in the past, it’s unlikely that she would possess a realist conception of time. But suppose that a creature does locate events in the past, in Hoerl’s sense—that is, she treats certain events as being irrevocable, and as causally constraining the present. Should we thereby expect her to have a realist conception of time—that is, to represent time as a domain in which all points are temporally related to all other points, and which exists independently of the events occupying it?
There seems little reason to think so. First, to represent something as past, in this sense, is to represent it as something which did happen. It is unclear how having such a representation would give rise to a judgment to the effect that something else might have happened at that time instead, and thereby to a conception of time as event-independent. Second, to represent something as past in this sense is at most to represent its temporal relationship to the present: because it has happened, it makes an irrevocable difference to how things are now. But this is to say nothing about the temporal relationships it (or the time it occupies) stands into other times—and so it falls short of conceiving of time as a continuous domain. Teresa McCormack and Christoph Hoerl (2017) propose that children may develop this minimal understanding of the difference between past and future events between 2 and 3 years old. But this capacity to discriminate those situations which can still be altered from those which, having happened, cannot be altered differs considerably from having ‘one unified model of the world within which time itself is represented’ (Hoerl and McCormack 2019, p. 11).
Locating a remembered event in the past, even in this minimal sense, increases the cognitive work that one’s memory of that event can do. For one thing, recognising that an event has happened and cannot be undone might lead one to realise that there is no point dwelling on it (McCormack and Hoerl 2017, p. 310). More concretely, if one treats the remembered event as constraining the present, one might draw certain inferences about what must be true now, or what I ought to do now, given that the event occurred. For instance, remembering an occasion on which I saw a sapling in a certain spot, I might infer that there is likely to be a mature tree there now. Similarly, remembering an interaction in which I was unduly harsh toward someone might lead me to adopt a more conciliatory attitude when I meet them now. But treating events as past in this sense does not provide for a sense of the temporal relationships between remembered events, which limits the rational uses to which memories can be put. For instance, suppose that I remember seeing Tina in the garden, and that I also have a distinct memory of finding a book in the garden. If I represent these events as past but can’t conceive of any temporal relations between them, certain inferences—such as that Tina left her book in the garden—will be unavailable to me.
On the view I’ve proposed, episodic memory is memory for events, not memory for the times they occupy: one can remember events without representing the times they occupy, and without representing those times as event-independent. Episodic memories which fail to locate events in the past or in event-independent time may nevertheless play a number of productive roles in a creature’s cognitive economy. So, we should take seriously the possibility that some creatures—perhaps nonhuman animals and young children—have episodic memories, and yet lack any kind of competence with temporal concepts. If this is right, then the straightforward evidential link I considered above does not obtain: we should not infer from a lack of evidence for temporal cognition in a creature that the creature lacks episodic memory.
In this section, I have assumed a relatively inclusive picture of episodic memory, according to which episodic memories are those memories involving a single spatially organised construction of a scene. As I noted above, there exist a number of more restrictive accounts of episodic memory, which view episodic memories as a proper subset of the memories I have been discussing, characterised by the possession of further distinguishing features. So, one might worry that perhaps when philosophers have found it plausible to claim that episodic memory furnishes us with our concepts of the past or of time, they had one of these less inclusive conceptions of episodic memory in mind.Footnote 10
Since it is difficult to rule this out, my argument can be viewed as limited in scope. I’ve argued that there are good reasons to treat episodic memories as memories involving spatially organised constructions of scenes; certainly, this idea is at the heart of any plausible account of episodic memory, even where it is taken to have other distinguishing features. I’ve argued that this kind of memory does not provide for an understanding of the past: remembering events does not entail representing time. Of course, this does not rule out that on some narrower construal of episodic memory, it does furnish us with a concept of the past, in virtue of other features by which it is characterised. Nevertheless, I think there are at least two reasons for scepticism.
First, the prima facie reason for thinking that episodic memory furnishes us with temporal understanding is that it provides for direct awareness of the pastness of events. But I’ve argued that whilst episodic memory may provide for direct awareness of past events, there is no reason to think that it provides for direct awareness of their pastness. In particular, the most plausible candidate feature of episodic memory for providing a direct awareness of pastness is the so-called ‘feeling of pastness’. But, I’ve argued, this is not a direct awareness of the pastness of events, but the felt outcome of a metacognitive process enabling subjects to discriminate memories from other cognitive phenomena. Since there is nothing intrinsically ‘past-ish’ about this feeling, it is difficult to see how it could furnish a creature with temporal concepts. Rather, I’ve suggested, we may call it a feeling of pastness because we possess temporal concepts. This undercuts a central motivation for thinking that episodic memory furnishes us with temporal understanding.
Second, one might suspect that on at least some narrower construals of episodic memory, it depends developmentally on the possession of temporal concepts—and if so, it could not be true that it furnishes us with them. For instance, take Mahr and Csibra’s construal of episodic memories as those event memories agents explicitly take themselves to remember. Since understanding what it is to remember something entails knowing what it is for something to be in the past, remembering in this sense is clearly sufficient for temporal understanding. But this tells us nothing about the development of temporal understanding, unless we have an account of our capacity to judge that we remember—and one might reasonably suspect that this turns on the acquisition of temporal concepts. Similarly, take Keven’s account, according to which episodic memories are characterised by the possession of causal, temporal and teleological structure, and not merely spatial structure. Keven argues that in humans, the capacity for narrative storytelling is key to the development of this more sophisticated form of memory—and one might think that developing the capacity for narrative storytelling involves acquiring at least some facility with temporal concepts. If that’s right, then episodic memory in Keven’s sense is unlikely to be what furnishes us with temporal concepts. More generally, making the case that episodic memory (on some narrower construal) furnishes us with temporal concepts requires giving an account of how episodic memory (in this narrower sense) might develop in the absence of temporal understanding. But there is at least some reason to suspect that matters are more complicated than this: that more sophisticated forms of episodic memory are developmentally entangled with an emerging understanding of time.
Of course, it may be that even if episodic memory does not furnish us with a concept of the past on these narrower construals, it nevertheless stands in interesting evidential relationships to temporal cognition. For instance, clearly, if a creature has episodic memory in Mahr and Csibra’s sense, then it must have some understanding of what it is for an event to be past; this much is true by definition. But these evidential links are unlikely to be entirely straightforward. We could not assume, for instance, that a creature possessing a concept of the past would have episodic memory in Mahr and Csibra’s sense since, aside from anything else, this also requires a capacity for explicit metacognitive judgment. Similarly, there is no obvious reason to expect that a creature possessing episodic memory in Mahr and Csibra’s sense would have a realist conception of time, or any concept of the future. So, whilst evidential connections may exist between narrower construals of episodic memory and temporal cognition, determining the precise nature of those connections requires careful attention to the details of the relevant construal of episodic memory, and to the varieties of temporal cognition.