Professor Cole is correct in his conclusion that the University of Pittsburgh Medical Center (UPMC) protocol does not violate requirements of "irreversibility" in criteria of death, but wrong about the reasons. "Irreversible" in this context is best understood not as an ontological or epistemic term, but as an ethical one. Understood that way, the patient declared dead under the protocol is "irreversibly" so, even though resuscitation by medical means is still possible. Nonetheless, the protocol revives difficult questions about our (...) concept of death. (shrink)

This paper studies the influence of agency conflicts on the irreversibility effect. Using a dynamic variant of the static Baron and Myerson :911–930, 1982) adverse selection model, we characterize under which circumstances the irreversibility effect arises in the presence and absence of an agency conflict. In particular, we find that in the presence of an agency conflict the irreversibility effect arises in more circumstances than in the standard first-best analysis that abstracts from agency problems.

There has been growing concern about whether individuals who satisfy neurological criteria for death or who become non-heart-beating organ donors are really dead. This concern has focused on the issue of the potential for recovery that these individuals may still have and whether their conditions are irreversible. In this article I examine the concepts of potentiality and irreversibility that have been invoked in the discussions of the definition of death and non-heart-beating organ donation. I initially focus on the recent (...) challenge by D. Alan Shewmon to accepting any neurological criterion of death. I argue that Shewmon relies on a problematic and unrealistic concept of potentiality, and that a better, more realistic concept of potentiality is consistent with accepting a neurological criterion for death. I then turn to an analysis of how the concept of irreversibility has been used in discussion of non-heart-beating organ donation. Similarly, I argue that some participants in this discussion have invoked a problematic and unrealistic concept of irreversibility. I then propose an alternative, more realistic account of irreversibility that explains how "irreversibility" should be understood in the definition and criteria of death. (shrink)

I discuss a broad critique of the classical approach to the foundations of statistical mechanics (SM) offered by N. S. Krylov. He claims that the classical approach is in principle incapable of providing the foundations for interpreting the "laws" of statistical physics. Most intriguing are his arguments against adopting a de facto attitude towards the problem of irreversibility. I argue that the best way to understand his critique is as setting the stage for a positive theory which treats SM (...) as a theory in its own right, involving a completely different conception of a system's state. As the orthodox approach treats SM as an extension of the classical or quantum theories (one which deals with large systems), Krylov is advocating a major break with the traditional view of statistical physics. (shrink)

This paper explores a distinction among causal relationships that has yet to receive attention in the philosophical literature, namely, whether causal relationships are reversible or irreversible. We provide an analysis of this distinction and show how it has important implications for causal inference and modeling. This work also clarifies how various familiar puzzles involving preemption and over-determination play out differently depending on whether the causation involved is reversible.

We discuss Boltzmann’s probabilistic explanation of the second law of thermodynamics providing a comprehensive presentation of what is called today the typicality account. Countering its misconception as an alternative explanation, we examine the relation between Boltzmann’s H-theorem and the general typicality argument demonstrating the conceptual continuity between the two. We then discuss the philosophical dimensions of the concept of typicality and its relevance for scientific reasoning in general, in particular for understanding the reduction of macroscopic laws to microscopic laws. Finally, (...) we reply to various common criticisms of the typicality account. (shrink)

Irreversibility, it is claimed, is a much broader concept than is entropy increase, as is shown by the occurrence of certain processes which are irreversible without seeming to involve any intrinsic entropy change. These processes include the spreading outwards into space of particles, or of radiation, and they also include certain biological and mental phenomena. For instance, the irreversible and treelike branching which is characteristic of natural evolution is not entropic when it is considered in itself—i.e. in abstraction from (...) accompanying biochemical and physiological activity. What appears to be the common feature of all forms of irreversibility is the fanning out of trajectories, new entities or new states, in the temporal direction towards the future. (shrink)

In this paper I examine Albert’s (2000) claim that the low entropy state of the early universe is sufficient to explain irreversible thermodynamic phenomena. In particular, I argue that conditionalising on the initial state of the universe does not have the explanatory power it is presumed to have. I present several arguments to the effect that Albert’s ‘past hypothesis’ alone cannot justify the belief in past non-equilibrium conditions or ground the veracity of records of the past.

Irreversible generalism, the view that reasons given for the evaluation of art are general and do not admit of exceptions, is defended from the criticisms levelled against it by George Dickie in ‘Reading Sibley’. The authors' view that Frank Sibley adhered to a form of reversible generalism, the view that reasons given for the evaluation of art are general but can sometimes become reasons to disvalue artworks, according to which there a criterion for distinguishing valenced from neutral aesthetic properties, is (...) also defended. (shrink)

Two distinct conceptions for the relation between reversible, time-reversal invariant laws of nature and the irreversible behavior of physical systems are outlined. The standard, extrinsic concept of irreversibility is based on the notion of an open system interacting with its environment. An alternative, intrinsic concept of irreversibility does not explicitly refer to any environment at all. Basic aspects of the two concepts are presented and compared with each other. The significance of the terms extrinsic and intrinsic is discussed.

The concept of irreversibility is central in several disciplines, from physics to biology and economics, as well as in many philosophical disputes. Yet, it is seldom clearly defined. In this article, it is argued that the thermodynamic framework with its concept of entropy – allegedly the hallmark of irreversibility – offers a formal framework for a thorough conceptualisation of irreversibility based on three (generic) parameters: (1) the openness of the systems and the possible interventions, (2) the (acceptable) (...) equivalence of the final state, and (3) the timeframe. Its usefulness for socio-ecological systems, and hence for sustainable development and sustainability science, will be shown by presenting how these generic parameters can be applied and interpreted in topics such as the precautionary principle, climate change mitigation and environmental aesthetics. (shrink)

Uffink and Valente claim that there is no time-asymmetric ingredient that, added to the Hamiltonian equations of motion, allows to obtain the Boltzmann equation within the Lanford’s derivation. This paper is a discussion and a reply to that analysis. More specifically, I focus on two mathematical tools used in this derivation, viz. the Boltzmann–Grad limit and the incoming configurations. Although none of them are time-asymmetric ingredients, by themselves, I claim that the use of incoming configurations, as taken within the B–G (...) limit, is such a time-asymmetric ingredient. Accordingly, this leads to reconsider a kind of Stoßzahlansatz within Lanford’s derivation. (shrink)

As soon as 'modernity' was defined as a particular way of con ceiving of time, the questions of tempo rality came to be situated at the heart of the ongoing debate regarding the legitimacy or illegitimacy of the 'modern age'. This has, in turn, readily led to a no less passionate search for the assessment of modernity's foundations which are thought to rest in its typical sense of experiencing temporality. This polemic instance, however, involves polarized perspectives and the consequent risk, (...) always present in dichotomous approaches, of oversimplifying the concepts at stake and smoothing over the intricacies of their history and meaning. Does there really exist something like a ' time of modernity'? This is the central question that the present article examines. 1 Key Words: evolution • modemity • philosophy of history • time irreversibility. (shrink)

The local aspect of the thermalization of thermal radiation due to the interaction of thermal radiation with matter is explored. It is shown that for absorption and emission interactions some well-known phenomenological statements of irreversible thermophysics are indeed relevant. For scattering interactions the entirely different picture that emerges is also briefly discussed. The local analysis is based on the concepts of temperature and entropy of nonequilibrium thermal radiation fields, as originally introduced by Planck, and shows that these concepts are susceptible (...) of a very natural thermodynamic interpretation. (shrink)

I. Prigogine has proposed, and the writings of N. S. Krylov to some extent suggest, a novel and unorthodox solution to foundational problems in statistical mechanics. In particular, the view claims to offer new insight into two interconnected problems: understanding the role of probability in physics, and that of reconciling the irreversibility of physical processes with the temporal symmetry of dynamical theories. The approach in question advocates a conception of the state of a system which incorporates features of the (...) quantum mechanical state concept in a context, classical statistical mechanics, where quantum considerations are generally considered to be irrelevant. I examine the plausibility of this new approach by offering an analysis of the various notions of state employed in modern physics. ;In the first chapter, I analyze the conceptual connections between dynamical laws and the nature of a system's state. I argue that laws and states are correlative. In constructing dynamical theories one does not start with a fixed or pre-determined state concept. Neither is one given the laws of the theory from which the conception of state is derived. Rather, we get the law/state structure as a "package." In light of this general analysis, I next examine the notion of state employed in the quantum theory. Here I consider a variety of conceptions of quantum states and assess their ability to answer the "paradoxes" of quantum theory. I pay particular attention to the role of probability and related restrictions on the realization of certain states. The new approach to statistical mechanics proposes to exploit similar restrictions on states in order to resolve the irreversibility problem. But is this unorthodox approach viable? In the final four chapters, I offer a detailed critique of this approach, examining the plausibility of the radical reworking of the state concept. I argue that while some important progress can be made, certain old puzzles remain, and new and difficult ones arise--ones which raise serious doubts about the ultimate success of this particular approach. I conclude, however, by arguing that such radical proposals are not unmotivated; and that novel and unorthodox proposals concerning the foundations of statistical mechanics must be taken seriously. (shrink)

«The chapter on «Times's Arrows» is a confusing blend of speculation and possibly wrong ideas.»From a review of M Gell‐Mann's «The Quark and the Jaguar» by P W Anderson in Physics World, August 1994.

The irreversibility effect implies that a decision maker who neglects the prospect of receiving more complete information at later stages of a sequential decision problem will in certain cases too easily take an irreversible decision, as he ignores the existence of a positive option value in favour of reversible decisions. This option value represents the decision maker's flexibility to adapt subsequent decisions to the obtained information. In this paper we show that the economic models dealing with irreversibility as (...) used in environmental and capital investment decision making can be extended to emergency response decisions that produce important irreversible effects. In particular, we concentrate on the decision whether or not to evacuate an industrial area threatened by a possible nuclear accident. We show in a simple two-period evacuation decision model that non-optimal conclusions may be drawn when evacuation is regarded as a `now or never decision'. The robustness of these results is verified by means of a sensitivity analysis of the various model parameters. The importance of `options thinking' in this decision context is illustrated in an example. (shrink)

Is the opposition to circumcision partly driven by cultural prejudices?In this issue of the Journal of Medical Ethics you can read a minisymposium on circumcision, mainly dealing with the circumcision of male children at an age where they cannot consent, but also touching upon issues of female genital mutilation.When reading the papers I found it strange, but of course not really surprising given its symbolic importance, that we are so worried about interventions on the male penis. Why are we not (...) equally worried about other irreversible bodily and mental interventions to which parents subject their children? I will not dwell on the irreversible mental imprinting, apart from mentioning that upon becoming a father I was amused to find that certain Danish lullabies and children’s rhymes had apparently been stored in my mind for the last 40 …. (shrink)

QED is a fundamental microscopic theory satisfying all the conservation laws and discrete symmetries C, P, T. Yet, dissipative phenomena, organization, and self-organization occur even at this basic microscopic two-body level. How these processes come about and how they are described in QED is discussed. A possible new phase of QED due to self-energy effects leading to self-organization is predicted.

The popularization of the term “clinical death” for the absence of vital signs suggests the possibility of a radical change in our understanding of death. While death used to be considered something that we do not have the power to reverse, contemporary optimism suggests that we may be able to restore life to a dead organism. In this article, I examine how the term “death” is used today to clarify what kind of irreversibility we ought to assign to it. (...) I conclude that the kind of irreversibility closest to our concept of death is one that depends on implicit metaphysical commitments: we generally treat death as though it were metaphysically irreversible, and therefore not reversible by us. (shrink)

The author proposes to show that the actual crisis in microphysics is principally due to the fact that, as quantum mechanics is a theory of stationary states and reversible movements, it fundamentally ignores the notion of a transitory process. The essential characteristic of quantum theories is the result of an evolution of more than two centuries; a period of development essentially devoted to the description of stationary and reversible phenomena. The author's point of view, which reflects that of the school (...) of Louis de Broglie, is that microphysics must now cross a new threshold in giving up the description of stationary states and the calculation of their transition probabilities in favor of attempting to describe the transitions themselves and explain the origin and stability of stationary states. The future seems to him to be one of a microphysics based on irreversibility. (shrink)

The aim of this paper is to analyze time-asymmetric quantum mechanics with respect of its validity as a non time-reversal invariant, time-asymmetric theory as well as of its ability to determine an arrow of time.

Brownian computers are supposed to illustrate how logically reversible mathematical operations can be computed by physical processes that are thermodynamically reversible or nearly so. In fact, they are thermodynamically irreversible processes that are the analog of an uncontrolled expansion of a gas into a vacuum.

We present a new formalism for the microscopic classical electrodynamics of point charges in which the dynamic absence of self-interactions is enforced by the action principle, without eliminating the field degrees of freedom. In this context, free local radiation fields are dynamically prohibited. Instead radiation is carried by charge-field functionals of the current which have a negative parity under mathematical time reversal. This leads to the dynamic requirement of a physical time arrow in the equations of motion in order to (...) preserve the overall mathphysical time-reversal symmetry of the formalism. Since this physical time arrow emerges electrodynamically without the need of external thermodynamic or cosmological criteria, it offers a dynamical explanation for the origin of irreversibility in classical electrodynamic measurement processes. “Science, like the arts, admits aesthetic criteria; it seeks theories that display ‘a proper conformity of the parts to one another and to the whole’ while still showing some strangeness in their proportion”—S. Chandrasekar. (shrink)

The distinction between the "permanent" (will not reverse) and "irreversible" (cannot reverse) cessation of functions is critical to understand the meaning of a determination of death using circulatory–respiratory tests. Physicians determining death test only for the permanent cessation of circulation and respiration because they know that irreversible cessation follows rapidly and inevitably once circulation no longer will restore itself spontaneously and will not be restored medically. Although most statutes of death stipulate irreversible cessation of circulatory and respiratory functions, the accepted (...) medical standard is their permanent cessation because permanence is a perfect surrogate indicator for irreversibility, and using it permits a more timely declaration. Therefore, patients properly declared dead in donation after circulatory death (DCD) protocols satisfy the requirements of death statutes and do not violate the dead donor rule. The acronym DCD should represent organ "donation after circulatory death" to clarify that the death standard is the permanent cessation of circulation, not heartbeat. Heart donation in DCD does not retroactively negate the donor's death determination because circulation has ceased permanently. (shrink)

Should the process of ecological restoration be considered a type of moral reparation? In a recent issue of this journal, Ben Almassi (2017) has argued that ecological restoration should be understood as a moral repair, i.e., as "a model for rebuilding the moral conditions of relationships" (20). Ideas of restorative justice and moral repair are appropriate to address human injustice and wrongdoing. But these concepts are vacuous and lose their meaning when addressing the ethics of human activities regarding the natural (...) world because of the essential character of the restoration process: the replacement or substitution of new entities for pre-existing entities in an attempt to reverse the irreversible. At best, the idea of moral reparations to nature is a weak metaphor with no practical efficacy; at worst, it totally misconceives the relationship between human activity and the natural environment in the process of ecological restoration and provides yet another dangerous and disingenuous justification of human arrogance and domination of the natural world. In the guise of the act of moral reparations, humans are instead attempting to assume the powers of God, to control the natural and human world. My previous criticisms of the ethics and meaning of ecological restorations—especially regarding the substitution of new individuals and the artifactual nature of restorations—can be used to undermine Almassi's thesis of moral repair as a goal of ecological restoration practice. In addition an analysis of the Book of Job in the Old Testament demonstrates that not even God—much less humans—can restore and replace what has been destroyed. (shrink)

This book concentrates on the properties of the stationary states in chaotic systems of particles or fluids, leaving aside the theory of the way they can be reached. The stationary states of particles or of fluids (understood as probability distributions on microscopic configurations or on the fields describing continua) have received important new ideas and data from numerical simulations and reviews are needed. The starting point is to find out which time invariant distributions come into play in physics. A special (...) feature of this book is the historical approach. To identify the problems the author analyzes the papers of the founding fathers Boltzmann, Clausius and Maxwell including translations of the relevant (parts of ) historical documents. He also establishes a close link between treatment of irreversible phenomena in statistical mechanics and the theory of chaotic systems at and beyond the onset of turbulence as developed by Sinai, Ruelle, Bowen (SRB) and others: the author gives arguments intending to support strongly the viewpoint that stationary states in or out of equilibrium can be described in a unified way. In this book it is the "chaotic hypothesis", which can be seen as an extension of the classical ergodic hypothesis to non equilibrium phenomena, that plays the central role. It is shown that SRB - often considered as a kind of mathematical playground with no impact on physical reality - has indeed a sound physical interpretation; an observation which to many might be new and a very welcome insight. Following this, many consequences of the chaotic hypothesis are analyzed in chapter 3 - 4, and in chapter 5 a few applications are proposed. Chapter 6 is historical: carefully analyzing the old literature on the subject, especially ergodic theory and its relevance for statistical mechanics; an approach which gives the book a very personal touch. The book contains an extensive coverage of current research (partly from the authors and his coauthors publications) presented in enough detail so that advanced students may get the flavor of a direction of research in a field which is still very much alive and progressing. Proofs of theorems are usually limited to heuristic sketches privileging the presentation of the ideas and providing references that the reader can follow, so that in this way an overload of this text with technical details could be avoided. (shrink)

It is a remarkable fact that all processes occurring in the observable universe are irre- versible, whereas the equations through which the fundamental laws of physics are formu- lated are invariant under time reversal. The emergence of irreversibility from the funda- mental laws has been a topic of consideration by physicists, astronomers and philosophers since Boltzmann's formulation of his famous \H" theorem. In this paper we shall discuss some aspects of this problem and its connection with the dynamics of (...) space-time, within the framework of modern cosmology. We conclude that the existence of cosmological horizons allows a coupling of the global state of the universe with the local events deter- mined through electromagnetic processes. (shrink)

In the case of the irreversibly comatose patient, though no personal consciousness remains, some moral duty is owed the remaining biological life. Such an ending to human life, if pathetic, is also both intelligible and meaningful in a biological and evolutionary perspective. By distinguishing between the human subjective life and the spontaneous objective life, we can recognize a naturalistic principle in medical ethics, contrary to a current tendency to defend purely humanistic norms. This principle has applications in clinical care in (...) the definition of death, in the use of life support therapy, in distinguishing ordinary from extraordinary therapy, in evaluating euthanasia, and in the extent of appropriate medical intervention in terminal cases. CiteULike Connotea Del.icio.us What's this? (shrink)

This paper considers the issue of cryopreservation and the definition of death from an Aristotelian-Thomistic perspective. A central conceptual focus throughout this discussion is the purportedly irreversible nature of death and the criteria by which a human body is considered to be informed by a rational soul. It concludes that a cryopreserved corpse fails to have “life potentially in it” sufficient to satisfy Aristotle’s definition of ensoulment. Therefore, if the possibility that such a corpse may be successfully preserved and resuscitated (...) comes to fruition, one would have to conclude that the person’s rational soul, which had separated from its body at death, has literally reanimated its resuscitated body. Obviously, this conclusion has theological implications that go beyond the scope of this discussion if we regard bodily resuscitation in this manner as a form of technologically induced resurrection. Another apparent implication of the paper’s argument is that, in a limited sense, death loses its irreversible nature. (shrink)

There are currently two legally established criteria for death: the irreversible cessation of circulation and respiration and the irreversible cessation of neurologic function. Recently, there have been technological developments that could undermine the irreversibility requirement. In this paper, I focus both on whether death should be identified as an irreversible state and on the proper scope of irreversibility in the biological definition of death. In this paper, I tackle the distinction between the commonsense definition of death and the (...) biological definition of death to show that even the commonsense concept of death is specified by biological facts. Resting on this argument, I argue that any definition of death is a posteriori. Thus, irreversibility is part of any definition of death because the actual phenomenon of death is irreversible. In addition, I show that the proper domain of irreversibility in a definition of death is circumscribed by physical possibilities and that irreversibility in the definition of death refers to current possibilities for the reversal of relevant biological processes. I conclude that, despite recent technological advancements, death is still irreversible. (shrink)

It has been a longstanding problem to show how the irreversible behaviour of macroscopic systems can be reconciled with the time-reversal invariance of these same systems when considered from a microscopic point of view. A result by Lanford shows that, under certain conditions, the famous Boltzmann equation, describing the irreversible behaviour of a dilute gas, can be obtained from the time-reversal invariant Hamiltonian equations of motion for the hard spheres model. Here, we examine how and in what sense Lanford’s theorem (...) succeeds in deriving this remarkable result. Many authors have expressed different views on the question which of the ingredients in Lanford’s theorem is responsible for the emergence of irreversibility. We claim that these interpretations miss the target. In fact, we argue that there is no time-asymmetric ingredient at all. (shrink)

Most definitions of death – whether cardiopulmonary, whole brain and brain stem, or just upper brain – include an irreversibility condition. Cessation of function is not enough to declare death. Irreversibility should be limited to an organism's ability to ‘restart’ itself after vital organs have ceased to function. However, this would mean that every hour people who cannot be revived without the intervention of medical personnel and their technology are coming back from the dead. However, the alternative of (...) irreversibility being dependent upon technology will lead to even more counterintuitive results such as: some people are dead at a particular time and place, but others in more technologically advanced eras and locations are alive despite their being in identical physical states; in the future, millions of cryogenically frozen human beings could spend centuries in a non–dead state because of the future technological breakthroughs; or large numbers of ‘frozen’ people are dead for aeons but coroners are not able to declare them so because they are unaware of what biological conditions science will never be able to reverse. So death should be defined only in non–relational biological terms with a self–starting condition similar to that once advocated by Lawrence Becker. (shrink)

Various arguments have been given against positive euthanasia, but little attention has been given to the question of whether these arguments are uniformly effective in all contexts. There appears to be a range of cases, involving non-voluntary killing of irreversibly unconscious patients, in which these arguments do not succeed. Various reasons have been given in support of positive killing in such cases. It can be argued that there is a range of cases for which a policy of allowing positive killing (...) is morally required. However, currently there are legal obstacles to implementing such a policy. (shrink)

From both physical and epistemological viewpoints, the following theses, which nowadays are often discussed in the literature, are examined: Nonlinear thermodynamics renders it possible to grasp evolutionary physical processes; for thermodynamics it introduces, instead of idealized reversible time, a directed time into physics; thus a science is established that is nearer to reality than classical physics. To analyze these theses, the relation of thermodynamics to dynamical physics is considered. In particular, it is demonstrated that, in classical as well as in (...) modern thermodynamics, irreversibility is introduced via conditions which must be formulated in addition to the dynamical laws. To show the reason for this, the epistemological status of the physical time conception is analyzed, and its character as a physical measurement quantity is established. (shrink)

Singer claims that there are two ways of challenging the fact that brain-dead patients, from whom organs are usually retrieved, are in fact biologically alive. By means of the first, the so called dead donor rule may be abandoned, opening the way to lethal organ donation. In the second, it might be posited that terms such as “life” and “death” do not have any primary biological meaning and are applicable to persons instead of organisms. This second possibility permits one to (...) acknowledge that brain-dead patients are deceased because they are irreversibly unconscious. In the commentary which follows, I will argue that Singer’s second option is preferable since it provides a higher amount of organs available for transplant, and is better suited to the meaning of “death” which occurs in ordinary language. I will also defend such a concept of death against the objections raised by Michael Nair-Collins in the article Can the brain-dead be harmed or wronged? On the moral status of brain death and its implications for organ transplantation. (shrink)

The concept underlying Prigogine's ideas is the asymmetric "lifetime" he introduces into thermodynamics in addition to the symmetric time parameter. By identifying processes by means of causal chains of genidentical events, we examine the intrinsic order of lifetime adopting Grunbaum's symmetric time order. Further, we define the physical meaning and the actuality of the processes under consideration. We conclude that Prigogine's microscopic temporal irreversibility is tacitly assumed at macroscopic level. Moreover, his "new" complementarity lacks any scientific foundation. Finally, we (...) put forward the fact-like origin of temporal irreversibility referring to classical thermodynamics. (shrink)

The reversibility problem (better known as the reversibility objection) is usually taken to be an internal problem in the kinetic theory of gases, namely the problem of how to account for the second law of thermodynamics within this theory. Historically, it is seen as an objection that was raised against Boltzmann's kinetic theory of gases, which led Boltzmann to a statistical approach to the kinetic theory, culminating in the development of statistical mechanics. In this paper, I show that in the (...) late nineteenth century, the reversibility problem had a much broader significance - it was widely discussed and certainly not only as an objection to Boltzmann's kinetic theory of gases. In this period, there was a conflict between mechanism and irreversibility in physics which was tied up with central issues in philosophy of science such as materialism, empiricism and the need for mechanistic foundations of physical theories, as well as with concerns about the heat death of the universe. I discuss how this conflict was handled by the major physicists of the period, such as Maxwell, Kelvin, Duhem, Poincaré, Mach and Planck, as well as by a number of lesser-known authors. (shrink)

This essay examines the claim “path dependence entails irreversibility” from the point of view of evolutionary biology. I argue that evolutionary irreversibility possesses many faces, sometimes conflicting with path dependence. I propose an account of path dependence that does not rely on irreversibility and explains why it more naturally coexists with the notion of (contingent) irreversibility developed by the Belgian paleontologist Louis Dollo. However, I argue that we should not conceive of this relationship as necessary.