Introduction: Why Science Wars?
Can human beings know anything, and if so, what and how? This question is really the most essentially philosophical of all questions.
(Bertrand Russell)1
Doesn't all science live on this paradoxical slope to which it is doomed by the evanescence of its object in its very apprehension, and by the pitiless reversal that the dead object exerts on it? (Jean Baudrillard)2
What do scientists know and how do they know it? Straightforward questions, surely, and important ones, yet over the four hundred–year history of modern science, no answers have stood up to critical scrutiny.
No theory of how science works—no philosophy of science—has won universal acceptance. Scientists typically describe their work as producing objective knowledge of reality, knowledge that is, if not certainly true, then converging on it. Critics argue that what scientists call knowledge is actually pragmatically justified, probabilistic, subjective interpretations of experience. This may seem an abstract intellectual issue, but it is not.
Over the past two hundred years, society has become increasingly dependent on science-related technologies and the practice of science has become deeply embedded in social, political and economic institutions. Ambiguity about the nature of scientific knowledge thus has profound implications for the role of science in society, especially in the formulation of effective science-relevant public policies. The need for such policies is of particular moment today, relating, among other issues, to pandemics, global warming, energy alternatives, environmental degradation, and commercial applications of increasingly powerful biotechnologies, nanotechnologies, robotics, and artificial intelligence software.
For their part, scientists argue that policy decisions in these areas must be determined based on scientific knowledge because it is objective, hence value neutral. If this argument is contested, however, on the grounds that scientific knowledge is not objective, that it is itself political because it is a
product of value judgments by members of an elite community, then science cannot be the neutral arbiter of controversial sociopolitical action agendas. Furthermore, if scientific theories are not true in the sense of corresponding to reality, that strengthens the demands of religious fundamentalists for the inclusion in science education of what the fundamentalists believe to be true about reality.
In this book, I argue that an understanding of how scientists produce knowledge has proven elusive because there is a logical inconsistency at the heart of modern science. Modern science is based on a conflation of deduction and induction, rationalism and empiricism, realism and conventionalism. The self-proclaimed goal of modern science from its beginning has been to use experience to transcend experience and reveal the mind-independent causes of experience. This cannot be done logically, but success is routinely proclaimed based on experimental confirmations of theory-based predictions, thereby proving the reality of scientific objects. I will argue that the contradiction at the heart of modern science is the result of equivocation over how the word “knowledge” is to be defined. This is pivotal because the definition of “knowledge” affects what “truth,” “rationality,” and “reality” mean.
Words matter. They matter because words often carry connotations, presuppositions and value judgments that shape how we respond to them. Consciously and unconsciously, we respond very differently to “knowledge” than we do to “belief” and “opinion.” We use each of these words intending that they have different effects on listeners and readers. A scientific conviction typically is characterized as a matter of knowledge, while a religious conviction typically is characterized as a matter of belief and a political conviction as a matter of opinion. To claim to know something, especially to know something scientifically, is taken by just about everyone to be a fundamentally different kind of claim from stating opinions or beliefs about those same matters. “Knowledge” has more rhetorical force than the words “belief” and “opinion.” Why is that?
Knowledge trumps belief and opinion because “knowledge” carries the connotation of a correlation with truth, and through truth with reality, with the way things “really” are regardless of beliefs and opinions. This elevates knowledge above belief and opinion, and it elevates people who possess knowledge, or can successfully claim to possess it, above those who “merely” express opinions and beliefs. Allowing the word “knowledge” this privileged usage implicitly assumes that knowledge really is essentially different from beliefs and opinions, but is this assumption justified? We can choose to define “knowledge” as statements that are necessarily true while opinions and beliefs may be false. But we could also choose to define “knowledge” as those
opinions and beliefs for whose truth convincing but not compelling reasons can be given. In the latter case, “knowledge” would lose some of its rhetorical force because it, too, might be false and because what seems a convincing reason to one person might not be convincing to another.
From the time of the pre-Socratic Greek philosophers in the fifth century bce to the present, the dominant definition of “knowledge” in Western culture makes knowledge fundamentally different from opinion and belief. On this view, there is only one truth of any matter and that is known only to the people who possess knowledge. I will call this definition of “knowledge” knowledge in the strong sense. A rival definition, also proposed in the preSocratic period, was that “knowledge” was a name for opinions and beliefs for whose truth more or less good reasons could be given, but never with certainty. I will call this definition of “knowledge” knowledge in the weak sense. Since 1600, natural philosophy, now called modern science, has promoted itself as the only source of knowledge for human beings. The historian Stephen Gaukroger began his history of the cultural context out of which modern science emerged as follows: “One of the most distinctive features of the emergence of a scientific culture in modern Europe is the gradual assimilation of all cognitive values to scientific ones.”3 Only scientists possess knowledge, only scientists possess truth, only scientific reasoning is rational, and only scientists possess an understanding of reality. This poses a profound challenge to all other responses to human experience, to art and literature, for example, no less than to religion and philosophy.
Given what is at stake, what is the correct definition of “knowledge”? Is knowledge fundamentally different from opinion and belief? Attempts to answer this question bump up against the fact that there is no Absolute Dictionary in which to look up the correct meaning of words. There is no uniquely correct meaning of a word because what words mean is a function of how people choose to use them. People routinely claim to have knowledge about matters that concern us, matters about which there are diverse opinions and beliefs. How can we be sure that their knowledge claims are valid, requiring that we give up our opinions and beliefs about those matters? How can we be sure that people are not just using the “knowledge” word in order to intimidate us into giving up our opinions and beliefs in favor of what are, in the end, only their opinions and beliefs? For that matter, how do we know that there actually is such a thing as knowledge in the strong sense, statements about the world, for example, that are necessarily true? Perhaps knowledge is not something universal and objective that transcends opinion and belief, but just those opinions and beliefs that are most strongly held in a given community at a particular time.
The question of whether knowledge of the world is possible cannot be answered without first settling what “knowledge” means in science. This will then determine what “objectivity,” “truth,” “reality,” and “rationality” mean; it also affects what the object of scientific knowledge is. What is scientific knowledge, knowledge of? This relates to what scientists mean by “the world” and “nature.” Do “world” and “nature” refer to that which is independent of human experience and reasoning, or to some conventionally conceptualized aspect of human experience? The definition we choose for “the world” makes a major difference to what we mean by knowledge of the world and to the criteria by which we justify claims of knowledge of the world, as opposed to having opinions or beliefs about the world. All of these questions place the word “knowledge” precisely at what the author Alex Rose called the “mysterious intersection of epistemology and ontology.” At this intersection, our conceptions of knowledge and reality become mutually implicating. A commitment to knowledge as necessary truth, for example, implies a deterministic metaphysics in which time is an illusion: everything that happens in time is already implicit in the beginning. A commitment to knowledge as contingent truth, on the other hand, implies an evolutionary metaphysics in which time is real, a name for the emergence of unpredictable happenings. The intersection of epistemology and ontology is thus the intersection of our conceptions of knowing and of being.
Knowing is a process in the human mind, while being is the most universal feature of a reality conceived to be wholly independent of human experience. How can knowing say something about what is independent of our conceiving and our saying? There is an issue here of the most profound importance for any discussion of truth, rationality, and reality. Can the mind reason about the world in a way that transcends its biology and its socialized experience, allowing it to know a mind-independent reality? Is a knowable, mindindependent reality just an idea of ours?
The problem of defining a cluster of words cognate with the word “knowledge” is central to any understanding of science as knowledge of the world. Natural scientists routinely claim that their accounts of the world tell us what is real and what is not real, how the world works, and what it is reasonable to say about the world. Such accounts, if they are valid, surely deserve to be called knowledge, not opinions, but how can we know that they are valid? When scientists use the term “knowledge” do they mean it in the strong sense such that scientific knowledge claims are objective and accounts of reality, or in the weak sense, in which case they are inter-subjective and accounts of human experience only? The unhelpful answer given by scientists, as attested by the history and philosophy of modern science, is “Both”!
Since the mid-nineteenth century, growth in the explanatory scope, predictive success, and practical applications of scientific theories have been awe inspiring. This makes a strong pragmatic case that claims for the truth of such theories are far more than just the opinions and beliefs of the scientific communities that hold them. Through its association with technologies that have literally transformed the conditions of human existence, the idea of science has become deeply entrenched in contemporary social institutions and individual consciousness. This reinforces the prevailing identification of science with knowledge of the world as it really is. Social processes, including the way science is taught at all levels and how it is presented to the public, reinforce the claim that scientists possess objective knowledge of reality rather than empirically justified opinions and beliefs about experience. But how can this claim be verified, given that the human mind has no access to such a reality except through individual and collective experience, which science tells us is totally different from the way things “really” are?
Can scientists claim to know reality because their theories provide satisfying explanations of experience, make correct predictions, and give us a measure of (technological) control over experience? Logically, and historically, the answer is “No.” Even all three of these accomplishments together do not provide proof that a theory is either about a mind-independent reality or that it is fundamentally different from opinion and belief. The history of science shows that theories that we now consider wrong were once considered true precisely because, for some period of time, they provided satisfying explanations, made correct predictions, and enabled new technologies. This suggests that current theories, as new experiences accumulate, also will be replaced by newer theories as all previous theories have been. And with their replacement, may not new realities be proclaimed (created?), as has been the case repeatedly since modern science emerged?
Any claim to universal and certain knowledge of reality is also belied by the nature of logical reasoning. Since the nineteenth century an increasingly strong consensus has grown among logicians, mathematicians, and philosophers that logical reasoning cannot prove the existence outside the mind of the conclusions of even the most rigorous of deductive arguments. All that such arguments can do is establish the logically necessary truth of their conclusions given the certain truth of their premises together with the truth of all the definitions, axioms, and postulates on which these premises ultimately depend. To avoid an infinite regress, however, the truth of these definitions, axioms and postulates must be stipulated or claimed to be self- evident, on nonlogical and non- empirical grounds.
All this suggests that knowledge in science cannot mean knowledge in the strong sense, but only knowledge in the weak sense: contextually justifiable opinions and beliefs. But how can successful explanation, prediction and control just be educated opinion, “miraculously” correlated only with human experience and not with the real underlying causes of experience? Isn’t it reasonable to claim that our theories are at least converging on a definitive account of reality and thus in principle at least are knowledge in the strong sense?
The approach adopted in this book to answering the question of what scientists know and how they know it is historical. Its chapters trace changing conceptions of and controversies over what scientific knowledge is, what it is about, and how it is acquired, from the seventeenth century rise of modern science through the twentieth century. A historical approach allows us to watch unfold within the evolving practice of science a recognition that the nature of scientific knowledge is problematic by way of repeated attempts to clarify it. What we also see by adopting a historical approach is the persistence over centuries of opposing solutions to the problem of knowledge in general and of scientific knowledge in particular. This persistence itself calls into question any simplistic account of science as a progressive revelation of reality.
The first chapter locates modern science’s conflicted conception of knowledge in a “perpetual battle” that has been raging for some twenty-five hundred years among Western philosophers over the meanings of “knowledge,” “truth,” “reality,” and “rationality.” Chapters 2–4 describe the very different conceptions of scientific knowledge promoted by prominent founders of modern science: Francis Bacon, Rene Descartes and Galileo Galilei, Christian Huygens, Isaac Newton, and Gottfried Wilhelm Leibniz.
Chapter 5 describes philosophical responses to the knowledge problem that were accommodated to the emergence of modern science, from Hobbes to Kant, while Chapter 6 describes the impact of modern science on eighteenthcentury European intellectuals, leading to the creation of the social sciences, the proclamation of an Age of Reason, and proposals for social reform.
Chapters 7–9 describe nineteenth-century science, philosophy of science, and the Romantic reaction against both modern science and the science-based apotheosis of reason inherited from the eighteenth century. Chapters 10–16 range over twentieth-century defenses of, and attacks on, science as producing objective knowledge of the world, the openly proclaimed “Science Wars” of the closing decades of the century, and the implications of equivocation over the meaning of “knowledge” in science for society and for formulating public policies.
Knowledge as a Problem
The knowledge problem was born with Western philosophy, and like Jacob and Esau wrestling for primacy in their mother’s womb, it was born into conflict.
Early in Greek philosophy, circa 475 bce, Parmenides of Elea contrasted two irreconcilable approaches to knowledge. As laid down in his work On Nature, there was the way leading to logically necessary truth, his way of course, and then there was the way of mere opinion, the way taken by his misguided contemporary, Heraclitus. A century or so later Plato used this contrast to distinguish philosophers, lovers of wisdom who seek truth about a changeless reality, from sophists, who settle for opinions about an endlessly changing experience.
The Sophist is a Platonic dialogue dominated not by Socrates, but by an unnamed philosopher from Elea who is visiting Athens. To make the connection with Parmenides still clearer, Plato has the visitor declare that Parmenides is his [philosophical] “father.” In the course of the dialogue, the visitor expounds Plato’s version of Parmenides’ deductive logic–driven philosophy and contrasts it with the teachings of sophists, pretend philosophers. At one point, the visitor describes the relationship between philosophers and sophists as “a sort of Battle of Gods and Giants because of the dispute they have with each other about [the nature of] beinghood [reality].”1
The Giants, with whom the sophists are allied,
drag all things down out of the heavens and the invisible realm, literally grabbing rocks and trees with their hands. They grasp all such things and maintain strenuously that that alone is [has being and thus is real] which allows for some touching and embracing. For they mark off beinghood [reality] and body [materiality] as the same; and if anyone from the other side says that something is [real] that has no body, they despise him totally and don’t want to listen to anything else.2
The Giants, in short, are empiricists, identifying reality with the material world of ordinary human experience.
The philosophers, allies of the Gods,
defend themselves [against the Giants] very cautiously out of some invisible place on high, forcing true beinghood to be certain thought-things and disembodied forms. But the bodies [the material objects] of their opponents and what these men call truth, they bust up into small pieces in their arguments and call it, instead of beinghood, some sort of swept-along becoming.3
The Gods are rationalists for whom reality is immaterial, is unchanging, and transcends human experience.
“And between these two, Theaetetus, a tremendous sort of battle over these things has forever been joined” [my italics],4 a battle between two irreconcilable conceptions of reality, knowledge, and our ability to know truths about reality. Such truths lie at the intersection of ontology and epistemology, which is “mysterious” if it is claimed that the mind can know what is independent of the mind. How “real” is defined implicates the knowability of the real, and how “knowledge” is defined implicates what is real. For Plato, nothing less can be the object of philosophy than seeking universal, necessary, and certain knowledge of reality, defined as that which exists external to and independent of the human mind. Reality is analogous to mathematical objects—triangles, circles, spheres—which are eternal, immaterial, and changeless. Like knowledge of mathematics, knowledge of reality can be known only by a properly reasoning mind.
In the dialogue Phaedrus, Plato has Socrates say that “the reality with which true knowledge is concerned, [is] a reality . . . intangible but utterly real, apprehensible only by the intellect,” without any involvement of the body and its empirical experience. Because the Gods in their “heavens” are detached from all materiality, they are able to see
absolute justice and discipline and knowledge, not the knowledge which is attached to things which come into being [and pass away], nor the knowledge which varies with the objects which we [based on our empirical experience] now call real, but the absolute knowledge which corresponds to what is absolutely real in the fullest sense.5
To the extent that the mind is able to rise above the body and its material experiences, it can “see” absolute knowledge of the real as the Gods do, and this is the goal of the philosopher. In the dialogue Theaetetus, which has as its subject the nature of knowledge, Socrates says that the senses give us empirical experience of a relentlessly changing natural world. Nature is a world of becoming and thus cannot be an object of certain knowledge, only of probable opinion and belief. But the mind, Socrates insists, perceives “through its
own instrumentality,”6 with no involvement of the body and its senses, that which makes unchanging knowledge possible because its object—echoing Parmenides—is the world of changeless Being.
The Theaetetus appears to end inconclusively, with Socrates agreeing that defining “knowledge” as “true opinions with a reason” comes closest to what knowledge is. However, what Plato means here by “a reason” is a deductive logical demonstration, and it is this that transforms true opinions into knowledge in the strong sense. In the Meno, Socrates says that
true opinions are a fine thing and do all sorts of good so long as they stay in their place, but they will not stay [there] long. They run away from a man’s mind, so they are not worth much until you tether them by working out the reason [why they are necessarily true] . . . once they are tied down they become knowledge.7
For Plato, truth is identified with knowledge in the strong sense: it is universal, necessary, and certain. Knowledge “does not reside in the sense impressions but in our reflection upon them.”8 This “reflection” is a distinctive way of reasoning that is the hallmark of the true philosopher. Plato calls it dialectical reasoning, and it alone is capable of grasping universal, necessary, and certain truths about reality.9 The dialectical reasoner, “applying his pure unadulterated thought to the pure and unadulterated [wholly ideal] object” rises above hypotheses and assumptions and making “no use whatsoever of any objects of sense, but only of pure ideas” moves on “through ideas to ideas and ending with ideas.”10 The mind, from within itself, has the ability to comprehend reality, independently of the body and its experience of the material world to which the body, but not the mind, belongs. Mathematics, for Plato, comes very close to exemplifying knowledge in the form of ‘ideas about ideas ending in ideas.’ Mathematics gives us universal, necessary, and certain knowledge because it uses deductive reasoning only, and mathematical objects are eternal and changeless. Where mathematics falls short is in its dependence on diagrams for geometric proofs and on hypotheses whose necessary truth is left as self-evident, not explained. For Plato, there is a slightly higher form of knowledge that the human mind can attain than mathematical knowledge, knowledge that is wholly ideal, the product of “pure” intellection.11
Because of the way that Plato defined “reality,” and coordinately “knowledge,” “truth,” and “rationality,” there can be no knowledge of nature because nature is constantly changing. To claim knowledge of something that is always becoming something else is self-contradictory. Knowledge can only have the changeless as its object, and it is the philosopher’s ability to transcend
sense-based experience and apprehend truths about changeless being that makes universal, necessary, and certain knowledge of reality possible. We can have more or less useful opinions and beliefs about the natural world, but not knowledge.
Aristotle was in full agreement with Plato that only what was necessarily true and “could not be otherwise” can be called knowledge. “What is understandable and understanding,” he wrote in his Posterior Analytics, “differ from what is opinable and opinion because understanding is universal and through necessities, and what is necessary cannot be otherwise.”12 By contrast, opinion “is about what is true or false, but can also be otherwise.”13 In the Nicomachean Ethics he wrote: “We all suppose that what we know is not capable of being otherwise . . . Therefore the object of knowledge is of necessity . . . Therefore it is eternal . . . and things that are eternal are ungenerated and imperishable.”14
Aristotle was in full disagreement with Plato, however, on changeless immaterial Being as the only possible object of knowledge. For Aristotle, reality was the ever-becoming material world that Plato dismissed as unreal and unknowable. “The most paradoxical thing of all,” Aristotle claimed, “is the statement that there are certain things besides those in the material universe, and that these are the same as sensible things except that they are eternal while the latter are perishable.”15 Reality, for Aristotle, is the sum total of all of the particular material objects “out there” beyond the mind, and nothing else. Everything that the human mind knows about this reality begins with sense experience of individual material objects. Knowledge of nature in the strong sense is nevertheless possible because the human mind is able to acquire directly from its experience of individuals the universal truths that are required for reasoning deductively about the world.16
It is crucial for an understanding of Aristotle’s position, and of modern scientific reasoning as well, to appreciate how different inductive and deductive reasoning are.
In a deductive argument, if the premises are true, then the conclusion must be true; the truth of the conclusion follows necessarily from the truth of the premises. But a deductive argument requires that at least one of its premises be a universal statement that is known to be true or is taken to be true hypothetically. If we accept as true that ‘All men are mortal’ and accept also that ‘Socrates is a man,’ then it must be true that ‘Socrates is mortal.’ If we accept that Euclid’s definitions, axioms, and postulates are self-evidently true, then all of the hundreds of theorems of Euclid’s geometry are necessarily true because they are deduced from true premises. Note that to reason deductively about the world, which Aristotle said was possible, we would have to know the truth of some universal statements about the world. But Aristotle held that all
our knowledge of the world comes from sense experience, which is always of individuals, never of universals, so how can we know the truth of universal statements about the world?
By contrast with deduction, in an inductive argument, even if all the premises are true the conclusion can still be false. Even if every reported sighting of a swan by European observers for over thousands years was of a white swan, it is not necessarily true that all swans are white. Based on the evidence available for all that time, it was a valid inductive inference from experience that all swans are white, and a very reasonable generalization, but it turned out to be false when in 1697 the Dutch explorer Willem de Vlamingh discovered black swans in Australia. A crucial point to keep in mind throughout this book is that nothing can be deduced from particular observations, no matter how numerous. More or less probably true inductive generalizations can be drawn from observations, but no necessary truths, as required by knowledge in the strong sense.
We are free to assume that some universal statements about nature—the conservation of matter and energy, definitions of space and time—are true in order to allow reasoning about nature deductively. We might do this in order to draw deductive inferences from them and then compare those inferences to experiential facts, a strategy that became and remains central to modern science. In this way, the gulf between induction and deduction seems to be bridged, but it is hypothetical only, contingent upon the assumed truth of universal statements based on generalizations from experience. It is really inductive reasoning disguised as deductive reasoning because the truth of the assumptions is just that: assumed. How, then, could Aristotle claim that deductive knowledge of nature was possible if he also held that all knowledge of nature begins with sense experience of particulars?
The answer for Aristotle was that universals existed outside the mind, but only in individual material objects, not independent of material objects as they were for Plato. Individual objects somehow embodied the universals of which they were individual exemplifications, so universals were really “out there,” not just conventional group names. That is the ontological part of Aristotle’s solution to the problem of universals. The epistemological solution is his claim that the human mind possessed a special mental faculty that he called the active, or agent, intellect. This enabled our minds to recognize the universals that are in individuals, to “see” in an individual dog the universal dog, its variety, species, and genus, for example. Through the operation of the active intellect, universals “come to rest in the soul [mind].”17 We know their truth directly without further need of logical demonstration.
The universal “first principles” required for deductive reasoning of any kind are somehow arrived at non-inferentially from our experience of the world of particular objects.18 According to Aristotle, the mind also possesses an intuitive faculty that allows it to recognize the self-evident truth of first principles that allows deductive reasoning to begin.19 These first principles were analogous to the purportedly self-evident truths on which Euclid based his deductive formulation of geometry. At least in principle, therefore, natural scientific knowledge in the strong sense was possible for the human mind, just as knowledge in mathematics was, because in both cases it comprised deductions about objects that were changeless and eternal (though mathematics played only a limited role in Aristotelian natural science).20
For Plato, for Aristotle, and for all the later philosophers who allied themselves with the Gods—all the rationalist and idealist philosophers who have dominated the Western philosophical tradition—the mind knows some universal truths and therefore can acquire, through deductive reasoning, knowledge that is universal, necessary, and certain. As the human mind cannot know the necessary truth of statements about reality from empirical experience—that would require an inductive generalization and result in probable knowledge only—the human mind must know some truths a priori or it could never begin to reason deductively. How does it know them?
Plato proposed, perhaps only half-seriously, that knowledge in the strong sense was possible because the mind could remember truths about reality that it had “seen” while it lived with the Gods, before it was born into a body. Aristotle proposed a mental faculty that grasped universals in the particulars of empirical experience together with an ability of the mind to intuit the truth of non-demonstrable first principles of reasoning. Augustine proposed that God gave humans selective access to His mind and thereby to the universals in it. Most medieval Muslim and Christian philosophers adopted some version of Aristotle’s view; some adopted a version of Augustine’s. Descartes proposed that the mind possessed innate ideas and an intuitive ability, a “natural light,” to recognize truth. Kant created a philosophical system in which the mind itself generates necessary truths about experience.
The allies of the Giants, the sophists, that Plato and Aristotle took most seriously included Protagoras, Gorgias, and Antiphon. These were prominent Greek thinkers to whom Plato denied the title “philosopher,” stigmatizing them as second-rate thinkers, fee-seeking teachers of rhetorical tricks who claimed to possess knowledge but didn’t. It is a cliché that the winners get to write the history books, and that applies as much to intellectual history as to social, political, and military history. The teachings of Protagoras and Gorgias were derided by Plato, dismissed by Aristotle, and parodied by
both. As few of the writings of the sophists have survived intact, much of what we know of their ideas is from quotation and discussion by other, often hostile, authors. Nevertheless, surviving texts and scholarly reconstruction show that Protagoras and Gorgias, and at least some of their fellow sophists, among them Antiphon, had carefully thought-out positions on knowledge, truth, reality, and rationality.21
Protagoras is most famous for a statement that could also be the motto for everyone on the side of the Giants, from antiquity to the present. It is typically translated as ‘Man is the measure of all things.’ Plato and Aristotle mocked this as entailing that knowledge, truth, and reality were all subjective. They claimed that Protagoras’ statement meant that what appeared to be true for each individual was true, for that individual, and that what appeared to be real for each individual was real, for that individual. It followed, nonsensically to Plato and Aristotle, that there was no such thing as objective knowledge, no such thing as supra-individual truths, and no shared conception of reality.22
It is pretty clear that Protagoras did not mean by ‘Man is the measure of all things’ what Plato and Aristotle said he meant: that all claims to knowledge and truth are incorrigibly relative to each individual. Rather, Protagoras seems to have meant that humans are the measurers of all things. All of the measures by which we order our experience of the world are human inventions and conventions, including among these measures the concepts that we use to organize experience, as well as the quantitative metrics that we use to measure specific features of experience.
We have, for example, a concept of the volume of a closed space. There is no universal definition of “volume” or of “closed space,” but if a group of people all agree on what “volume” and “closed space” mean in a particular instance, then we can measure the volume of that space. There is no universal metric for this volume either, but if the same group of people agree on one— say, inches, or feet, or yards, or meters—then the volume becomes the same for everyone in that group. They all come up with the same number. In the process, by way of shared metrics, the subjective becomes objective, in the sense of becoming intersubjective. This example scales up to the most complex scientific measurements, for example, measuring the size and age of the universe. If you accept the definitions of relevant terms used by astronomers and astrophysicists, and if you accept the truth of the concepts they employ in their reasoning about the universe, then given the same data and the same instruments, the calculated age of the universe will be the same for everyone.
Against this conventionalist view of metrics, Plato and Aristotle were essentialists, holding that there were natural metrics that could be applied to nature and to reality. Plato, for example, has Socrates say that all things “must
be supposed to have their own proper and permanent essence, they are not in relation to us, or influenced by us, fluctuating according to our fancy, but they are independent, and maintain to their own essence the relation prescribed by nature.”23 The task of the philosopher is to discover what those essences are, in order to “carve” reality “at its [uniquely correct] joints” and not just any which way that humans please, “like a clumsy butcher,” that is, like the sophists.24
If, however, Protagoras and the Giants are right that humans are the measure of all things, then there are no natural joints at which to carve nature and thus no one correct carving. The measures, conceptual and quantitative, that we collectively choose to apply to nature derive from, but are not uniquely deducible from, experience. Experience often changes unpredictably, provoking new measures and ever-newer “carvings.” As an exemplary Giant, Protagoras does indeed “pull down from the heavens” what we mean by knowledge, truth, reality, and rationality. Knowledge becomes a species of opinions or beliefs about experience, which can be better or worse on pragmatic grounds, but not true or false in any absolute sense.
Borrowing ideas from the Pythagorean school of philosophers and from Heraclitus, Protagoras and Gorgias maintained that reality was not fully rational because every thing, in itself and in its interactions with other things, was composed of an ever-changing combination of opposing “forces” obeying their own laws of change (logoi). Nothing had an unchanging essence; there was only becoming and there was no changeless Parmenidean Being at all. For all allies of the Giants reason has a limited capacity for grasping a reality beyond experience. Antiphon argued that language was incapable of grasping the reality that existed external to the mind, and as reasoning is dependent on language, reasoning cannot grasp reality either. For Protagoras and Gorgias, poetry offered an aesthetic alternative to reason. It had the power to allow us to apprehend, non-discursively and non-rationally, something of the flux of the contending forces within all things, including within human beings. Through poetry, the mind felt something of the ultimate irrationality of reality and the ultimately tragic character of human existence.25 Plato, by contrast, was distrustful of poetry and in the Phaedrus had Socrates say that there was a place beyond poetry that was accessible to pure reason, uncorrupted by the senses, and this alone made knowledge in the strong sense possible.26 (These ideas of Antiphon, Protagoras, and Gorgias about language, reason, and the aesthetic will re-emerge in the eighteenth and nineteenth centuries.)
The battle lines between Gods and Giants have always been very clearly drawn. One or the other can be right, but not both. Knowledge claims can either be about a reality that is independent of our experience and our reasoning about it, or they are about our experience and reflect the ways in which we
reason about it. Either knowledge claims transcend context and are essentially true, validated by their correspondence with an external-to-mind state of affairs, or they are contextual, a function of applying pragmatically validated reasoning to experience. To claim that knowledge is about reality puts you in the camp of the Gods and commits you to the strong sense of knowledge, with coordinate conceptions of truth and rationality. To claim that knowledge is about experience puts you in the camp of the Giants and commits you to very different conceptions of truth and rationality.
What it boils down to is this: Is there a unique truth that the mind can know of any matter pertaining to what is external to the mind, and if so, how does the mind know it? With respect to the study of nature—understood as that which is external to and independent of human experience and its cause—the creators of modern science claimed that there was a uniquely correct account of what nature was really like and of how it caused our subjective experience of it. At the same time, however, they claimed that they produced such accounts by virtue of a distinctive form of experience-based reasoning that they practiced, the “scientific method” as it later came to be called. The new, “modern” science of nature claimed to have reality as its object, taking the side of the Gods, but the reasoning by which knowledge of nature was produced was anchored in experience, taking the side of the Giants. How can induction from particular experiences produce uniquely correct knowledge of what is independent of experience?
The founders of modern science were acutely aware of the force of these questions. They claimed to have penetrated experience to discover its unexperienced causes by reasoning about that very experience. This should seem paradoxical to us, and it was paradoxical to them, yet the paradox, unresolved, remains integral to modern science. The rhetoric of science continues to reflect a strong realist commitment that science tells us the truth about what is real, yet it does that empirically, hence inductively, conducting experience-based experiments and reasoning about their results. Two recent examples of this realism of science are the “discovery” of the Higgs boson and of gravitational waves using extremely complex instruments: the Large Hadron Collider (LHC) and the Laser Interferometry Gravitational Observatory (LIGO), respectively. Already in the seventeenth century, new realities—that the Earth moved, that air has weight and exerts pressure, that there was a world of “animals” not visible to the unaided eye—were realist claims based on what newly invented instruments were said to have revealed. Then and now there was no way of confirming these claims using our senses. We have to take the scientists’ word for it that their instruments were working correctly, that the outputs were not created by the instruments themselves,
