Anti-Realism

Scientific realism is the view that science aims to provide us, in its theories, with a literally true account of the nature of the objective world. Anti-realism rejects this, and claims that science provides, at most, a convenient model that accounts for the phenomena in the observable world. One anti-realist position, namely the constructive empiricism of Bas van Fraassen (1980), states that theories aim to be empirically adequate, and the acceptance of a theory involves no more than the belief that it is empirically adequate. The following are the arguments against scientific realism.

Underdetermination

The formation of scientific theories involves two main steps. First is the gathering of empirical data acquired through observation, and second is the construction of the theory that accounts for this data via an inferential process. The second step is non-deductive. Hence, the theory is not entailed by the data. Rather, it goes beyond the data to account for and unify it.

As noted by van Fraassen in The Scientific Image (1980), this allows the underdetermination of theory by data. Since the empirical data does not entail the theory, there can be several different competing theories that each accounts for it. Furthermore, since each of these theories are based on and account for the same data, the scientist cannot select one theory from a set of theories from the data alone. The theories are empirically equivalent, and so extra premises are required to select a theory in favour of its rivals. These are known as superempirical virtues.

In The Scientific Image, van Fraassen argues that these superempirical virtues that are used to select a theory from its empirically equivalent rivals do not reflect the truth of the theory, but rather its pragmatic usefulness and æsthetic appeal. Simplicity is a good example of such a superempirical virtue. The principle of Ockham's razor states that a theory should not multiply properties unnecessarily, and so simple theories are favoured over their empircally equivalent but complex rivals. However, this is for pragmatic and æsthetic reasons, rather than a reflection of the theory's truth-conduciveness. Simplicity makes the theory more comprehensible, convenient, and satisfying to the human mind. In fact, the claim that simplicity is an indicator of the truth of a theory has no justification unless one already knows that the world is simple.

The Pessimistic Meta-Induction

This argument is championed by Larry Laudan in his paper "A Confutation of Convergent Realism" (1981). He states that for a theory to be true, it must be empirically successful, and its terms must refer to actual phenomena in the objective world. If the theory is not empirically successful, it cannot be true, since it contradicts our experience of the world. Similarly, if a theory's terms do not refer to actual phenomena, it cannot be true, since it directly contradicts the nature of the world.

Laudan presents an extensive list of past theories which were once empirically successful. Furthermore, the terms of these theories, in their time, were considered to refer to actual phenomena, but are now considered not to refer. In other words, these theories were once considered to be true, but are now considered false. Among these theories are the celestial sphere theory, the phlogiston theory, and the luminiferous æther theory.

Using induction, Laudan argues that since these previously accepted and once empirically successful theories were subsequently considered false, current and future accepted and empirically successful theories will also subsequently be considered false. In other words, modern theories may at present have empirical and predictive success, but so did previous theories in their day. These previous theories have since been rejected, and so by induction it is likely that modern theories will too be rejected. This principle extends not only to current theories, but also to all future theories. Therefore, since all current and future theories will subsequently be rejected, realism is false.

Verisimilitude

The pessimistic meta-induction suggests that the empirical success of a theory does not guarantee that its central terms refer to actual phenomena, and so does not guarantee its truth. One of the realist objections to this argument refers to the notion of approximate truth, or verisimilitude. Although the empirical success of a theory does not guarantee its absolute truth, it does indicate that the theory is at least approximately true. Furthermore, although past empirically successful and hence approximately true theories have been rejected, they have been rejected in favour of new theories which are even closer to the truth. Thus, scientific knowledge is cumulative in the sense that newer theories are more approximately true than their predecessors.

The anti-realist argument against this claim is that the concept of verisimilitude is arbitrary and meaningless. As Laudan points out, there has been no successful definition of what it means for a statement to be approximately true. For example, consider a glass of water. One person states that it is a bottle of water, while another states that it is a glass of whiskey. Which statement is closer to the truth? The first is closer with respect to the type of liquid, whereas the second is closer with respect to the type of container. Nevertheless, both statements are strictly false. This suggests that the notion of verisimilitude is arbitrary, and so it is meaningless to claim that one theory is closer to the truth than another.

This argument holds even for numbers. For example, is 8 closer to 7, 4, or 3? One may argue that it is closest to 7 because of the smallest numerical difference. However, one may also argue that it is closer to 4 because 8 is a multiple of 4, or that it is closer to 3 because both the figures 8 and 3 contain curved lines. Nevertheless, none of these numbers equals 8.

What this critique of verisimilitude illustrates is that statements which are considered to be approximately true are actually strictly false, and to claim that one false theory is closer to the truth than another is arbitrary and meaningless. Therefore, scientific knowledge is not cumulative, and realism is false.

The Incommensurability Thesis

In The Structure of Scientific Revolutions (1962), Thomas Kuhn argues that the evolution of scientific theory does not follow a linear process of the accumulation of knowledge, but involves non-linear paradigm shifts as a result of changing intellectual circumstances. Kuhn distinguishes two types of scientific activity. Firstly, normal science involves routine problem-solving within an accepted framework of meanings, concepts, and interpretations, known as a paradigm. Secondly, revolutionary science occurs when the accumulation of anomalous data casts doubt on the success of the current paradigm, and involves a shift to a new paradigm when a sufficient number of the scientific community are persuaded that the new paradigm is preferable to the old. Examples of paradigm shifts include the shift from Newtonian mechanics to Einsteinian relativity, the shift from Ptolemaic cosmology to Copernican cosmology, the shift from the phlogiston theory of combustion to Lavoiser's theory of chemical reactions, and the shift from classical physics to quantum mechanics.

Kuhn argues that because any two paradigms are so radically different from each other, there is no meaningful way to compare them objectively. In other words, different paradigms have different meanings of terms and concepts, different interpretations of data, and different values. Therefore, there are no common measures by which they can be objectively compared. This is the principle of incommensurability.

For example, although the concept of mass features in both Newtonian mechanics and Einsteinian relativity, the term has a different meaning in each paradigm. Therefore, the two paradigms cannot be compared in a meaningful way with respect to the term mass. Furthermore, consider the fact that all observation is influenced by the background framework under which it is observed. Because of the theory-ladenness of observation, empirical data is interpreted differently in each paradigm. Therefore, empirical data cannot be used to favour one paradigm over another. Finally, different paradigms have different criteria and values for what constitutes a good theory. Therefore, any two paradigms cannot be compared with each other objectively, because they possess different values for comparison.

Because one paradigm cannot objectively be considered better or worse than another paradigm, it follows that scientific knowledge is not cumulative. Different paradigms have different criteria for the validity of theories, and so there is no objectively meaningful and independent means by which one theory can be considered more or less valid than another. Therefore, realism is false.

Conclusions

The anti-realist arguments considered here claim that scientific theories are not representative of objective truth, but provide a means of accounting for phenomena that we observe in a convenient and comprehensible way. The virtues that influence our decisions in a choice between competing theories are not truth-conducive, but pragmatic, æsthetic, and social. Nevertheless, this does not make them any less valid reasons for choosing a theory, for the theory’s reception, understanding, and application are greatly aided by these virtues. Theories, after all, despite their incapability to provide us with a literal account of objective truth, serve to facilitate our judgements about the world, and so, it is a given requirement that they be pragmatic.

References

• Kuhn TS (1962). The Structure of Scientific Revolutions. Chicago: University of Chicago Press.
• Laudan L (1981). "A Confutation of Convergent Realism". Philosophy of Science, 48:1, 19-49.
• van Fraassen BC (1980). The Scientific Image. Oxford: Clarendon Press.
  

Dualism

"The lifeless landscape that is the scientific domain, that location of transactions of energy moving between constituent bits and pieces, seems to afford no obvious home for the mental."

Thus wrote the particle physicist John Polkinghorne in his book Beyond Science: The Wider Human Context (1996). Many a hard-headed scientist would claim that Polkinghorne’s comment does not necessarily hold to be the case. Indeed, advances in the medical sciences have undeniably facilitated our understanding of the workings of our bodies, and this understanding has enhanced our capacity to relieve suffering and prolong life. But in addition to this, remarkable progress has also been made in the science of the mind: recent work in cognitive psychology has provided much insight into the processes involved in the generation of our thought and behaviour, while the neurosciences have located many of the brain structures and neural mechanisms that are correlated with various aspects of our mental activity.

However, despite this progress, Polkinghorne’s comment may, to an extent, be justified. If we take a look at what kind of knowledge is provided to us by the cognitive sciences, we can classify it as being structural and dynamical knowledge about the functional aspects of the mind. Cognitive science tells us how the mind works: neurophysiology informs us of the brain structures and neural mechanisms that underlie our perception and behaviour; explorations into the brain’s biochemistry reveal the molecular basis of these neural mechanisms; the various schools of psychology are interested in the causal dynamics involved in the generation of thought and behaviour. In essence, the facts used to explain these functional aspects of the mind are facts about the structure and dynamics of the brain: they relate to physical mechanisms that occur inside our heads. For the purpose of accounting for the functional aspects of the mind, these facts appear to be adequate. After all, these aspects, such as information processing and the generation of behaviour, are themselves structural and dynamical phenomena. Thus, it makes sense that structural and dynamical facts yield further structural and dynamical facts.

However, while physical facts appear to be sufficient in the explanation of these functional aspects of the mind, there remains the niggling impression that something has fundamentally been left out of the picture. That something, I argue, is consciousness. As well as the functional aspects of the mind involved in the generation of thought and behaviour, there is also a subjective aspect, relating to how a mental state feels qualitatively. For example, when I look at a bright orange sunset, there takes place, in my brain, an intricate bustle of neural activity and information processing, perhaps even resulting in a behavioural response such as smiling and sighing at this beautiful view. However, in addition to this neural processing, I also have a subjective experience of the orange sunset. The 'orangeness' has a particular qualitative feel, or as put by contemporary philosopher Thomas Nagel (1986), there is "something it is like" to have a conscious experience. The following arguments illustrate the irreducibility of such a phenomenon to physical explanation.

The Knowledge Argument

The basic underlying assumption of the knowledge argument is that full knowledge about the subjective quality of experience can be acquired only by having the experience oneself. No amount of physical knowledge of the structure and dynamics of the stimulus that causes the experience, or of what happens in the brain when one has such an experience, entails what the experience is like qualitatively. It follows from this that the physical facts do not exhaust the phenomenal facts, and so, physicalism is false.

This argument is perhaps most vividly presented by Frank Jackson (1982) in the hypothetical case of Mary, the colour scientist who has spent her entire life in a monochrome environment, exclusively coloured in black, white, and shades of grey. Consequently, Mary has never subjectively experienced the colour red before. Nevertheless, perhaps via black and white television, she has become the world’s leading expert on colour perception, and knows everything physical that occurs inside a perceiver’s brain when he or she perceives red. Furthermore, Mary lives in a time in which we have a completed physics, and so, also has learned everything physical about the structure and dynamics of red light. Mary, therefore, can be said to have the complete knowledge of the physical facts about the colour red and its perception.

However, as Jackson argues, she does not have the complete facts about red experience, since she cannot infer, from the physical facts, the subjective quality of a red experience. She knows all about the structure and dynamics of red light and red perception, but having never experienced red herself, she does not know what red is like qualitatively. Thus, Jackson proposes that if Mary is released from her monochrome compound into the great wide world of colour, in which she sees the colour red for the first time, she gains knowledge that she did not possess before. This knowledge is of the subjective quality of red experience, and since Mary already possessed the complete physical knowledge of the colour red and its perception, this new knowledge she gains must be non-physical. The conclusion from this is that there exist phenomenal facts over and above the complete physical facts, and that these phenomenal facts cannot be explained by, or identified, with the physical facts. Thus, physicalism is false.

The Zombie Argument

This argument once again defends the idea that consciousness is not logically supervenient on the physical. As has been shown by the knowledge argument, even when the complete physical facts are established, the question of whether consciousness is present is left entirely open. The physical facts do not entail the presence of consciousness, and so it follows that consciousness is an extra fact over and above the physical. From this, the ‘zombie argument’ proposes that given any physical system, such as the brain, it is always logically conceivable that such a system entirely lacks consciousness. The reasoning behind this is that when considering the physical facts of a system, the presence of conscious experience is a superfluous detail. One can explain the structure and dynamics of a physical system in full without having to refer to subjective experience at all. Therefore, there is no contradiction in conceiving of such a system as having or lacking conscious experience. Subjective qualities make no difference to the structure and dynamics of a system.

This argument is championed by David Chalmers in his 1996 book The Conscious Mind, in which he argues for the logical conceivability of zombies, organisms physically identical to human beings, but completely lacking in consciousness. He considers the idea of a zombie twin, which is physically identical to him, but with the major difference that he himself is conscious, whereas his zombie twin is not. Since his zombie twin is physically identical to Chalmers, they both function in identical ways. The same stimuli bring about the same neural mechanisms in both their brains, and consequently they both have the same reactions and display the same behaviour. The only difference is that Chalmers’ functioning is accompanied by consciousness, whereas his zombie twin’s is not. The neural mechanisms in Chalmers’ brain are accompanied by subjective experiences, whereas there is no experience at all in the case of his zombie twin.

Chalmers argues that there is no logical contradiction in this seemingly peculiar situation. The functioning of an organism depends on its physical properties of structure and dynamics, and nothing in these structural and dynamical properties entails the presence of subjective experience. It is perfectly conceivable to realise a functional system purely in structure and dynamics, without having to bring up consciousness at all. Therefore, given the complete physical facts about a functional system, the existence of consciousness is an extra fact over and above the physical facts. From this, it also follows that the physical facts cannot help us to distinguish Chalmers from his zombie twin, since they are physically identical. In fact, since Chalmers’ consciousness is only accessible to him in first-person, we have no access to it, and so it follows that we cannot distinguish him from his zombie twin at all.

The Explanatory Gap Argument

Whereas the zombie argument focuses on the actual existence of consciousness, the explanatory gap argument focuses on the subjective quality of particular conscious experiences. From this reflection on the qualitative nature of experiences, conclusions are drawn about their relation to physical events in the brain. Since it is plain reflection on subjective experience, rather than the postulation of logical thought experiments, which provides the substance for this argument, its strength appears to come from its intuitive appeal, rather than from its path of reasoning.

So, let us consider the qualitative nature of a subjective experience, such as that of seeing the colour red. I am not talking about any physical properties of the colour red, such as its wavelength or the neural processes that occur upon its perception. I am concerned here about the actual subjective quality of the experience of red. Upon reflection, it is clear that such an experience is arbitrary. It has no structure, for it is itself a basic simple. It is itself a unique phenomenon of its own kind, and so any connection between it and anything else cannot be anything but arbitrary. It follows that there is no explanatory connection between physical events in the brain and the qualitative nature of subjective experience. Physical information cannot explain subjective experience, and so physicalism is false.

Although championed by Joseph Levine (1983), the idea of qualia as arbitrary was first emphasised by the seventeenth century British empiricist John Locke. Locke, in An Essay Concerning Human Understanding (1690), states that the ideas which are evoked by secondary qualities, such as the experiences of colour, smell, and taste, bear no relation to the events in the objective world that evoke in our minds such qualities. Rather, these ideas and their corresponding physical events are merely correlated in an arbitrary manner. To further expose this explanatory gap between the physical and the phenomenal, Levine suggests the logical possibility of the spectral inversion of visual qualia, while one’s physical functioning remains the same.

Perhaps the most vivid way to illustrate this is to consider a thought experiment described by Chalmers, in which we are presented with a hypothetical conscious being, who is physically and functionally identical to you or me, but whose visual qualia are inverted. In other words, in situations in which you or I would have a red experience, this being will have a blue experience. Nevertheless, its functioning remains indistinguishable to ours. It possesses the same neural mechanisms of colour processing as you and me, and consequently displays the same behaviour in response to seeing a red object. The only difference is that the phenomenal qualities that accompany this functioning are different.

Levine and Chalmers argue that there is no logical contradiction here. Nothing in the physical functioning of the brain dictates that one type of processing should be accompanied by one particular type of experience over another. Red processing with blue phenomenology is just as coherent as red processing with red phenomenology. The accompanying qualia make no difference to the structure and dynamics of neural function, and so are extra facts over and above any physical information.

Kripke's Argument

In his 2000 book Thinking about Consciousness, Papineau presents the so-called ‘identity thesis’, as put forward by Place (1957) and Smart (1959). This states that there is an identity between qualitative experiences, such as pain, and certain neural states, such as the firing of C-fibres, much like how there is an identity between water and H₂O. Furthermore, according to the identity thesis, both of these identities are contingent, for neither of the statements ‘pain is the firing of C-fibres’ and ‘water is H₂O’ are known a priori, but are only made known through scientific discovery. The fact that water is H₂O is not an analytic statement, but something that had to be discovered by scientists. Likewise, it was also a discovery that the firing of C-fibres results in pain, as was Papineau’s example that the names ‘Mark Twain’ and ‘Samuel Clemens’ refer to the same person.

An argument against the identity thesis is put forward by Saul Kripke (1980), who asserts that all identities are necessary, provided that the terms being used to pick out the objects designate rigidly. Water is necessarily H₂O, for the identity holds in every possible world. According to Kripke, any appearance of contingency is just an illusion. Indeed, the fact that water is H₂O was something that needed to be discovered, and so it seems natural to suggest that water might not have turned out to be H₂O. In other words, although water turned out to be H₂O in this world, one may speculate that there may be a possible world in which water did not turn out to be H₂O, but instead turned out to be XYZ. However, Kripke argues that this is contradictory, for water is H₂O in every possible world. In fact, the substance imagined in this other world is in water at all, but is a substance that behaves like water, made out of XYZ. One may call this substance ‘watery stuff’. However, for something to be water, it must be made out of H₂O, and since this ‘watery-stuff’ is not made out of H₂O, it cannot be water. Therefore, Kripke’s proposal suggests that water is necessarily H₂O, but this does not mean that every possible world contains water.

However, in the case of the experience of pain and the firing of C-fibres, Kripke argues, there is no necessary identity, for whereas water is H₂O in every possible world, we can conceive of possible worlds in which the experience of pain is not accompanied by the firing of C-fibres, and conversely, worlds in which the firing of C-fibres is not accompanied by the experience of pain. Furthermore, since all identities which involve rigid designators must be necessary, it follows that there is no identity between the experience of pain and the firing of C-fibres. This, I argue, is because the experience of pain and the firing of C-fibres essentially refer to different phenomena. Whereas the firing of C-fibres refers to the neural mechanisms that occur when one is stimulated with noxious stimuli, the experience of pain refers to the subjective quality of pain itself. Therefore, it appears logically conceivable to dissociate the two.

As we saw earlier in my discussion of the zombie argument, we can conceive of the firing of C-fibres without any reference to the subjective quality of a painful experience. This cannot be done in the case of water and H₂O, for water’s molecular structure of H₂O is essential to it. It follows that whereas a substance which behaves like water, but is not made from H₂O, is not water, but ‘watery stuff’, we cannot say that something that feels like pain, but is not accompanied by the firing of C-fibres, is not pain, but ‘painy stuff’. According to Kripke, all it is for something to be pain is for it to feel like pain. Whereas the molecular structure of H₂O is essential to water, what is essential to pain is its subjective quality. Therefore, anything that feels like pain, such as this supposed ‘painy stuff’, is in fact pain, whereas anything which behaves like water, but is not composed of H₂O, cannot be water.

Conclusions

The above arguments reveal that the subjective quality of experience cannot be accounted for by the physical or functional accounts provided by the physical sciences. If we ask a physicist what orange light is, he or she will tell us that it is a transverse electromagnetic wave of a certain wavelength, or photons of a certain energy level. There is no mention here of the subjective quality of an orange experience. A biochemist could then tell us that when these photons hit one’s retina, a chemical reaction occurs in their photoreceptors. Once again, there is no mention of the subjective quality of an orange experience. If we then turn to a neurophysiologist, we will be told that the stimulation of one’s retina by orange light causes the propagation of electrical impulses down the optic nerve, resulting in the activation of certain neurones in the visual cortex. Again, the subjective quality of orange is left out of the account. Finally, if we were to speak to a psychologist, he or she could perhaps tell us that the activation of the visual cortex by orange light leads onto yet further processing, which accounts for one’s ability to discriminate orange and respond in appropriate ways to it.

From the above situations, we can see that while the physical information provided to us by science can tell us about the structure of orange light and the dynamics involved in its perception, it does not encapsulate the qualitative feel of an orange experience. So what is it that makes conscious experience so intractable to science? I argue that it is its first-person subjectivity. Of course, cognitive science is far from complete, but it is well understood, and the functional aspects of our minds, although technically impressive, pose few metaphysical problems. The phenomena of behaviour and the processes that drive it are complex physical mechanisms, but they are still physical mechanisms that are observable objectively in third-person, and thus can be accounted for with reference to more basic physical mechanisms.

Consciousness, however, is of an entirely different kind. It is not a third-person phenomenon, but a first-person phenomenon. Unlike physical mechanisms, subjective experiences cannot be observed objectively. As stated by philosopher John Searle (1992), each of us has “privileged access” to our experiences: a conscious experience is always someone’s conscious experience and only that person’s. Therefore, it is hardly surprising that objective information about neurones firing and proteins changing shape fail to encapsulate it. No matter how detailed our physical knowledge of the brain is, there will still always be that nagging question: why should all these physical processes be accompanied by subjective experience?

Of course, much can be and has been discovered about what neural mechanisms are correlated with qualitative experiences. For example, Francis Crick and Christof Koch (1990) have postulated that different modalities of perceptual information are bound and unified by 40-hertz oscillations in the visual cortex. Similarly, Gerald Edelman (1989) has proposed a way in which brain structures interact to allow the conceptual categorisation of perceptual signals before they contribute to memory. Furthermore, he links this to the generation of language by postulating links with Broca’s area and Wernicke’s area. Although these theories provide much valuable insight into the workings of the brain and how this relates to the functioning of our cognitive apparatus, they still fail to encapsulate the subjective quality of experience. At most, they propose brain structures and neural mechanisms which are correlated with subjective experience, but the qualitative nature of experience itself is eluded. The same question still remains: why are these processes accompanied by subjective experience at all? Over and above the physical facts about the brain, the existence of consciousness fundamentally remains an extra fact.

To many advocates of brain science, this conclusion may sound pessimistic, but I argue that it need not be interpreted this way. It does not say that we cannot eventually achieve complete physical knowledge about the brain, it does not undermine the potential usefulness of this knowledge in medical application, and it certainly does not require us to discard our current scientific theories. Rather, it simply suggests that the subjective aspect of the mind is beyond these theories.

In fact, upon closer analysis of the genesis of these theories, this is hardly surprising. In his essays on Mind and Matter (1967), the great physicist Erwin Schrödinger observed that our scientific knowledge “rests entirely on immediate sense perception”. In other words, theories are based on the observations we make in experiments, and these observations consist of sensual qualities: observations, after all, are our experiences. Therefore, since our theories arise from sensual qualities, they are in no position to explain these sensual qualities.

Indeed, this idea is well-established in philosophy, and in the attitudes of many scientists. Among the philosophers of mind who acknowledged this intangibility of the subjective, the most famous is perhaps Descartes, whose dualism suggested that consciousness is a separate fact from the physical. More contemporary thinkers, too, have embraced this idea: examples are the late neuroscientist John Eccles (1977) and the philosopher David Chalmers (1996). Although this metaphysics is highly speculative, it does at least accept the subjective as being another fact to consider over and above the structural and dynamical facts, and hence give it the recognition it deserves. After all, if what I want when I listen to my favourite Mozart symphonies is information about my neural processes, why don’t I just read a physiology textbook?

References

• Chalmers DJ (1996). The Conscious Mind: In Search of a Fundamental Theory. Oxford: Oxford University Press.
• Crick FHC, Koch C (1990). "Towards a Neurobiological Theory of Consciousness". Seminars in the Neurosciences, 2, 263-275.
  
• Descartes R (1642). Meditations on First Philosophy.
• Eccles JC, Popper KR (1977). The Self and its Brain. New York: Springer International.
• Edelman G (1989). The Remembered Present: A Biological Theory of Consciousness. New York: Basic Books.
  
• Jackson F (1982). "Epiphenomenal Qualia". Philosophical Quarterly, 32, 127-136.
• Kripke SA (1980). Naming and Necessity. Cambridge, Massachusetts: Harvard University Press.
• Levine J (1993). "On Leaving out what it's Like". In Davies and Humphreys (eds.), Consciousness: A Mind and Language Reader. Oxford: Blackwell.
  
• Locke J (1690). An Essay Concerning Human Understanding.
  
• Maung HH (2006). Consciousness: An Enquiry into the Metaphysics of the Self. Morrisville, North Carolina: Lulu Press.
• Nagel T (1986). The View from Nowhere. New York: Oxford University Press.
• Papineau D (2002). Thinking About Consciousness. Oxford: Oxford University Press.
  
• Polkinghorne J (1996). Beyond Science: The Wider Human Context. Cambridge: Cambridge University Press.
  
• Schrödinger E (1967). What is Life? and Mind and Matter. Cambridge: Cambridge University Press.
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