Volume 14, No 2, Fall 2019 ISSN 1932-1066

Jaspers on Death

Kiki Berk

Southern New Hampshire University

Abstract: This essay offers an analytic engagement with Karl Jaspers' philosophy of death. One of the central ideas in Jaspers' philosophy of death is that the way in which one confronts one's mortality and responds to the existential Angst it generates has profound existential significance. Particularly, Jaspers holds that one can achieve genuine authenticity only by facing up to one's mortality and by confronting it with courage. This essay situates Jaspers' philosophy of death within the current analytic philosophy of death and presents Jaspers' answers to its main questions including whether death is bad, whether one should fear death, whether death can be survived, and whether immortality is desirable.

Keywords: Jaspers, Karl; death; mortality; Angst; authenticity; philosophy of death; analytic existentialism.


Death has become a popular topic in contemporary analytic philosophy. Analytic existentialism addresses questions such as what happens at the time of death, whether death is bad for the one who dies, whether we ought to fear death, and whether it is rational to want to live forever. Unfortunately, this literature rarely engages the work of traditional existentialist philosophers such as Jean-Paul Sartre, Albert Camus, Simone de Beauvoir, Martin Heidegger, and Karl Jaspers. The main reason for this lack of engagement is that analytic philosophers perceive the writings of these Continental philosophers as being obscure. This essay is an attempt to remedy this lack of engagement by analyzing from an analytic perspective Jaspers' philosophy of death, as set forth in the second volume of his Philosophy,1 and by connecting it to corresponding debates in analytic existentialism. Drawing upon these connections, I attempt to enrich the debate in analytic existentialism by introducing Jaspers' ideas on death.

The Existential Significance of Death
Viewed Analytically

In a nutshell, Jaspers' philosophy of death can be understood as follows: What makes death existentially significant is not the fact that one must die but rather the confrontation with mortality that it generates. This confrontation gives rise to existential Angst, and it is precisely one's response to such Angst that determines whether one can come to realize one's full potential. Simple avoidance, which can take on a variety of different forms, is the usual response to existential Angst. Nonetheless, avoiding such Angst comes at a high price, since it is only by facing up to death with courage that one is able to live authentically. Death, then, is a test, and facing up to and accepting one's own mortality provides an opportunity to become true to oneself and to others.

In her analysis of Jaspers' concept of death, Filiz Peach observes that there is a sense in which death is existentially significant and another sense in which it is not.2 For the objective self, death is not existentially significant. For the sake of clarity, "objective self" is here used with reference to Jaspers' notion of Dasein, or "existence," or "mere existence," or "empirical existence," according to which the self is understood as a concrete physical and sociological human being. Nonetheless, the objective self's finitude gives rise to what Jaspers calls "boundary situations." Peach describes these as "unclear and oppressive, situations that one cannot modify" (DDE 42). As a boundary situation, death brings about existential significance for the existential self. I shall use "existential self" when referring to Jaspers' notion of Existenz, or "Self-Being," or, in Peach's words, the "ineffable inner core of the individual," which is "the non-empirical and non-objective dimension of the human being" (DDE 35). Peach points out that "Jaspers often refers to Existenz as 'possible Existenz'" (DDE 36), thereby making a distinction between a momentary experience of Existenz and one's progressive achievement of authentic selfhood.

For the objective self, death is an objective and general fact. All humans are going to die, and death is the end of one's phenomenal, practical existence in the world. Finitude is a fundamental feature of the objective self: every single human person is a finite biological being with a limited lifespan. When merely taken as being an objective limit to one's existence, death is not existentially significant. After all, the objective self arguably does not experience its own death and, instead, experiences itself as being timeless. Sigmund Freud goes so far as to claim:

We cannot, indeed, imagine our own death; whenever we try to do so we find that we survive ourselves as spectators. The school of psychoanalysis could thus assert that at bottom no one believes in his own death, which amounts to saying: in the unconscious every one of us is convinced of his immortality.3

In this account, death is simply the point in time when the curtain drops, and experience stops. This is reminiscent of Jean-Paul Sartre's view when he describes death as being "the final boundary of human life...a door opening upon the nothingness of human-reality."4 When seen in this way, death is outside of human experience and, as such, does not have any existential or subjective significance. Sartre writes to this effect: "Since death is always beyond my subjectivity, there is no place for it in my subjectivity" (BN 548). In Being and Nothingness, Sartre argues strongly (though not explicitly) against Martin Heidegger's view that death is existentially significant. However, for Jaspers, there is more to the story, and, as is shown below, his view is ultimately much closer to Heidegger's than it is to Sartre's.

For Jaspers, a human person does not just exist as an objective self, but is also potentially an existential self. Being opposed to the objective self, the existential self is infinite but aware of the objective self's finitude. When confronted with death (one's own or somebody else's), a boundary situation can occur. Occasionally translated as "limit situations," or "ultimate situations," boundary situations play an important role in Jaspers' early philosophy and are best understood as existential crises. For example, Ronny Miron and Chris Thornhill explain:

Limit situations are moments, usually accompanied by experiences of dread, guilt or acute anxiety, in which the human mind confronts the restrictions and pathological narrowness of its existing forms, and allows itself to abandon the securities of its limitedness, and so to enter new realm of self-consciousness.5

Expanding upon Adolph Lichtigfeld's interpretation that a boundary situation "succeeds in awakening the individual self to its existential content," Peach adds that boundary situations "can also be seen as the crises in human existence in which they appear as internal contradictions" (DDE 42). I think that the idea of an existential crisis maps quite well onto Jaspers' concept of a boundary situation.

Jaspers distinguishes four specific boundary situations: suffering, guilt, struggle, and death. When being confronted with one's own mortality, and by becoming fully aware of one's own future death, existential Angst manifests itself. The existential significance of this experience, that is, the existential crisis that mortality evokes, consists in the unique opportunity it provides: facing up to it with courage by accepting that each breath taken is one fewer breath to take and, by grasping the illusory permanence of youth and health, can lead to the realization of authenticity and selfhood. These reflections on death make the similarities between Jaspers and Heidegger apparent: Heidegger, too, thinks that being-toward-death enables one to live authentically.

Jaspers does not say much more about how, exactly, one copes with an existential crisis with courage or what it entails to achieve authenticity and selfhood. Nonetheless, Peach offers the following insight:

Jaspers holds that since one cannot escape from death, one should face up to it with dignity, accept it and come to terms with it, instead of living with the fear of it. Facing up to one's own death and integrating it into one's existence may lead to the fullness and richness of the experience of life. [DDE 85]

Avoiding Existential Angst

For Jaspers, the life of a fully realized, authentic existential self is one that is fulfilled and feels at peace. Trained as a psychologist, Jaspers elaborates on the different ways to avoid existential Angst and the inauthentic ways of living that result from it.

How we respond to existential Angst is crucial for Jaspers. But what is existential Angst? From the outset, it is important to distinguish existential Angst from the fear of dying. Unlike fear of dying, existential Angst does not have a concrete object, such as the pain that the process of dying can involve. Existential Angst, rather, is "the horror of not being," in Jaspers' terms (P2 197) or, as Beauvoir expresses it, "the horror of this endless night."6 Peach describes Jaspers' concept of existential Angst as the "indeterminate fear" that "must be understood in terms of one's confrontation with one's own possible non-being" (DDE 79). Existential Angst, then, seems to be the fear of the state of non-existence after one's death has occurred.7 Feelings of loneliness, helplessness, and despair are commonly associated with this state. Facing up to existential Angst gradually changes the focus from youthful illusions of courageous conquest to realistic assessments of the inevitability of the soon-to-come event, regardless of whether or not one tries to avoid it. Jaspers' discussion of the ways of avoiding existential Angst provides great insight into Jaspers' idea as to how one ought not to address mortality.

One way to avoid existential Angst consists in immersing oneself in the objective self. This means that one clings entirely to worldly phenomena and takes them as being endless and absolute instead of being finite, transitory, and insignificant. In other words, the focus is fully on worldly pleasures and activities. "I lose myself in appearance" (P2 196), as Jaspers puts it; and this, he argues leads to a hunger for life, jealousy, pride, ambition, and fear.

Another way to avoid existential Angst is the opposite of the previous one: by trying to ignore the objective self's needs and focusing entirely on the transcendental realm, for example as mystics do. Peach points out that Jaspers believes this approach to be the other extreme for evading existential Angst. She explains that Jaspers

repeatedly claims, possible Existenz has an antinomic relationship with the world: it cannot be separated from it, nor can it be entirely unified with it. In other words, Existenz is in a dialectical relationship between the empirical and the transcendent realm, and the balance between the two must be maintained. [DDE 81]

As should be clear, neither the first nor the second way maintains a balance between the empirical and the transcendental but instead focuses exclusively on one at the expense of the other. It is worth pointing out that Thomas Nagel makes a similar distinction between being fully immersed in life from one's own point of view and assuming a point of view sub specie aeternitatis. He argues, like Jaspers, that it is impossible for humans to give up either one of these viewpoints and that it is uniquely human to be able to take up both of them. Nagel famously claims that the discrepancy between these two points of view is what makes human life absurd. He writes:

We cannot live human lives without energy and attention, nor without making choices which show that we take some things more seriously than others. Yet we have always available a point of view outside the particular form of our lives, from which the seriousness appears gratuitous. These two inescapable viewpoints collide in us, and that is what makes life absurd.8

This realization that human life is absurd can very well give rise to existential Angst, which one might try to resolve by abandoning one of the two points of view. As pointed out earlier, Jaspers does not think that this would be a good option.

A different way to avoid existential Angst is by changing the boundary situation into something different so that it ceases to be a true boundary situation. As Jaspers puts it, this transforms "the meaning of death as a boundary" (P2 196). Jaspers discusses two different ways of doing so: by employing logic or by adopting a belief in an afterlife. These, then, are two additional strategies for avoiding existential Angst.

Employing logic is not to be understood in terms of solving formal logic problems but rather as rational reasoning about death. Without providing an explicit reference to it, Jaspers discusses Epicurus' strategy for alleviating fear of death. Epicurus famously said, "death…is nothing to us, since so long as we exist, death is not with us; but when death comes, then we do not exist."9 His point is that even though fear of death is natural, it is not rational for one will never experience it; and after one's death, there are no experiences at all: neither good nor bad ones. Jaspers thinks that Epicurus' argument, although logically sound, does not do much to overcome existential Angst. It is hard to pinpoint where this argument goes wrong, but nonetheless, Jaspers thinks, it fails to take away the fear of death. For Jaspers, fear of death is not assuaged by these logical thoughts that

seem to look death in the eye, but in effect they make me only more oblivious of its essence. They ignore that there are things to be finished, that I am not through, that I still have to make amends—above all, that time and again I am filled with a sense of being as mere existence, which becomes pointless when I think of an absolute end. [P2 197]

This third strategy is not so much a way we ought not to live, as the previous two strategies are, but rather one that Jaspers considers to be ineffective. Jaspers makes an interesting point here that rational arguments are not always effective when thinking about a topic such as death.

Just like the strategy of logic, the strategy of adopting belief in an afterlife transforms the boundary situation of existential Angst into something else. By upholding the belief in an afterlife, death ceases to be the end of one's existence, and the presumed stage of transformation no longer constitutes a genuine boundary situation: "Death has been conquered at the cost of losing the boundary situation" (P2 198). This approach does get rid of existential Angst but, like the first strategy, also gets rid of the opportunity for authenticity and selfhood. Jaspers' presentation of belief in an afterlife in order to avoid existential Angst reveals that he views the belief in an afterlife merely as a coping mechanism and an inauthentic one to boot. Indeed, Jaspers thinks there is no evidence for the existence of an afterlife. Instead, he states that there is evidence that we do not survive death: "mortality can be proven" (P2 197). Jaspers concludes that belief in an afterlife is a form of self-deception. Regardless of whether one agrees with him on this point, it raises a host of questions for Jaspers scholarship: Is death only existentially significant if there is no afterlife? If one believes in the afterlife for good reasons, then is it impossible to experience the boundary situation of death? If so, does this mean that religious people (or at least those who believe in an afterlife) have no opportunity to live authentically and to realize selfhood? Peach, for one, answers these questions on behalf of Jaspers in the affirmative:

Jaspers finds any belief in immortality, in the traditional sense, unfounded and false. Although for some it may be an effective way of combating the fear of death, Jaspers argues that this "unfounded false" belief will "transform the meaning of death as a boundary." That is, facing up to one's finitude will no longer be an existential boundary experience, and in his view, the boundary situation of death and one's opportunity to attain selfhood will thereby be diminished. [DDE 81]10

From the above follows that facing up to death with awareness is a necessary condition for realizing authenticity. Avoiding existential Angst in the just described ways are all forms of living inauthentically, that is, ways of living as though one were not mortal. The idea that avoiding existential Angst is an inauthentic way to live is reminiscent of Martin Heidegger's philosophy of death in Being and Time: "Our everyday falling evasion in the face of death is an inauthentic Being-towards-death."11

Critical Discussion

Jaspers' account of facing existential crises with courage and thereby achieving authenticity raises numerous questions. For example, Peach asks:

What exactly does it mean to face up to a boundary situation or live/experience it? Is it sufficient to reflect on it, or is the term "living" used in a more specific sense? Can anybody be said to be in a boundary situation without facing up to it? [DDE 64]

I will try to at least partly answer Peach's questions based on the above analysis of Jaspers' philosophy of death.

Living or experiencing a boundary situation amounts to having an existential crisis. Reflecting on existential crises in general or on someone else's existential crisis in particular is fundamentally different from having your own, and it has become clear from my reading of the second volume of his Philosophy that Jaspers thinks it is necessary to experience an existential crisis yourself in order to reap the potential benefits from it. Facing up to an existential crisis means facing up with courage to the existential Angst it raises rather than trying to avoid it. As Jaspers says, it seems possible for someone to have an existential crisis without facing up to it. An example of this, for Jaspers, would be resorting to belief in an afterlife when confronted with death.

Another question that presents itself is whether it suffices to achieve lasting authenticity by facing up to death once in a lifetime, or whether it happens to be an ongoing process. Jaspers has a clear answer to this question:

Courage cannot be a stable, permanent, stoical calm, for this would deplete Existenz. Our ambiguous existence, in which real truth does not endure, calls for composure to be constantly regained from pain. If I do not retain some sense of despair at the loss of those I loved most, I lose my Existenz as surely as one whom despair engulfs; if I forget my horror of nonbeing, I lose it as surely as one who dissolves in his fear. [P2 199]

For Jaspers, it is not enough to work through one existential crisis only; instead, it is necessary to continually face and accept one's mortality when striving to achieve authenticity: "Time and time again the pain of death must be felt, and each time the existential assurance can be newly acquired" (P2 199).

As to the question whether the achievement of authenticity requires one to experience this boundary situation, or whether other boundary situations (such as suffering or guilt) could bring about the same result, Jaspers' answer is not entirely clear. However, he does write that "the crucial boundary situation remains my death" (P2 195), and he seems to suggest that one cannot become an existential self without disappearance, that is, without the reality of death: "If there were no disappearance, my being would be endless duration rather than Existenz" (P2 193). In addition, Jaspers believes in the primacy of lived experience for authentic knowledge, so it would make sense that experiencing the boundary situation of death is necessary (or in any case extremely helpful) to gain the instrumental value associated with it. As the following passages show, Peach also seems to think that confronting one's own mortality with courage is a necessary condition for authenticity.

Existential Angst is the gateway to authentic existence. [DDE 80]

For Jaspers' existential philosophy boundary situations are prerequisites for the attainment of selfhood. As Jaspers often repeats, in order to achieve selfhood, the transformation of possible Existenz into actual Existenz has to occur in boundary situations. [DDE 82]

There would be no selfhood without the finitude of life and having to come to terms with it. [DDE 84]

Engagement with Analytic Existentialism

Jaspers' philosophy of death takes a different approach from most current work in analytic philosophy of death, which focuses on answering the following questions: Is death bad? Should we fear death? What happens when we die? Should we want to live forever? Although Jaspers does not explicitly address these questions, I will attempt to provide answers to them that are reflective of Jaspers' thought based on the previous analysis of his philosophy of death.

Like Epicurus, current analytic philosophy attempts to determine whether death is bad. More specifically, the issue is whether the state of being dead is bad for the one who dies. Some analytic philosophers hold the Epicurean view, mentioned above, according to which death is not bad for the one who dies. Other analytic philosophers argue that death does not have to be like anything in order for it to be bad. According to them, death is not bad because of any definite qualities that it has but because being dead deprives one of all the potentially good things in life. This is known as the deprivation theory.12 The deprivation theory is initially appealing, but it does face a problem: At which point in time, exactly, does death deprive one of the good things in life? Not while one is still alive, because then one is not deprived of good things; and not when one is dead, because then one will not exist. There is no other time at which death can deprive one of anything, so it seems that it cannot be a deprivation after all.

On the question of whether death is bad, it appears to me that Jaspers thinks that death is bad. Unlike proponents of the deprivation theory, however, Jaspers thinks that death is bad because it comes so often at the wrong time. It is a termination, for young and old alike, since a single human life becomes a narrative only for the bystander, never for the one who dies. Jaspers writes:

Real death, of course, is violent and cuts short; it is not a completion but a termination. [P2 200]

To complete life itself is to us an absurd notion. A life may have the character of completeness as a spectacle for others, but it never has that character in reality. [P2 200]

A similar idea can be found in the writings of Jean-Paul Sartre, and it is also one of Sartre's main reasons to think that death is bad. As Sartre argues, because death terminates life and the moment of death is not under one's control, the meaning of one's life can turn out very differently than intended.

Regarding the question of whether humans should fear death, such fear is natural but not rational according to the Epicurean view. This is because on this view death is not bad, and it is irrational to fear something that is not bad. Deprivationists, by contrast, often argue that fear of death is rational because, on their view, death is bad. However, Shelly Kagan has notably argued that even if death is a deprivation, fear is not an appropriate emotional response to it.13 This is because death is inevitable, and it only makes sense to fear something if the chance that it will occur is less than certain. Other emotions, such as sadness or gratitude, might be appropriate in that case, but fear is misplaced when there is no uncertainty. That being said, Kagan grants that it is rational to fear dying too soon. After all, this is a possibility but not a certainty, in which case it makes sense to fear its occurrence.

It seems to me that Jaspers would agree with the deprivationists, who hold that fear of death is rational, but for different reasons. For Jaspers, fear of death is rational, not because death is bad (although, according to him, it is), but because fear of death is necessary (and perhaps sufficient) for existential Angst, and existential Angst is necessary for authenticity. In other words, one should fear death because avoiding such fear leads to inauthentic ways of living.

In analytic metaphysics, much has been written about whether it is possible to survive death, and, if so, how this is possible. The result is different models based on different theories of human persons, what they are, and how they persist through time. For example, if humans are just their bodies, then the possible options for the afterlife are different than if they have immaterial souls.

To the question of whether humans can survive death, Jaspers provides a straightforward answer: "In fact, however, not only are all proofs of immortality faulty and hopeless, not only is probability in a matter of such absolute importance absurd, but mortality can be proven" (P2 197). One may disagree with Jaspers on this point, but the annihilation of the human person at death does seem to be his position.

The question of whether one should want to live forever is alive and well in contemporary analytic philosophy. Many papers have been written about the desirability of immortality in response to Bernard Williams' classic essay on the Makropulos case.14 Within this debate, the issue of whether immortality is required for life to be meaningful or, on the contrary, whether immortality deprives life of meaning takes center stage. Williams argues that an immortal life would become excruciatingly boring and lose all meaning. This is why he thinks that any rational person would eventually want to opt out, as Elina Makropulos does in Janacek's opera from which his paper takes its name. On the other hand, John Martin Fischer argues that there are repeatable pleasures that continue to be enjoyable no matter how often one experiences them. He holds that immortality is not so bad after all.15

Does Jaspers think that humans should want to live forever? As discussed above, Jaspers thinks that it is only because we die that we can achieve authenticity. If humans would be immortal, then one could not realize the full potential of one's existential self and would live forever as mere objective self. Jaspers regards this kind of "unexistential existence" as being a form of death, too. It is, in fact, worse than actual death. In Jaspers' words:

An existence coupled with the nonbeing of Existenz [that is, the existential self] raises the specter of an endless life without potential, without effect and communication. I have died, and it is thus that I must life forever; I do not live, and so my possible Existenz suffers the agony of being unable to die. The peace of radical nonbeing would be a deliverance from this horror of continual death. [P2 199]

Furthermore, Jaspers thinks that a balance between the objective self and the existential self ought to be maintained, and it is impossible to have merely an immortal existential self as the existential self depends on the objective self for its existence. In the end, Jaspers thinks that mortality is better than the alternative: although death is an untimely termination, immortality is a fate worse than death.16 Jaspers' view here is very similar to that of Beauvoir, who thinks that death is intrinsically bad but instrumentally good for, more or less, the same reasons as Jaspers.


In my attempt to open up Jaspers' philosophy to analytic philosophers, I have tried in this essay to provide an accessible account of his thoughts on death. Although this approach raises a number of questions about Jaspers' philosophy of death, nonetheless his philosophy of death weighs in on the main debates in analytic philosophy as outlined above. My hope is that this will make Jaspers relevant to contemporary discussions in the philosophy of death and that it will open up his work for further exploration. In my mind, the following two ideas have particularly great potential to enrich the analytic debate. First, lived experience plays a crucial role for Jaspers and this aspect is virtually missing from analytic philosophy. The concept of existential Angst and the idea that death is a test receive no attention in the analytic debate. In general, its focus is not on awareness of human mortality, on crises that death can induce, or on how to live given that each person is going to die. It is worth exploring whether something important is left out by a purely theoretical approach such as the analytical one. Second, a hotly contested question in the analytic debate is of whether death is necessary for a meaningful life: yet there is no discussion of the parallel question as to whether death is necessary for an authentic life. I think this is a question the analytic debate ought to consider. It does not seem unlikely that mortality is a necessary condition for many human values, and authenticity might be one of them.17

1 Karl Jaspers, Philosophy, Volume 2, transl. E. B. Ashton, Chicago, IL: University of Chicago Press, 1971. [Henceforth cited as P2]

2 Filiz Peach, Death, "Deathlessness" and Existenz in Karl Jaspers' Philosophy, Edinburgh, UK: Edinburgh University Press, 2008. [Henceforth cited as DDE]

3 Sigmund Freud, Reflections on War and Death, New York, NY: Moffat, Yard and Company 1918, p. 41. Hathi Trust online

4 Jean-Paul Sartre, Being and Nothingness: An Essay on Phenomenological Ontology, transl. Hazel E. Barnes, New York, NY: Philosophical Library 1958, p. 532. [Henceforth cited as BN].

5 Chris Thornhill and Ronny Miron, "Karl Jaspers," The Stanford Encyclopedia of Philosophy Archive (Spring 2020 edition), ed. Edward N. Zalta, (last accessed 6-28-2020).

6 Simone de Beauvoir, The Prime of Life, transl. Peter Green, London, UK: Penguin Books 1962, p. 602.

7 Usually, the distinction made between Angst and fear is that while fear has a concrete object, Angst does not have one. However, if one understands existential Angst in Jaspers' usage of the concept as being the fear of non-existence, as I think we should, then existential Angst does have a concrete object, namely non-existence. And yet, Jaspers speaks of existential Angst and not of existential fear. Arguably this is due to the word usage of Angst as having existential connotation whereas the word "fear" does not connote existentiality.

8 Thomas Nagel, "The Absurd," The Journal of Philosophy 68/20 (October 21, 1971), 716-727, here p. 719.

9 Epicurus, "Letter to Menoeceus," in The Stoic and Epicurean Philosophers: The Complete Extant Writings of Epicurus, Epictetus, Lucretius, Marcus Aurelius, ed. Whitney J. Oates, New York, NY: Random House 1940, p. 31. Archive online

10 Jaspers does believe in a form of deathlessness, but this is not a traditional afterlife or a genuine form of immortality. It is the idea that it is possible to experience eternity in a moment. In this way, Jaspers manages to safeguard a transcendental feature of human existence without adopting a belief in the immortality of the soul or an afterlife.

11 Martin Heidegger, Being and Time, transl. John Macquarrie and Edward Robinson, Oxford, UK: Blackwell 1962, p. 303.

12 A classic discussion of the Deprivation Theory can be found in Thomas Nagel, "Death," Nous 4/1 (February 1970), 73-80.

13 Shelly Kagan, Death, New Haven, CT: Yale University Press, 2012.

14 Bernard Williams "The Makropulos Case: Reflections on the Tedium of Immortality," in Problems of the Self, Cambridge, UK: Cambridge University Press 1973, pp. 82-100.

15 John Martin Fischer "Why Immortality Is Not So Bad," International Journal of Philosophical Studies 2/2 (1994), 257-270.

16 This assessment does not take into account possible alternatives to death and immortality.

17 I want to thank the audience of the first session of the KJSNA meeting at the 93rd Annual Meeting of the Pacific APA in Vancouver for helpful comments on an earlier draft of this paper. Special thanks to Tim Fitzjohn, Dane Sawyer, Joshua Tepley, and Helmut Wautischer.