Explaining Nature: Aristotle on Induction
Forms of thinking that deserve to be called ‘philosophical’ can be found in ancient Chinese and Indian traditions,1 and include reflection on the natural world, and its significance for human beings.2 The discipline now known as ‘philosophy’, however, is generally agreed to have emerged in Greece during the fourth century bce, with the appearance of new forms of culturally located reasoning with the potential to transcend those specific historical contexts and constraints. While some locate the emergence of Greek philosophy in terms of the triumph of logos over muthos, others protest at the historical and intellectual simplifications attending this suggestion.3 Plato, for example, was certainly critical of older myths, but was perfectly capable of developing his own to advance his philosophical agendas.4
Others point to the importance of transcending local cultural and communal norms, moving away from solidarity towards objectivity through the recognition of something beyond a local frame of reference as the basis for truth. As Richard Rorty summarized Plato’s approach, ‘the way to transcend skepticism is to envisage a common goal of humanity – a goal set by human nature rather than by Greek culture.’5 To reason peri phuseōs (‘according to nature’) was to render oneself intellectually accountable to something beyond the local community and its norms.6
Our story begins with Aristotle’s scientific observations on the Aegean island of Lesbos, where he acquired an extraordinary knowledge of fishes and their behaviour around the Gulf of Kalloni, which was documented and analysed in his Historia Animalium.7 Aristotle argued that the complex observed patterns of the migratory movements of living creatures could be explained on the basis of a few general principles: the food supply, temperature changes, and issues related to breeding.8
Aristotle’s natural philosophy rests on the assumed capacity of the human mind to discern an existing, rather than imposed, order within the natural world, and the ability of human culture to offer analogies by which this may be explained and understood.9 This process of exploration was catalysed by a sense of wonder, which expands our intellectual and imaginative horizons.
It is through wonder that people now begin and originally began to philosophize; wondering in the first place at obvious perplexities, and then by gradual progression raised questions about greater questions, such as the phenomena of the moon and of the sun, about the stars and about the origin of the universe.10
Aristotle’s fascination with nature created a ‘drive to capture and recapture rhetorically that feeling of wonder (thaumazein) that is the origin and promise of all inquiry’.11
Aristotle was not the first thinker to advocate or undertake an investigation of the natural world. At the time, there already existed an established tradition of inquiry into nature, which is clearly delineated in by Plato in the Timaeus,12 even if it is imperfectly and incompletely developed (for example, Plato seems surprisingly uninterested in the non-human biological world). Aristotle’s agenda is broader, aiming to identify what is seen in the natural order, and how this may be accounted for. Aristotle does not use the term phusis to correspond to ‘nature’, as this term is now widely used, but to rather to designate the ‘nature [of things]’. The term kosmos began to be used from the sixth century to mean something like a ‘unified world order’,13 loosely corresponding to what is today designated ‘nature’.
As Aristotle conceives it, natural philosophy is an autonomous and self-contained discipline. In the Meteorology, natural philosophy is understood as a systematic inquiry into the different elements of the natural world, in order to discover the connections between its different parts, thus leading to an understanding of nature, which transcends a mere knowledge of nature.14 This idea is often linked with the notion of theōria—a mental beholding of the natural order. As this notion is important for the retrieval of natural philosophy, we shall consider it in some detail.
There is a growing recognition that a ‘novel and subversive claim’ can be seen as lying at the heart of the intellectual enterprises of both Plato and Aristotle: the belief that the ‘supreme form of wisdom is theōria, the rational “vision” of metaphysical truths’.15 The emergence of theōria as a means of articulating the task of philosophy and the status of its outcomes is an important staging-post in the narrative of the emergence of natural philosophy. It is important to note that this classical understanding of theōria was somewhat more sophisticated than some modern interpreters suggest—think, for example, of Martin Heidegger’s reduction of this notion to metaphysical optics.16 We begin by noting its cultural location, and then move on to consider its role in Plato, before turning to its implementation in Aristotle’s project of ‘theorizing’ the natural world.
While it is clearly problematic to define, or even describe, the nature of fourth-century Greek philosophy in terms of a transition from muthos to logos, there are good reasons for suggesting that a core task for the new cultural phenomenon of ‘philosophy’ was to defend the status of its claims to knowledge in the face of its rivals originating from religious or cultically privileged sources. The use of the term theōria had cultural overtones at this time, being linked with facilitating connections between individual Greek city-states and the broader Hellenic world through networks linking individuals and cults in different locations. A city—such as Athens—would participate in other Greek festivals and sanctuaries by sending delegates to witness the events in question.17 The idea of theōria as a ‘sacred beholding’ was particularly important in sustaining a shared religious practice across the Greek world—for example, in relation to the pronouncements of oracles.18
In the fourth century, Plato used the term theōria to characterize the role of the philosopher, speaking of a ‘mind habituated to thoughts of grandeur and the contemplation (theōria) of all time and all existence’.19 The bios theōretikos of a philosopher was not based on religious rituals or privileged oracles, but on the wise use of reason to discern and contemplate a grander vision of the world. The transfer of this notion of ‘contemplation’ from the religious or cultic domain to that of philosophy can be seen as intimating its oracular or revelatory status—and hence had a right to be considered as a public philosophy, not simply as a private persuasion or pursuit.20 ‘Plato identifies the philosopher as a new kind of theōros, an intellectual ambassador who makes a journey to a divine realm to see the spectacle of truth and then brings a report of his findings back home.’21
This view of the philosopher is set out in the allegory of the Cave, perhaps the best-known passage of Plato’s Republic, where the theme of a beholding of a grander reality that needs to be declared and enacted plays a critical role.22 For our purposes, the central narrative of the allegory is a group of people, entrapped within a dark cave, knowing only a world of shadows cast on its walls, who are unaware of a grander world beyond the cave. The philosopher is someone who has escaped from this intellectual bondage, and has seen the sunlit world beyond the cave—and thus, like a theōros, has a responsibility to bear witness to that world to those remaining within the cave, despite being overwhelmed by the enormity of this acquired vision of reality, and its obvious dissonance with the known and familiar world of the cave. For Plato, the philosopher is not primarily someone who has acquired a body of insight through teaching; rather, the philosopher has caught a vision of reality, or experienced a transformative beholding of the world.
Yet Plato has surprisingly little interest in the specifics of this world beyond the cave. The philosopher beholds this world, noting its ‘plants and animals and the light of the Sun’;23 yet Plato’s concern does not lie in reflecting on the natural world, but rather grasping and inhabiting the grander theōria that the escape from the cave makes possible. This becomes particularly clear in a brief discussion about looking at the stars. Glaucon believes this involves looking upwards; Socrates retorts that it means looking downwards, arguing that we should ‘behold (theōrein) with the mind, not with the eyes’.24 While Plato’s account of theōria deserves further elaboration,25 for our purposes there are two points that merit close attention. First, philosophy entails a new way of beholding reality, including the world of nature; and second, Plato does not appear to see this theōria as entailing or even encouraging a closer engagement with the world of nature. Aristotle concurs on the importance of theōria, but is willing to engage the natural world from its perspective, and to recognize the role of nature in developing theoretical perspectives. The process of engaging with the natural world, which is integral to Aristotle’s natural philosophy, particularly in dealing with questions such as the observation of change (kinēsis) or apparent goal-directed behaviour within nature, involves abstraction from the realm of nature to a realm of essences, which are clearly understood to be part of the natural world rather than belonging to some separate domain.
But what is the point of gaining such an understanding? What intellectual, moral, or practical benefits does it bring? How does it contribute to the pursuit of happiness or wellbeing (eudaimonia), which Aristotle commends as a human ideal? This is an important question, given the persistent anxiety within Aristotle scholarship that the pursuit of such theoretical knowledge might turn out to be pointless, or at least to be incompatible with Aristotle’s statements concerning a good life.26 Unlike some later theoreticians, Aristotle does not hold that theōria holds the key to mastering the natural world, allowing it to be transformed for the benefit of human beings. Contemplation may indeed be the ultimate goal of human rational action and reflection; yet it does not appear to serve any useful or productive purpose.27
This problem can be addressed in several ways. Perhaps the most satisfying would be to demonstrate that a closer reading of Aristotle’s works shows that theōria has a role that has hitherto been overlooked. Matthew Walker, for example, develops an interesting argument to this effect, picking up on Aristotle’s maxim that ‘nature does nothing in vain’. If this is indeed the case, then there must be some reason for, and benefit from, the human desire to understand our world.28
An alternative approach is to locate theōria within a wider interpretative framework, arguing that the reflective beholding of the natural world serves a deeper telos that lies beyond the scope of Aristotle’s system. Perhaps the most significant development of this approach lies in early Christian theology, which held that the ‘beholding’ of the natural world was religiously significant, in that it was an indirect beholding of God, thus facilitating both an understanding of reality and appropriate forms of worship.29 Any perceived inadequacy in Aristotle’s approach was thus remedied by a Christian expansion of his understanding of the theoretical beholding of nature to embrace a theoretical beholding of God’s work of creation, which exhibited the wisdom and order of its creator.30 This, of course, raises the important question of the interface between a natural philosophy and a natural theology, to which we shall return at several points in this work.31
One of the most interesting aspects of Aristotle’s natural philosophy is his attentiveness to observing natural entities—such as plants, animals, and stars. Perhaps the best-known statement of this observational respectfulness is found in the opening lines of Book VII of his Ethics:32
We must, as in all other cases, set the observed facts (phainomena) before us and, after first discussing the difficulties (diaporēsantas), go on to prove, if possible, the truth of all the common opinions about these affections of the mind, or, failing this, of the greater number and the most authoritative; for if we both refute the objections and leave the common opinions (endoxa) undisturbed, we shall have proved the case sufficiently.
The Greek phrase sōzein ta phainomena, best translated as ‘saving the appearances (or phenomena)’, is often used to designate this respect for observation, and is variously and vaguely attributed to both Plato and Aristotle.33 In fact, the Greek phrase sōzein ta phainomena, popularized by Pierre Duhem in the first decade of the twentieth century, is more characteristic of later commentators rather than of Aristotle himself. It is difficult to translate the phrase into English, in that the Greek term phainomena resists easy renderings, such as ‘appearances’, ‘observations’, or ‘observed facts’.34 This phrase now tends to be associated with an instrumentalist understanding of scientific theory, which holds that a theory capable of accommodating existing observations is not necessarily true, in the sense of somehow ‘corresponding’ to reality.35
While this principle of respecting phenomena is not explicitly stated in Aristotle’s writings using this phrase, the idea itself is clearly present. Both science and scientific explanation—as Aristotle understands these—are to be construed realistically, in that science must mirror reality, and therefore theory always must cohere with observation and empirical investigation.36 It is, however, innocent of the instrumentalist associations that later came to be associated with the phrase, even if it can be argued to be consistent with them. Aristotle is concerned with the identification of the archē or archai—the ‘first principles’ that lie behind what is observed in natural phenomena and living beings. He clearly considers these to have a real existence independent of these phenomena, which underlies their explanatory capacity in relation to those phenomena.37 Aristotle’s persistent emphasis on the importance of observation of nature may occasionally lead him to some false conclusions (such as the highly influential theory of spontaneous generation);38 nevertheless, his empirical instincts must be acknowledged.
Yet Aristotle is not entirely consistent here. As Eckard Kessler points out, there is an apparent (and important) methodological pluralism within Aristotle’s writings on natural philosophy concerning the identity of natural entities: a largely non-empirical metaphysical approach (found in the Physics), and the more empirical approach found in On Generation and Corruption and the Meteorology.39 This led to the emergence of tensions in the later Renaissance between metaphysical and empirical approaches to natural knowledge. The emergence of a ‘strong naturalistic tendency as early as the beginning of the sixteenth century’ does not need to be seen as a rejection of Aristotle, but can rather be seen as a methodological refocusing within the Aristotelian corpus.40
In the end, the empirical method won out, mainly because it proved capable of dealing with questions that simply could not be resolved by an appeal to first principles. Ptolemy’s geocentric view of the solar system, though arguably based on the best observational evidence of his age,41 had to give way to the heliocentric systems of Kepler and Galileo, because of the observational evidence that could not adequately be accommodated by the older theory.42 Yet the empirical method would undergo significant development in the early modern period, partly through the rise of the experimental method, and partly through the use of instruments such as microscopes and telescopes, which extended the capacity for both observation and measurement, and in doing so, undermined some of the more questionable aspects of Aristotle’s natural philosophy.
Aristotle’s own specific ways of making sense of the natural world reflect the limiting conditions of his historical and cultural location. It is not difficult to identify what appear to be errors of judgement on Aristotle’s part,43 some of which became petrified as he came to be regarded as an ‘authority’ in Renaissance science. For example, in On the Parts of Animals, Aristotle remarked that a philosopher could take pleasure in contemplating ‘things constituted by nature’ kata theōrian, including both the ‘ungenerated, imperishable, and eternal’ phenomena of the heavens and the generated and changeable realities of the world.44 Yet this absolute distinction between the changing ‘sub-lunar’ world and the perfect, regular, and unchanging ‘celestial’ realm caused his later interpreters some difficulties. Tycho Brahe’s observation of the appearance of a bright new star in the constellation of Cassiopeia in November 1572, and Christopher Scheiner’s observation of sunspots in 1611,45 both suggested that the celestial realm was subject to imperfection and change.
This discussion, however, lay in the future. Our concern now focuses on what Aristotle appears to have understood by the ‘explanation’ of nature.
So what does Aristotle understand by explaining nature? We have already noted the importance of identifying ‘first principles (archai)’ underlying the phenomena of the natural world. Aristotle’s natural inclination is to turn to teleology as an explanatory framework.
Teleological explanations are a central feature of Aristotle’s investigation of nature and reflect the importance he attributes to final causality in the coming to be and presence of regular natural phenomena. In Aristotle’s view of the world, everything that exists or comes to be “by nature” comes to be or changes, unless prevented, for a purpose and towards an end, and is present for the sake of that purpose or end.46
As is well known, Aristotle identifies four causes which may be discerned as underlying phenomena in the world or human culture—such as the creation of a bronze statue:47 a material cause; a formal cause; an efficient cause; and a final cause. In the cause of a bronze statue, the efficient cause (or principle that produces the statue) is the art (technē) of bronze-casting the statue.48
This raises a difficulty that has long been recognized in Aristotle’s approach: the assumed analogy between the causal processes that generate natural and cultural entities.49 It is quite easy to point to the causal processes that underlie the production of a cultural artefact, such as a bronze statue. Yet the unevidenced assumption that such causal processes also underlie the generation of natural entities, such as plants and animals, is deeply problematic. Aristotle in effect speaks of each internal causality within nature as an ‘artist (demiourgos)’.50 Furthermore, there are points in Aristotle’s scientific reflections, particularly in trying to understand the structures of plants and animals, when certain non-empirical grounding assumptions are brought into play, including the belief that ‘nature does nothing in vain’.51
Although there are clear parallels between Aristotle’s understanding of ‘science (epistēmē)’ and that of Plato,52 there are significant points of divergence, generally reflecting Aristotle’s adaptation of Plato’s approach to enable an engagement with the phenomena of the natural world. Perhaps the most important is Aristotle’s use of the process of induction (epagōgē) in engaging with these phenomena.53 For Aristotle, scientific knowledge is based on an empirical apprehension of particulars, which requires an inductive method of investigation.
At several points, Aristotle defines epagōgē in terms of ‘proceeding from particulars up to a universal’,54 which he often contrasts with sullogismos (‘deduction’), in which the reasoning process begins from established universals. This, of course, raises questions about imperfect inductive generalizations,55 and whether such generalizations can really be considered as epistēmē rather than simply doxa. One important (and influential) outcome of the application of this form of reasoning within Aristotle’s writings concerns the eternity of the world. This belief is clearly not an empirical observation in itself; it is a view that is based on Aristotle’s understanding of the relation of matter and forms, neither of which are empirical notions.56 As the subsequent discussion of this issue made clear, Aristotle’s arguments for the eternity of the world proved vulnerable.57 The ‘eternity of the world’ was doxa, rather than epistēmē.
The debate about the correct interpretation of Aristotle’s notion of epagōgē and its relevance for a natural philosophy continues. I shall note two significant engagements with Aristotle’s account by leading philosophers of science, noting how both found Aristotle profitable yet underdeveloped on this point. In both cases, a strong case can be made for asserting that these are legitimate readings of Aristotle’s concept of epagōgē and its associated methods for studying the natural world, which are defensible alternatives to the ‘standard’ reading of Aristotle at this point.58
The Victorian philosopher William Whewell (1794–1866) held that Aristotle anticipated his own view that induction involves not only the accumulation and generalization of facts, but also the discovery of new concepts through a process of active interpretation of the natural world.59 For Whewell, induction was a process of reflection that added something essential to what was otherwise simply a process of enumeration. ‘There is a New Element added to the combination [of instances] by the very act of thought by which they were combined.’60 Whewell’s main criticism of Aristotle was that he failed to give adequate attention to the need to ‘introduce’ new ideas or concepts that were ‘distinct from sensation’61—such as some kind of ‘organizing principle’, which was integral to the process of scientific explanation.
The American philosopher Charles S. Peirce (1839–1914) is noted for his development of ‘abductive’ modes of thought in making sense of the natural world. While much attention has been given to the specifics of this ‘creative act of making up explanatory hypotheses’,62 which is now widely referenced within the philosophy of science, not enough attention has been given to its origins in Aristotle.63 Peirce himself held that the origins of his abductive method lay in his reading of Prior Analytics II.25, which he considered to be defective as it stood, yet generative in terms of the possibilities that it suggested. Although Peirce’s reconstruction of Aristotle’s argument is open to criticism at points,64 it is clearly a legitimate interpretation and extension of his approach.
For example, it could be argued that the Posterior Analytics suggests that Aristotle is feeling his way towards offering what is essentially a psychological description of the mental process of grasping of a universal form in particular cases through ‘intuitive induction’ or intuitive reason.65 Even the ‘standard’ reading of Aristotle concedes the imaginative or intuitive elements in his account of induction: it is ‘a process not of reasoning, but of direct insight, mediated psychologically by a review of particular instances’.66 In an early lecture, Peirce described abduction as
that process in which the mind goes over all the facts the case, absorbs them, digests them, sleeps over them, assimilates them, dreams of them, and finally is prompted to deliver them in a form, which, if it adds something to them, does so only because the addition serves to render intelligible what without it, is unintelligible.67
This brief discussion of Aristotle’s natural philosophy sets the scene for its later development. The full story of how Aristotle’s natural philosophy was favourably received within the Islamic world,68 before coming to be rediscovered and reappropriated in western Europe, is fascinating, and still not fully understood. How, for example, did Aristotle’s views on astronomy, supposedly empirical in their foundations, come to be received as authoritative in European universities, thus causing such difficulties for empirical innovators such as Galileo? Although these are important historical questions, they are not all relevant for our purposes.
The most appropriate point at which to reconnect with the western tradition of natural philosophy is in the thirteenth century, when this discipline emerged as a distinct and potentially autonomous field of inquiry, which would gradually loosen its connections with Aristotle and his commentators, in favour of a more explicitly empirical approach.