On Purpose

On Purpose

by Michael Ruse


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An accessible history of the idea of purpose in Western thought, from ancient Greece to the present

Can we live without the idea of purpose? Should we even try to? Kant thought we were stuck with it, and even Darwin, who profoundly shook the idea, was unable to kill it. Indeed, purpose seems to be making a comeback today, as both religious advocates of intelligent design and some prominent secular philosophers argue that any explanation of life without the idea of purpose is missing something essential. On Purpose explores the history of purpose in philosophical, religious, scientific, and historical thought, from ancient Greece to the present. Accessibly written and filled with literary and other examples, the book traces how Platonic, Aristotelian, and Kantian ideas of purpose continue to shape Western thought. Along the way, it also takes up tough questions about the purpose of life—and whether it’s possible to have meaning without purpose.

Product Details

ISBN-13: 9780691195957
Publisher: Princeton University Press
Publication date: 11/26/2019
Edition description: Reprint
Pages: 320
Sales rank: 780,840
Product dimensions: 5.00(w) x 8.10(h) x 1.00(d)

About the Author

Michael Ruse is the Lucyle T. Werkmeister Professor of Philosophy and Director of the Program in the History and Philosophy of Science at Florida State University. His many books include Darwinism as Religion, The Philosophy of Human Evolution, and The Darwinian Revolution.

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ARISTOTLE (384–322 BC) SAID, "Knowledge is the object of our inquiry, and men do not think they know a thing till they have grasped the 'why' of it (which is to grasp its primary cause)." He was not the first to raise the question of causation, for it was nigh an obsession of his philosophical predecessors, back through his teacher Plato (ca. 429–347 BC) to Socrates (469–399 BC), and to the earlier "pre-Socratic" thinkers, including Empedocles (ca. 495–435 BC), Anaxagoras (ca. 510–ca. 428 BC), and the atomist Democritus (ca. 460–ca. 370 BC). They all grasped that in some sense causation — what it is that makes things happen — is (or is often taken to be) both a backward-looking matter and a forward-looking matter. The nail is driven into the piece of wood. Backward-looking in the sense that this happens because a hammer was picked up and used to hit the head of the nail; forward-looking in the sense that this happens because the builder wants to tie the planks together to support a roof. The builder did this "on purpose" or "for a purpose." He wanted that end. A roof was something of value to him.

I shall argue that this forward-looking side to causation — the subject of our inquiry — lends itself to three different approaches. I do not pretend to originality in spotting these approaches. Others, for instance, R. J. (Jim) Hankinson and Thomas Nagel, have certainly remarked on this triune side. It is in tracing the way that it persists that makes the story so interesting and illuminating. The first approach, often known as "external" teleology, is the most obvious and intuitively plausible. It involves a mind, whether human or divine or something else. "For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life" (John 3:16). God, right now, let Jesus die on the cross, so that you, the sinner, should have everlasting life in the future. The second approach, often known as "internal teleology," is a bit trickier. It involves a kind of life force in some sense, something that need not be conscious, and actually in the broader sense need not even be alive. It might be more a kind of principle of ordering about the world, something that makes everything essentially end-directed. When we see it being argued for, we shall get a better sense of what it is all about. These two notions of purpose, of teleology, go back readily to the Greeks. The third kind of approach we might call "eliminative" or, more positively, "heuristic" teleology, seeing forward-looking causation — purpose — as in some sense purely conceptual, something we might use to understand the world but in no sense constitutive of the world. This label would apply to — or at least is anticipated in — the approach of Democritus and comes out more vividly in the (several centuries later) poetry of the Roman Lucretius (ca. 99–ca. 55 BC). But it is not until the modern era that this approach could be developed fully.

With respect to the first two approaches, it is not always easy to tell if one has either external or internal teleology. In Emily Dickinson's poem, is there a designer god behind everything or is it all a matter of an impersonal force, an Immanent Will (as it has sometimes been called)? What we can say is that Plato offered the first full discussion of external teleology and Aristotle the first full discussion of internal teleology, with the atomists at the least the forerunners of the heuristic option.


There are two main sources for Plato's thinking about purpose, about teleology. The first is in the Phaedo, the dialogue about Socrates's last day on Earth. It is a middle dialogue, and given the nature of the discussion is generally considered a vehicle for Plato's own thinking — apart from anything else, Plato notes explicitly that he himself was not present, which gives us a clue that there has to be some element of creativity — although there is a comparable discussion attributed to Socrates himself by Xenophon (ca. 430–354 BC), and a version of the argumentation may go back to Anaxagoras. Surrounded by the young men who are his followers, much of the discussion Socrates directs is (hardly surprisingly) about key issues, such as the nature of the soul — more on this shortly — and questions about existence beyond this life. Almost in passing, Socrates raises the question of the deity. It is not so much a question of offering a formal proof but in showing how we need such a concept in order to make sense of the ways in which we understand things.

Normally, such an issue doesn't arise. "I thought before that it was obvious to anybody that men grew through eating and drinking, for food adds flesh to flesh and bones to bones, and in the same way appropriate parts were added to all other parts of the body, so that the man grew from an earlier small bulk to a large bulk later, and so a small man became big." This is backward-looking causation, that is, what we have seen called "efficient causation." Plato acknowledges that this is not a bad explanation — we do get bigger thanks to eating and drinking — but it is in some sense incomplete. Why would one bother to eat and drink? Why would one want to grow and put on weight? See here how the notion of value is coming in. What is the point of doing something? What's the purpose? Why do we want the end result? Here we need to switch to forward-looking causation or (what within the Aristotelian system was called) "final cause." We are — or rather will be — better off if we grow. This is crucial. Something happens that we value. Which is just fine and dandy, but why should it happen? Why doesn't eating and drinking make us lose weight? "One day I heard someone reading, as he said, from a book of Anaxagoras, and saying that it is Mind that directs and is the cause of everything. I was delighted with this cause and it seemed to me to be good, in a way, that Mind should be the cause of all. I thought that if this were so, the directing Mind would direct everything and arrange each thing in the way that was best." So now one has a guide to discovery. "Then if one wished to know the cause of each thing, why it comes to be or perishes or exists, one had to find what the best way was for it to be, or to be acted upon, or to act."

Note that we have a heuristic here but more than this, although it is more a presupposition than an explicit proof. Things don't just happen. They are ordered for the best, and this is done by a mind — or rather by a Mind. The teleology in this sense is external — imposed upon the world from without.

Atomist Interlude

Pause for a moment, to dig a little more deeply. You have features, let us say teeth or hands or whatever. These are brought about through efficient causes, the physiological effects of eating and drinking. They also have purposes or ends, what we are going to call final causes. These features are of value. And God or a Mind is being invoked to explain everything. The Design Argument, although note that truly we have a two-part argument here. First, to the design-like nature of the world. Second, from this nature to a God. Plato more or less takes the first part of the argument as a given and is focused on the second part. Aristotle, as we shall see, as a sometime very serious biologist, has more focus on the first part. In order to bring out these two moves, let me make continued use of the fact that I am not now writing a straight history of philosophy but a history of ideas directed toward the present, and so I have greater freedom to move back and forth in time. Interrupt Plato and turn for a moment for contrast and illumination to the atomists. They argued that we have an infinite universe, infinite time, and nothing but particles — atoms — buzzing around in space or the void. Every now and then they will join up, and first we have disembodied parts — an eye here and a leg there. In the words of Lucretius, writing in the tradition of the materialist Epicurus (341–270 BC), who in his physics followed Democritus:

At that time the earth tried to create many monsters with weird appearance and anatomy —
Thus far, nothing works. It is just a mess, of no value whatsoever. But then, given infinite time, things joined up in functioning ways.

First, the fierce and savage lion species has been protected by its courage, foxes by cunning, deer by
This obviously is a direct challenge to the second move in the Design argument. The immediate objects of Lucretius's poem are probably the Stoics (see below), but Plato is in direct line. In the Sophist, having invoked a deity to explain the design-like nature of everything, animals, plants, the earth itself, he asks bluntly, "Are we going to say that nature produces them by some spontaneous cause that generates them without any thought, or by a cause that works by reason and divine knowledge derived from a god?" The first disjunct is the atomist's happy reply. No need to invoke a god or whatever to explain purpose — "intelligence, along with color, flavor, and innumerable other attributes, is among the properties that supervene on complex structures of atoms and the void." Which in turn rather implies that the atomists allow the first part of the argument. Things, organisms in particular, show purpose. They have features serving their ends (fierceness, cunning, running ability) or our ends (faithfulness, strength for work, wool coats, milk and meat). Lucretius admits this, but reluctantly. It is certainly not part of reality. Eyes were not made for seeing or legs for keeping us upright. It is rather that the eyes and legs appeared and then were put to use. To think otherwise is to get things backward.

All other explanations of this type which they offer are back to front, due to distorted reasoning.
Lucretius certainly accepted end-directed thinking when it comes to human artifacts.

Undoubtedly too the practice of resting the tired body is much more ancient than the spreading of soft beds;
It is just that he didn't want this analogy carried over to the living world. No values out there.

Quite different from these are all the things which were first actually engendered, and gave rise to the preconception of
Since he feels the need to warn us against it, Lucretius obviously recognizes that people think of organisms (or their parts) as having purposes. He is not prepared to deny that the world, the organic world in particular, shows design-like features. As an aside, therefore, treating the atomists in their own right and not just as a foil for Plato and Aristotle, perhaps rather than saying that atomists like Lucretius gave a heuristic understanding to purpose — something positive in the sense that it leads to insights, and that we shall see in later thinkers — it is more accurate to say that (outside human artifacts), they didn't really think it existed at all in reality (in the sense of having actual design or purpose) and only comes in as a sign of weakness in thinking. Either way, it is this approach that Plato (and almost certainly Socrates) thought improbable to the point of impossibility. No matter how infinite time and space may be, it isn't going to happen. To use a modern analogy, no number of monkeys randomly striking the keys of no number of typewriters is ever going to turn out the Collected Works of William Shakespeare, or to use a more contemporary example of the Roman orator and philosopher Cicero (106–43 BC), no number of letters of the alphabet shaken up in a bag are ever going to produce the Annals of Ennius, an epic poem about Roman history.

The World Soul

The context here is with living beings. As the discussion goes, Plato makes it clear that he is happy to extend forward-looking thinking to inanimate objects also; they too can be considered teleologically in terms of the designing intelligence deciding what is best for them. We can ask about purposes, as long as we can see value. Apparently, it would be perfectly proper to say that the earth is round rather than flat because it is in the middle of the universe, and that this is the best possible place for it to be. In other words, the earth is round in order that it might be in the middle of the universe. Unfortunately, in Plato's opinion, Anaxagoras, who has been noted as a forerunner in thinking about these sorts of things, gave up on the job and didn't really try to carry things through thoroughly. Having introduced the notion of end causes, he rather ignored them. In another dialogue, the Timaeus — very influential for this, or rather the first part, was virtually the only actual dialogue known to later generations until well into the Middle Ages — Plato himself took up the job and showed how it is that Mind orders everything for the best. Well known is the central claim of the Timaeus that the world — meaning the universe — is or was essentially disordered and then a designing mind, or Mind, imposed functioning order upon it. There is discussion about whether this Mind — what Plato called the Demiurge — was in fact a being who acted temporally, imposing its will upon an existing universe, one that had no beginning and will have no end. Or is it more a principle of ordering that always had its will impressed upon physical reality? Most of a philosophical vein have gone for the second interpretation, but there have been those (including Aristotle) opting for reading Plato as positing an actual creation. The Stoics (of whom more shortly) liked this idea for it tied in with their belief of eternal recurrence — worlds have beginnings and ends, and then start all over again. No real matter to us. Either way, the Demiurge is a designer from the already-existing rather than a Creator from nothing, as is the Christian God.

The Demiurge is external to the world, but it goes one step further than perhaps necessary, for it imbues the world with a soul of its own. By "world," as is made clear by a later work, is meant the universe — it is quite false "that all the bodies that move across the heavens were mere collections of stone and earth." By "soul" here (and elsewhere) Plato is not so much thinking of the Christian sort of soul, something purely mental and conscious — although that is certainly involved, especially intelligence — but also (as comes across clearly in The Republic, where Plato distinguishes but recognizes the appetitive part of the soul from the parts producing thinking and courage) something of the general life force that drives organisms forward. So, in other words, the universe is a living entity and ipso facto teleological thinking about its parts, both what we would normally judge the living and the nonliving, is not just appropriate but demanded: "the world is an intelligent being with its own soul, an arrangement ensuring that it is intelligently governed all the way down." And value is right at the center of this. In Candide, Voltaire, through the mouthpiece of the philosopher Dr. Pangloss — who manages to get the clap and consequent rotting of virtually all of his bodily parts — pokes fun at the claim of Gottfried Leibniz (1646–1716) that this is the best of all possible worlds. The great German came by his thinking honestly, because this is at the heart of Plato's value-impregnated vision of the world. "Well, if this world of ours is beautiful and its craftsman good, then clearly he looked at the eternal model." The reference here was to the Platonic Theory of Forms, most clearly discussed in The Republic. Deeply influenced by the School of Pythagoras, which combined a perhaps expected veneration of mathematics with a perhaps unexpected worship of the Sun, Plato argued that just as in this world we have physical objects (including organisms) that in some real sense owe their very being to the Sun, connecting all together through being the source of energy and also the power through which we can see the objects, so there is a world of rationality where we find ideal archetypes (Forms or Ideas) with the ultimate, the Form of the Good, analogously to the Sun connecting all together through giving the Forms their very being and enabling us through the intellect to know them.


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Table of Contents

Acknowledgments ix

Prologue xi

1 Athens 1

2 Jerusalem 23

3 Machines 42

4 Evolution 61

5 Charles Darwin 76

6 Darwinism 91

7 Plato Redivivus 114

8 Aristotle Redivivus 129

9 Human Evolution 153

10 Mind 166

11 Religion 195

12 The End 210

Epilogue 239

Notes 241

Bibliography 267

Index 285

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From the Publisher

"Do humans have purposes and values? Michael Ruse, after ‘a lifetime's quest for understanding,' concludes ‘yes.' In this book, he journeys from Plato and Aristotle, through St. Augustine and Kant, to Darwin. The exploration is scholarly and profound, as well as eminently readable. There is much to learn from On Purpose and much to relish while reading it."—Francisco J. Ayala, University of California, Irvine

"There are no other books on the story of purpose in Western thinking that have such a broad, comprehensive, and historical approach. Michael Ruse probably knows this subject better than anyone else. He is always clear-eyed, and his writing is unique—conversational, personal, and irreverent."—Richard Richards, University of Alabama

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