MAUREEN ECKERT
Fatalists regard the future like the past. Time travelers regard the past like the future. This mirroring of the fatalist and time traveler suggests that there is some kind of common ground between them—but what is it? According to the fatalist, there is nothing now we can do to influence future events. Meanwhile, the time traveler can do things to influence the past. We may prefer the time traveler to the fatalist—being a Time Lord promises considerably more adventure than necessarily having to do everything that one does. Yet, both positions seem counterintuitive about whatever it is we can and cannot do, past and future. In the debate spurred by Richard Taylor’s fatalism argument, the connection between fatalism and time travel begins to take shape in Taylor’s response to the “Ability Criticism.” The first section of this paper reviews this development of the issue. In the second section, we examine David Lewis’s analysis and dissolution of the Grandfather Paradox, which further clarifies the connection. The third section of this paper examines how David Foster Wallace’s critical response to Taylor’s fatalist argument avoids the pitfalls of the earlier Ability Criticism. The semantic system he develops, System J, provides precision to Lewis’s more general account of how a time traveler can act in the past without risking contradiction. We will see, in the final section, that the metaphysical commitments of System J would shut down actual time travel along with fatalism. Their initial mirroring turns on a common conceptual flaw.
FATALISM AND TIME TRAVEL ON THE CHEAP: THE ABILITY CRITICISM
In his “Note on Fatalism,” Richard Taylor assesses the “Ability Criticism,” an attack against the fifth premise of his fatalist argument. This premise reads: “Fifth, we presuppose that no agent can perform any given act if there is lacking, at the same or any other time, some condition necessary for the occurrence of that act.”1 The group of critics concerned, including Aune, Saunders, and Abelson, claim that an agent can, in fact, perform actions in the absence of a condition necessary for it to be accomplished. This is the case when an agent’s abilities are concerned—hence the Ability Criticism. I can swim, for example, if it is the case I have learned how to do so and practiced it to proficiency—I am able to swim. I may be lacking some condition necessary to swim, e.g., being in a filled swimming pool, but it is true that “I can swim” in this sense.
According to Taylor, the Ability Criticism conflates three distinct notions: (1) what is within one’s power to do given external circumstances, (2) what is possible for one to do, and (3) what is within one’s ability to do given internal circumstances. This conflation, for Taylor, is significant because his argument is unaffected by (3), the individual “ability/skills” rendering. Even if I possess the ability to swim, it remains impossible to swim without necessary conditions being met (e.g., a present body of water in which to swim), and is it not within my power to exercise my ability in the absence of a necessary condition. Moreover, if the “can” of Taylor’s fifth premise is understood as meaning “ability,” there is a hidden cost. Reducing the notions of “possibility” and “what is within one’s power” to “ability” for the sake of solving fatalism entails that abilities would then override possibility and doing whatever is within one’s power generally. If the ability to swim, even lacking necessary conditions, liberates us from fatalism about future contingent events, it simultaneously allows us to change the past—what is possible and what is in our power to do no longer constrain our abilities. Contingent events that have happened in the past could be undone by what we can do—as abilities. Time travel comes much too cheaply if the ability criticism is taken seriously. Taylor states:
Remarks upon what one may or may not have the ability to do, in the usual skill sense of ability, have no relevance to this problem at all. Not one of my critics has seen this. Nor have they seen that the very refutations they give of my fatalism about the future would work just as well to prove that we should not be fatalists about the past. I described a fatalist, however, simply as a man who looks upon the future the way we all look upon the past, so far as concerns what it is and what it is not within his power to do. If anyone wanted to show that we should not be fatalists about the past, that it is to some extent now up to us what happens yesterday, and so on, he could find all his arguments in the remarks of my critics, needing only to change a few tenses.2
Taylor notes that we are all fatalists about the past (the fatalist merely treats the future as we all consider the past).3 The conflation of possibility, what is within one’s power to do, and abilities leads to an unacceptable result—the ability to change the past by way of abilities. Disambiguating the senses of “can” in Taylor’s fifth premise permits the fatalist argument to go through. In this way, Taylor dispenses with the Ability Criticism.
Taylor’s response to the Ability Criticism nevertheless leaves some lingering concerns. He notes that there are three distinct senses of “can” that his critics conflate: (1) what is within one’s power to do, (2) what is possible for one to do, and (3) what is within one’s ability to do. Disambiguating the sense of “can” in the premise so that it does not regard an agent’s abilities and skill sets (3) still leaves open what is going on with the distinctions he makes in (1) and (2). What is possible logically is much, much broader than what happens to be in one’s power to do. Local, physical circumstances are relevant to what is or is not within one’s power, as should be expected since it is the status of future contingent statements under consideration and not all possibilities. What is in one’s power to do is a subclass of what is possible, but one must avoid conflating (1) and (2), as cases of what is possible (1) far outstrip whatever is in one’s power to do (2). Thus, there remains some leverage for critically responding to premise five of Taylor’s fatalist argument. David Foster Wallace exploits this remaining ambiguity in his attack on the fatalist argument, disambiguating these two remaining senses of “can” through distinguishing between physical possibility and what he terms “situational physical possibility.” More will be said on Wallace’s insight and metaphysical solution in the section “Wallace’s System J,” below.
Additionally, Taylor’s response to the Ability Criticism relies on an intuitive notion of the past that can be challenged. We may all be fatalists about the past—except when we aren’t. Science-fiction writers have not viewed the past fatalistically, as fans of Doctor Who might note. Contemporary physicists have seriously debated the theoretical possibility of time travel. Most importantly for our purposes, anyone arguing philosophically for the possibility of time travel, especially time travel into the past, must disambiguate (1) what is within one’s power to do from (2) what is possible for one to do when constructing an account. As Taylor diagnoses the problem, conflating individual ability with what is possible for one to do and with what is in one’s power to do provides a cheap and unconvincing route to time travel. One’s abilities do not allow anyone to change the past. The time-traveling “ability” has to be more than merely a skill, as Taylor claims. David Lewis’s assessment of the Grandfather Paradox in his argument for the possibility of time travel illustrates this condition.
TIME TRAVEL AND FATALISM ON THE CHEAP: DAVID LEWIS ON THE GRANDFATHER PARADOX
If a time traveler, Sarah, were to travel back in time two generations, can she kill her own grandfather? It would seem that, on the one hand, if she has successfully traveled back in time, causally interacting with the world at that time, and she is in the right location with a weapon at hand, there is nothing at that time that would prevent her from killing her grandfather. On the other hand, if, at that time, she were able to kill her own grandfather, she would then eliminate a necessary condition for her existence—there would be no future Sarah that can travel back in time to commit the act in question. The question of whether the time traveler Sarah can kill her grandfather appears to give rise to a contradiction. Time-traveling Sarah both can and cannot kill her grandfather. This “Grandfather Paradox” presents an obstacle to the notion that time travel to the past is possible. In “The Paradoxes of Time Travel,” David Lewis attempts to dissolve this paradox with the intention of showing that it is possible.4 Crucial in his analysis is an ambiguity also noted by Taylor: there are two senses of what a time traveler can do.
For Lewis, a time traveler arriving back in time before her own birth, able to interact causally with the environment and to be in the right place at the right moment with the right weapon, “has what it takes” to kill her own grandfather.5 Lewis calls this way of tracking the time traveler’s local actions “personal time.” Personal time essentially moves with the time traveler such that she experiences her “now” wherever she happens to be in terms of the line of “objective time.” Traveling back in time, she is objectively in the past, but it is her personal-time present. A Lewisian time traveler’s “having what it takes” at the local, personal level of time corresponds to what Taylor calls having something “within one’s power to do.” With these phrases, both philosophers refer to the relevant contextual, situational details necessary to carry out an action. It is within Sarah’s power to kill her grandfather in her personal time. But is it possible? Like Taylor, Lewis also distinguishes a broader kind of possibility from the contextual, situational sense of being able to do something. The broader range of facts about a time traveler—one that is inclusive of the whole chain of events that leads up to the time traveler’s trip back to the past—excludes the possibility of killing one’s own grandfather. These two ways of conceiving what a time traveler can do dissolves the paradox. He states: “You can reasonably choose the narrower delineation, and say that he can; or the wider delineation, and say that he can’t. But choose. What you mustn’t do is waver, say in the same breath that he both can and can’t, and then claim that this contradiction proves that time travel is impossible.”6
Lewis’s diagnosis of this equivocation in what we mean by “can” in the time-traveler case applies to fatalism. For Lewis, the sleight of meaning rests in taking irrelevant facts as relevant facts. In other words, the fatalist argues it is necessary that we do what we do (and don’t do what we can’t do) by claiming that irrelevant facts about the future are relevant facts about the past. The time traveler has it within her power to kill her grandfather when narrowly and contextually considered. This maps to an ordinary sense of what we mean when we say we can do something. Shift the context such that we include all of the future events up through the time traveler’s trip into the past as part of the context, and she cannot. She is, apparently, “fated” not to be able to do so. The Grandfather Paradox disguises this same shift in context operating in the fatalist’s perspective. “We are unlikely to be fooled by the fatalist’s methods of disguise in this case, or other ordinary cases,” Lewis states. “But in cases of time travel, precognition, or the like, we’re on less familiar ground, so it may take less of a disguise to fool us.”7 The fatalist exploits the context of objective time in order to determine (for once and for all) what we can and cannot do at the local level of personal time.
Lewis’s dissolution of the Grandfather Paradox might leave some residual dissatisfaction. Personal and objective times are nevertheless in tension. One might suspect that a time traveler who can, in the narrow situational sense, kill her own grandfather is up to something that isn’t merely logically off (contradictory) and certainly ethically off but also “metaphysically off.” This latter oddness may be hard to tease out, although it seems clear that the time-traveling grandfather killer can very radically change the past, thus altering the physical chain of events in some real sense, if she really can kill her grandfather. The strongest way to address this radical alteration of the physical world is through the notion of branching time. According to Lewis, in such a scenario we find branches of time at which the grandfather is killed, others where he is not, but never one in which he both is and is not killed.8 We still have a consistent story, one in which the time traveler appears and kills her grandfather in one branch while in other branches of time she does not. The consistency of each story depends upon tracking the time traveler’s personal time in any given temporal branching. Why can’t a time traveler succeed in preventing her own birth? For Lewis, insofar as we track this time traveler’s (admittedly) unusual story along a branch of time, there is nothing to block it merely because it is so unusual. There is no contradictory branch, but this does not mean that things are quite normal along some branches of time.
The highly unusual sort of story seems to entail an abrogation of the situational physical causal chain of events that brought the time traveler into existence. Time-traveler Sarah can kill her grandfather in 1938 when she has traveled back to 1938 insofar as all the right circumstances are in place. We can grant this to Lewis. Yet the right circumstances were also in place to cause her father to be born, etc., etc. Every event in Sarah’s history in objective time was once a moment of experience in personal time. How could one action at the end of this sequence of physical events have the “metaphysical juice” of existential erasure? Could a time traveler actually be going back to that time at which her grandfather lived—backtracking in metaphysically real time? Is this really possible? This is another way of asking whether or not Lewis has fully explored all that it means for time travel to be possible by establishing the personal and objective distinctions in time. Fatalism may be a cheap trick, as Lewis holds, yet time travel cannot be so expensive that a single event in personal time can, in principle, erase those that constituted it in objective time. Lewis seems to have potentially reduplicated a version of the Ability Criticism in attempting to defend a way to hold that time travel is possible. David Foster Wallace’s account of situational physical modality and the semantics he provides for it, System J, prove useful for exploring Lewis’s account of the shift of context driving the Grandfather Paradox while pushing further into matters of modality.
WALLACE’S SYSTEM J
In “Richard Taylor’s ‘Fatalism’ and the Semantics of Physical Modality,” David Foster Wallace further sharpens and elucidates the distinctions with respect to the senses of “can” that Taylor had made in his assessment of the Ability Criticism. Where Taylor distinguished between (logical) possibility, ability, and an action being “within one’s power,” Wallace distinguishes alethic (logical), physical modality and then, in a crucial move, also distinguishes a type of physical modality, which he terms “situational physical modality” (SPM). This latter modality is so crucial because Wallace determines that it is the level of modality that is at stake when considering the status of future contingent statements. Considering the classic example employed by Taylor of the admiral giving an order (O) today that causes a sea battle (B) tomorrow, Wallace observes:
The kinds of modalities we are concerned with in an analysis of the Taylor problem must be regarded as situational physical modalities. The alleged entailment-relation between O and B is not logical, and there is no contradiction in (O ∧ ~B). And O does not physically ensure B simpliciter; rather it does so because of, in Taylor’s own words, “the totality of other conditions prevailing,” and because of the stipulated causal efficacy of O with respect to B in the situation characterized.9
The extent to which we might be willing to accept Wallace’s critique of Taylor’s fatalist argument and the semantic system he proposes hinges on whether we accept this distinction in types of physical modalities—“a difference,” as he states, “between what is just physically possible in general and what is physically possible for a given agent to do in a given set of circumstances.”10 Physical possibility simpliciter concerns the laws of nature; situational physical modality “concerns the modal character of events, actions, and states of affairs, taking into account not only general and unchanging physical laws, but also the situations and circumstances that can affect what is possible and necessary at certain places at certain times.”11 Importantly, SPM influences any reading of premise five of Taylor’s fatalist argument (we presuppose that no agent can perform any given act if there is lacking, at the same or any other time, some condition necessary for the occurrence of that act). If Taylor’s fatalist conclusion (all actions and inactions are necessary) involves a different sort of modality than that operating in premise five, his argument is rendered invalid. Wallace takes inspiration from the critical literature in developing his position, particularly the Ability Criticism that Taylor had addressed. However, Wallace is well aware that he needs to steer clear of ideas regarding internal skills/ability and must address the external circumstantial constraints that premise five concerns.12 Lewis’s notion that a time traveler can act in personal time with respect to a narrower context of relevant facts (hence can kill her grandfather) amounts to Wallace’s understanding of SPM. According to Lewis, the fatalist ushers in irrelevant future facts through shifting context from SPM to a different, broader range of facts (those perceived from the standpoint of objective time). Wallace shows how this problematic shift in context operates semantically.
A key piece of Wallace’s semantic machinery, System J, is the application of temporal indexes to situational physical modal statements governed by the (novel) SPM operators he introduces. Situations are joined in “mother-and-daughter” relations that compose causal paths. Mother situations give rise to a (limited) set of possible daughter situations. Daughter situations become, in turn, mothers of another temporally distinct set of daughters, and so on. This model permits a fine-grained tracking of situational physical modalities and, ultimately, their relationships over time, preventing the crucial scope errors that the fatalist argument trades upon. He describes this scope precision:
Remember that situational physical modalities (the truth-values of physical-modal propositions) vary with time and with the physical situations that obtain at different times. Therefore the evaluation of any physical modal statement is going to be an evaluation relative to a time and to the physical situation obtaining at that time. Thus we may say that any physical-modal operator in a really well-formed physical-modal formula should appear within the scope of, and be evaluated in the context designated by, a tense-operator or time-marker specifying some time-situation index. When no tense-/time-operator appears to govern a physical-modal operator in a well-formed proposition, the relevant time-and-situation index of evaluation should be understood as an implicit “now.”13
So, to help clarify, Wallace’s system allows us to see that given the absence of a sea battle (~B) today (now), we can conclude that it was not possible that the admiral gave his order yesterday, but we are not entitled to conclude that yesterday the admiral could not give the order. The possibility or impossibility of his giving the order depends on its mother conditions the day before yesterday.
With this disambiguation, however, we also find the most radical feature of System J, a feature Wallace embraces and defends—it allows for no alternative presents in the context of a given actual present. Two truths are compossible in System J:
(c) Yesterday it was possible for the admiral to issue order O.
and
(d) It is not possible today that the admiral did issue order O yesterday.14
Is this a bug or a feature of his system? Has Wallace inadvertently built a case for fatalism through constructing the machinery to dismantle it? Wallace believes it is a feature—and that System J does not, in the end, justify fatalism. Our unease about how alternative presents are treated in System J is a residual effect of conflating logical and physical possibility. Alternative pasts and alternative futures that are physically compatible with an actual present are permitted in System J, but nevertheless “there are here really no ‘alternative presents,’ no ‘worlds’ contemporary with the actual world now, and with at least one feature different from the features of the situation that obtains in the actual world now, which are nevertheless physically compatible with the situation that obtains in the actual world now.”15 Wallace emphasizes that his conception of SPM differs from Kripke/Montague models of modality, which are not contextually and temporally sensitive. His diagnosis is compelling:
These philosophers understand possibility as a synchronic relation between cotemporal, ideally existing worlds. They think of “alternative presents” in terms of an infinitely long row of alternative logically possible worlds intersecting a horizontal time-axis at “now.” They think of evaluating “present possibilities” in terms of ranging along that row of simultaneous worlds, rather as one might scan a shopping list. When they feel they are being denied any alternative presents, these philosophers may be inclined to see their row of worlds suddenly collapsing into a single constraining actuality-turned-necessity.16
Since System J models only physical situational possibility contextually, it does not deny that there are alternative logically possible presents. For Wallace, System J accurately reflects common sense regarding the actual physical present: “What is actual now is, quite obviously, physically compatible with what was actual a few moments ago and gave rise to what is actual now.”17 Moreover, given this fixity of actual physical presents once they are actualized, System J preserves fatalism about the past—a result that Taylor himself would find amenable.
Returning to Lewis’s treatment of the Grandfather Paradox with System J at hand, the activities of a time traveler can be reexamined. It starts to look as though time travel itself is a kind of thought experiment that is so much the worse off if, as Lewis insists, we decide that the time traveler can kill her grandfather (or even herself at an earlier age), in what Lewis finds to be the narrow sense of personal time regarding situational, local facts. Under System J, there simply is no way a time traveler can actually and physically return to a past moment in personal time. There is nothing in System J that blocks the conceivability of this. Yet, to conceive of this possibility, for Wallace, cannot be confused with what is physically and actually possible. Returning again to Lewis’s diagnosis, if we decide to consider the time traveler given the broadest range of relevant facts via objective time, the time traveler cannot kill her own grandfather. The logical contradiction involved operates in this context. Our conceptions of time travel—the stories we create—have coherence because it is easy enough to focus on the personal time of a time traveler to spin a familiar narrative about what characters can do. The fascinating loops in time that emerge in such narratives gain effectiveness from the logical contradictions that accrue to the time traveler and whatever she does in objective time.
It is difficult to say whether or not Wallace would consider of the fictionalization of time travel to the past resulting from his position on fatalism to be a bug or a feature of his system. On the one hand, strongly preserving free will through solving Taylor’s fatalist problem motivated Wallace’s construction of System J. On the other hand, Wallace’s construction of a metaphysical argument aimed at showing that Taylor’s semantic argument cannot lead to metaphysical conclusions comes at a metaphysical price. Present physical actuality, privileged by System J, is sharply distinguished from logical possibility and, as we have seen in the case of time travel, conceivability. An author of fiction might hesitate to sever fictional realms from the actual physical world so cleanly and decisively. Then again, perhaps not. The elegance involved in dismantling two mirrored counterintuitive positions about what we can and cannot do in the future and the past could prove the most irresistible feature of System J.
NOTES
1. Richard Taylor, “Fatalism,” Philosophical Review 71, no. 1 (January 1962): 58. Emphasis mine. Also in David Foster Wallace: Fate, Time, and Language—An Essay on Free Will, ed. S. Cahn and M. Eckert (New York: Columbia University Press, 2010), 43.
2. Richard Taylor, “A Note on Fatalism,” Philosophical Review 72, no. 4 (October 1963): 99. Also in David Foster Wallace: Fate, Time, and Language—An Essay on Free Will, ed. S. Cahn and M. Eckert (New York: Columbia University Press, 2010), 87–88.
3. Taylor, “Fatalism,” 56; also in David Foster Wallace: Fate, Time, and Language, 41–42.
4. David Lewis, “The Paradoxes of Time Travel,” American Philosophical Quarterly (April 1976): 145–152.
9. David Foster Wallace, “Richard Taylor’s ‘Fatalism’ and the Semantics of Physical Modality,” in Fate, Time, and Language: An Essay on Free Will, by David Foster Wallace, ed. S. Cahn and M. Eckert (New York: Columbia University Press, 2010), 150.
12. Ibid., 152. Wallace covers Taylor’s response to Bruce Aune and the Ability Criticism in this section of his thesis. He states here: “Just what Taylor means by ‘circumstantial constraint’ may become clearer in the context of a related objection to presupposition 5 advanced by Bruce Aune. How proper is it to say that I ‘cannot,’ have not the ability to, perform an act if I am absent a condition necessary for that act? For instance, it is often a necessary condition of my doing p that I try to do p, but do we say that in those cases when I do not try to do p it follows that I lack the power or ability to do p? In order for me to play tennis, it is necessary that I have a tennis racket, but does the absence of a racket mean that I lack the ability to play tennis? Quite clearly not. But Taylor and others have reasonably replied that the ‘cannot’ of the Taylor problem is a ‘cannot’ of circumstances, not really of ability, that it represents an exterior, not an interior, limitation.”