In 195-, living specimens of Paranthropus erectus were discovered in New Guinea. Their almost-human qualities recommended them to Australian industrialists, who announced plans for using them as factory slaves. This aroused Douglas Templemore, a British journalist, who had accompanied the scientific expedition that discovered the Paranthropus. He conceived a dramatic way of determining which these creatures were — apes or men — in order to decide what action should be taken, if any, to thwart the plans being made for them in Australia. Was the civilized world going to allow the “tropis,” as members of the species were affectionately called by the scientists who discovered them, to be unjustly exploited, their rights violated, their dignity transgressed? Or should it acquiesce in their being used, like horses and oxen, as beasts of burden in the service of man?
To get a legal decision on these matters by putting the status of the species to the test, Templemore arranged to have a captured female Paranthropus erectus impregnated, by artificial insemination, with his own sperm. He took care of the pregnant tropi, whose name was Derry; and when she gave birth to a male offspring, he brought the mother and “child” back to London, along with thirty other members of the species, for scientific study. While the mother was housed in the Zoo with the other tropis, Templemore kept the little one in his home. To carry out the plan which he had initiated with the artificial insemination of Derry, Templemore, not without anguish, killed his and her offspring with a shot of strychnine chlorhydrate and called in a physician to certify the death. Informed of the circumstances of the case, the perplexed Dr. Figgins notified the local constabulary. When the inspector arrived on the scene, the following conversation took place between him and Douglas Templemore.
“You are the father, I gather?”
“Your wife’s upstairs?”
“Yes, I can call her if you like.”
“Oh no,” the inspector hastened to assure him. “I wouldn’t ask her to get up in her condition! I’ll go and see her presently.”
“I’m afraid you are under a misapprehension,” said Douglas. “The child is not hers.”
“Oh … oh … well … is the — er — the mother here, then?”
“No,” said Douglas.
“Ah … where is she?”
“She was taken back to the Zoo yesterday.”
“The Zoo? Does she work there?”
“No. She lives there.”
“I beg your pardon?”
“The mother is not a woman, properly speaking. She is a female of the species Paranthropus erectus.”
With this revelation, Dr. Figgins then examined the dead infant more closely and declared it to be a monkey, not a boy. In response, Douglas Templemore produced an affidavit testifying to the infant’s peculiar origin. Written on the stationery of the Australian College of Surgeons, it read as follows:
- I hereby certify that this day at 4:30 A.M. I have delivered a pithecoid female, known as Derry, of the species Paranthropus erectus, of a male child in sound physical condition; and that the said birth took place as a result of an artificial insemination carried out by me in Sydney on December 9, 19- for the purpose of scientific investigation, the donor being Douglas M. Templemore. Selby D. Williams, M.D., K.B.E.
The police inspector was flabbergasted.
“Mr. Templemore,” he said, “what exactly do you expect us to do?”
“Your job, Inspector.”
“But what job, sir? This little creature is a monkey, that’s plain. Why the dickens do you want to . . .”
“That’s my business, Inspector.”
“Well, ours is certainly not to meddle . . .”
“I have killed my child, Inspector.”
“I’ve grasped that. But this . . . this creature isn’t a . . . it doesn’t present . . .”
“He’s been christened, Inspector, and his birth duly entered at the registry office under the name of Garry Ralph Templemore.”
“Under what name was the mother entered?”
“Under her own, Inspector: ‘Native woman from New Guinea, known as Derry.'”
“False declaration!” cried the inspector triumphantly. “The whole registration is invalid.”
“The mother isn’t a woman.”
“That remains to be proved.”
“Why, you yourself — ”
“Opinions are divided.”
“Divided? Divided about what? Whose opinions?”
“Those of the leading anthropologists, about the species the Paranthropus belongs to. It’s an intermediate species: man or ape? It may well be that Derry is a woman after all. It’s up to you to prove the contrary if you can. In the meantime her child is my son, before God and the law.” The foregoing conversations, as well as the circumstances under which they occur, are taken from the opening scene of a novel by Vercors entitled You Shall Know Them.
The main narrative focuses on a series of trials to determine whether Douglas Templemore is guilty of murder — infanticide, to be specific. The case finally goes up to the High Court of Parliament for adjudication, and before that august tribunal an impressive array of scientists, philosophers, and theologians present expert testimony bearing on the criteria for determining whether the Paranthropus erectus is or is not human. Listening to the debate of the experts on the pros and cons of each criterion, the Law Lords are greatly bemused by the question of fact whether Derry, the female tropi, is a woman; but they remain quite clear on the legal question involved: whether, if as matter of fact Derry must be considered a woman, Mr. Douglas Templemore should be legally — and morally — condemned as a murderer, to be convicted of one or another degree of homicide.
Those who have read the novel will know how Vercors solves both problems. I do not propose to give his secret away to those who have not read it.  My purpose in citing it is not to endorse the conclusions the novel reaches, but rather to call attention to the questions that perplex its leading characters. They are the very questions that will occupy us in the pages to follow. I would not be writing this book if I did not regard them as among the most serious questions with which we can be concerned. I have been in search of the right answers to them over many years, as a teacher of psychology and of philosophy, and as a student of the biological sciences, especially of the facts and theories of evolution in their bearing on man. My efforts to resolve the question of how man differs from other animals have, in recent years, been seriously complicated by technological achievements with computers that have persuaded many to call them “thinking machines,” and by the promises of future wizardry that will produce mechanical artifacts — robots — capable of simulating any human performance.
If I could be sure that all readers of this book had intellectual experiences similar to those that I have had in trying to make up my mind just where man stands in the scheme of things and how, in consequence, he should be treated; or if I could be sure that they, for reasons of their own, shared my estimate of the theoretical and practical importance of the questions raised in Vercor’s novel and dealt with in this book, I might dispense with these preliminaries and launch at once into an analysis of the problem itself, an examination and interpretation of the relevant scientific evidence, an assessment of conflicting philosophical arguments, and finally a consideration of the difference it makes whether we settle on one or another solution of the problem. In the absence of such assurances, I will spend a moment more trying to develop a concern comparable to my own about the difference of man and the difference it makes. Vague feelings about these matters are, I believe, at work in most members of the human race, and need only be brought into focus in order to be transformed from feelings into thoughts.
Imagine yourself on the tribunal trying the case of Douglas Templemore, I would say to such readers. What signs would you look for to determine whether the tropis were human or not? What sort of observable behavior on the part of the tropis would prove decisive in your mind, one way or the other? And if, by these signs or evidences, you knew them to be on this or that side of the line that divides men from other animals, would you take action accordingly not only in the case of Douglas Templemore, but also with respect to the Australian industrialists? Would your finding that the tropis are on the human side of the line be the sole, the indispensable, and the sufficient reason for convicting Templemore of murder and for crusading against the industrial exploitation of the tropis as chattel slaves?
If this is the way you would think about the matter, does it lead you to say that the killing of non-human animals cannot be called murder; or that, while it is possible for men to mistreat them in a fashion that is inhumane and morally reprehensible, no injustice is done to them simply by owning them as one owns tools or by using them as beasts of burden or as implements of work? Would you go so far as to say that non-human animals have no rights that must be respected, or at least no rights that, if respected, would secure them from being owned and used as chattels? And if you would say this, what would have to be the character of the difference between men and other animals to justify your policy of treating men and other animals so differently, assuming for the moment that you thought your policy needed justification?
Suppose that you were convinced that men and other animals differed only in degree, or that such differences in kind as might appear to put a chasm between them could be shown to arise from underlying or bedrock differences in degree? Would that type of difference — a difference merely of more and less of the very same traits or capabilities possessed to some degree by all animals, human and non-human — supply the ground for exonerating Douglas Templemore as a murderer and the Australian industrialists as enslavers, if it were ascertained, as a matter of fact, that the tropis, while possessing the same traits and capabilities that we find in human beings, possessed them to a degree distinctly less than the least competent man?
Give an affirmative answer to this question, and you would then be confronted by a whole series of other questions that might perplex you. Men differ from one another in degree, sometimes quite remarkably if one considers the extremes of superior endowment at one end of the scale and of subnormal deficiency at the other. If a difference in degree suffices to justify a difference in treatment, why would not superior men be justified in treating inferior men in whatever way men think they are justified in treating non-human animals because the latter are inferior in degree?
Rightly or wrongly, the ancient Greeks conceived themselves as vastly superior to the barbarians; the African slave traders and the American slaveowners of the seventeenth and eighteenth centuries regarded the Negroes as barely human; in this century, the Nazis looked upon Jews and Slavs as racial inferiors. In each case, the inferior human beings were treated as a despised or hated animal is treated by men. If you think that the Greeks, the Negro enslavers, and the Nazis were wrong; if you think that their policies were morally reprehensible violations of the dignity of man, do you charge them with being wrong as a matter of fact (because barbarians are not inferior to Greeks, Negroes to white men, or Jews and Slavs to Germans), or do you maintain instead that if the facts were as they claimed them to be, they would still be morally wrong (because a difference in degree, no matter how large the gap between superior and inferior individuals, groups, races, or for that matter, species, does not justify a difference in treatment)?
If you give the latter answer and do not limit it to differences in degree within the species that biologists classify as Homo sapiens, do you have any way of separating yourself from the philosophical vegetarian who regards the eating of animal flesh with the same moral repugnance that most men now regard cannibalism? Carry that point of view to its logical conclusion, and ask yourself whether the men who hunt inferior forms of animal life are murderers when they kill, or enslavers when they capture and cage, their prey. Eliminate the instances in which the killing is in self-defense because the animal attacks, or, as in the case of certain insects or vermin, it is disease-bearing and so is a threat to human health. Think instead of killing animals for the enjoyment of the sport; or, in another context, of killing them for the purposes of vivisection in the course of medical research. Now, if these actions can be justified by nothing more than a difference in degree between human and non-human animals, why is not the same justification available for the actions of Nazis or other racists?
It will not do merely to point out that, as a matter of fact, Jews are not racially inferior to Nordics, or Negroes to white men; for it is also a matter of fact that substantial differences in degree separate the upper from the lower limits in the scale of human endowment. At some future time when overpopulation threatens the survival of the human race, suppose that the truly superior men, regardless of race or nationality, band together to exterminate their inferiors and have the means of doing so at their disposal. Would this, in your eyes, be a morally acceptable solution of the problem of overpopulation?
If these questions bother you, perhaps you would like to return to the point of their origin and see what happens when you embrace the opposite point of view; namely, that only a difference in kind between human and non-human animals can justify the difference between the kind of treatment that we accord men and the kind of treatment that we accord other animals. Adopting this point of view, you can invoke the moral, juridical, and theological distinction between persons and things (which rests on a difference in kind, not a difference in degree); you can attribute to men and men alone the dignity that attaches to persons, not things, as well as the rights that inhere in persons, not things; you can explain why things, even though they can be misused in various ways and even destroyed, can never be murdered, slandered, enslaved, lied to, stolen from, or otherwise injured — for only persons can suffer injustice.
In spite of the undeniable facts of individual differences in degree, which often place a wide gulf between one human being and another, you can hold onto the truth that is contained in the statement that all men are born equal because, being born human, they have the equality of persons, an equality or sameness in kind that overrides their various inequalities in human endowment or accomplishment. And understanding this truth that way will carry you to its corollary — that the inequality, or difference in kind, between things and persons exempts us from treating things as we are required to treat persons.
You and I know, of course, that the history of mankind right down to the present century is replete with the most grievous violations of the dignity of man. We may even suspect, taking human history as a whole, that the violations — the injustices perpetrated on men by men — have been the rule rather than the exception. But we also know that, since the beginning of civilized life on earth, the small voice of conscience has also been heard denouncing these atrocities; and that with the passage of time and, especially in recent centuries, it has spoken out with increasing vigor, gained the attention of more and more men, and inspired crusading reforms for human rights and against human injustices.
Will it eventually prevail, establish the just treatment of persons as the rule in human affairs, and make mass criminality as much the exception as individual criminality is the exception within the confines of most civilized societies? We may not be able to answer that question, which calls for a prediction difficult to make, but each of us, it would seem, should be able to answer another question, one that calls only for an expression of preference on our part. Do we want justice to prevail in human affairs? Or would we be equally pleased to have the voice of conscience gagged, and to have men in the mass persist in their treatment of other men as if they were not different in kind from — and no better than — non-human animals?
That question, unfortunately, throws you right back to the very center of the problem with which you started to grapple when you assumed a seat on the tribunal trying the case of Douglas Templemore. You have explored it in various directions and in widening circles, but you cannot get away from a central question of fact — the question of how man differs from other animals. Basically in kind or basically in degree? Inseparable from that question is the question about the practical consequences that follow — the question about the difference it makes whether the difference between men and other animals is one of kind or of degree.
Both questions, on closer examination, involve complications that I have either not touched on or barely indicated. In ways that I cannot explain until the latter part of this book, the question of fact is complicated by the simulation of distinctively human performances by computer-like machines — machines that, at some time in the not so distant future, may assume the guise of persons by virtue of their performances and may, in consequence, command the respect and treatment that we accord only to persons. The question of practical consequences, whether with respect to men and other animals or with respect to men and machines, is itself further complicated by a number of considerations that I have not mentioned or made clear, again because to do so effectively is possible only at the end of this book, not at its beginning.
The reader will appreciate, I hope, that in these opening pages I have sought, mainly by questions, to solicit his agreement with my own sense of the importance of the problems with which this book deals. If he thinks he can detect, here and there, in the way the questions have been asked, that I have assumed answers to certain questions in order to ask others, he may be right; but I can promise him that if certain answers have been assumed, the assumptions will not go unchallenged. They will be subject to critical scrutiny later, at points where it is more appropriate or feasible to do so.
The question about man has been asked in a variety of ways. We are all familiar with the ways in which philosophers and theologians have traditionally posed it: What is man? How shall man’s nature be defined? What is the essence of humanity? And, recently, existentialist thinkers have appeared to strike out in another direction by asking, Who is man? In all these forms the question tends to bypass or ignore the contributions of the biological and behavioral sciences to the study of man. No scientist who understood his business would attempt to answer questions couched in such terms, though he would, quite rightly, suspect that much knowledge in his possession and still more within his competence to acquire would have critical relevance to any answer that might be given to questions thus formulated. As thus formulated, the question about man has a philosophical or theological cast that tends to protect it from the intrusion of scientific evidence and tends to elicit only the kind of answers that theologians have given in the course of explicating the dogmas of religious faith, or that philosophers have discovered by intuition, propounded by reason, or framed within the systematic context of an over-all view of the world.
That is why it seems to me preferable to pose the question in another way and ask how man differs from everything else on earth — from inert bodies, from other living things, especially the higher forms of animal life, and from machines, especially such mechanical contrivances as computers or robots invented to simulate human intelligence in operation. Asked in this way, the question calls for a multitude of comparisons — comparisons of the sort that biological and behavioral scientists have carefully and patiently made. Asked in this way, the question becomes impossible to answer without consulting all the available scientific evidence, the relevance of which cannot be doubted or discounted by evasive tactics on the part of philosophers or theologians. For all that, the question thus formulated, is, as we shall see, not a purely scientific question.
Philosophical analysis plays an indispensable part in clarifying the question by indicating the range of the possible answers and also by determining the criteria for interpreting the relevance of particular items of evidence. In addition, it helps us to evaluate the probative force of the scientific data — to see, with regard to this or that piece of evidence, which of the possible answers it tends to support and the extent to which it approximates being decisive in the resolution of the problem.
At the same time, the comparative question about how man differs from everything else on earth underlies the traditional philosophical and theological forms of the question about man that, on the surface at least, appear to be non-comparative. To know man’s quiddity, to define human nature or to understand its essence, and even to speculate about man’s identity — who he is — presupposes that one knows and understands how man differs from everything else. This presupposition, unfortunately, was often overlooked when the question was traditionally asked by philosophers in its non-comparative form. They often appeared to proceed as if they could, by contemplating or by examining man in isolation from everything else, reach a definitive answer about his nature, essence, or identity.
Nevertheless, whether they were aware of it or not, the answers they did give always contained one or another of the possible answers to the question about how man differs, bearing out the point that the latter question is the inescapable underlying one in any approach to the consideration of man.
In The Conditions of Philosophy,  I tried to show that there are some purely philosophical questions, just as there are some purely scientific questions — the former being questions that philosophers alone are competent to answer, just as the latter are questions that scientists alone are competent to answer, the answers in both cases having the same character as knowledge (i.e., reasonable and criticizable opinion, testable and falsifiable by experience). The comparative question about man is neither a purely philosophical nor a purely scientific question. It is instead what I have called a mixed question, a question that cannot be adequately answered either by scientists alone or by philosophers alone, but only by their collaboration — by combining the findings of scientific investigation with the contributions of philosophical analysis and criticism.
To say that philosophy and science are knowledge in the same sense is to say that both are empirical knowledge: their theories or conclusions are falsifiable by experience. They have the status of testable and corrigible opinions, capable of some relative degree of truth, but never attaining certitude or finality. But while both are empirical by virtue of submitting their theories or conclusions to the test of experience, the experience that philosophy appeals to is the common experience of mankind, experience that is possessed without any effort of investigation, whereas the experience that science appeals to is special experience, experience that can be obtained only by deliberate and methodical investigation. Science, in other words, is investigative knowledge about that which is or happens in the world; philosophy, insofar as it is knowledge of that which is or happens, is non-investigative, precisely because it relies on and appeals to the experience that all men enjoy and share without any effort of investigation on their part. 
By virtue of the fact that philosophy, employing com-mon experience, has a method of its own, it also has certain questions of its own — questions that it and it alone is competent to answer, questions that cannot be answered by scientific and historical research because they are questions on which investigation, no matter how ingenious or extensive, is unable to throw light. Similarly, there are questions that can be answered solely by investigation and in the light of the data of special experience that results from investigation. These are purely scientific or historical questions, to the solution of which philosophy can make no direct contribution. But there are certain questions which, while subject to investigative efforts, cannot be adequately solved by investigation alone. These are the questions that I have called “mixed” to indicate that the solution of them depends upon some combination of philosophical know-ledge with other forms of empirical knowledge obtained by investigation, whether by scientific inquiry or by historical research. 
Though this book will, in my judgment, amply demonstrate that the question about man is a mixed question, it has not always been recognized to be one. On the contrary, it has been treated for almost twenty-five centuries of Western thought as if it were a purely philosophical question. This is partly because the question was traditionally posed in a non-comparative form, and partly because until recently little scientific evidence was available for answering the comparative question about how man differs. Most of the philosophers who proposed answers did so entirely in terms of philosophical theories, hypotheses, or conclusions based on common experience alone.
A few philosophers showed some awareness of scientific evidence — evidence obtained by investigation — that had some bearing on the question, but at the time this evidence was either so slight or so indecisive that even they treated the question as if it were a purely philosophical one. It is only in the last hundred years, at the most, that the mixed character of this question has forced itself upon our attention; and it is only in the last hundred years, or even less, that the mounting masses of scientific evidence from a wide variety of research pursuits have come to play a critical role in the consideration. of how man differs from everything else on earth. Yet even now there are philosophers who persist in ignoring the scientific evidence, just as there are scientists who fail to recognize its philosophical dimensions and proceed as if their data could solve it without the help of philosophical analysis.
A philosophical clarification of the mixed question about man will, I hope, be achieved in Chapter 2, where I will try to set forth, exhaustively, the range of possible answers to a more general question; namely, how any object that we can consider differs from any other. The various possible ways in which any two comparable things can be said to differ exhaust the ways in which man can be said to differ from everything else on earth.
Everyone is familiar with the usual alternative answers that we give when we are asked how two things differ: either we say that they differ in degree or we say that they differ in kind. But though the words “degree” and “kind” are frequent and familiar in everyday speech, they are seldom understood by the persons who use them in ordinary discourse; nor, as we shall see, is the distinction between these two modes of difference adequately grasped by the scientists who use these words. In addition, the alternatives thus far mentioned — difference in degree and difference in kind — by no means exhaust the possible modes of difference. A difference in kind may be only apparent, as compared with one that is real. Since an apparent difference in kind reduces to a difference in degree, we need only consider differences in kind that are real; among these, some are superficial, and some radical. Hence there are three basically distinct modes of differences:
- 1. difference in degree,
- 2. superficial difference in kind, and
- 3. radical difference in kind.
These distinctions will, I hope, become clear in the following chapter, both as they apply to any two com-parable things and also as they apply to the comparison of man with anything else. Here I wish only to point out that unless these distinctions are made and understood, the various answers that the philosophers have given to the question about man cannot be seen as constituting the opposed positions in a three-sided controversy; nor, without this philosophical clarification of the modes of difference, can the scientific literature bearing on the question be read critically.
With this philosophical analysis set forth in Chapter 2, clarifying the question of man’s difference by reference to a framework of possible answers, I will, in Chapter 3, consider the different types of evidence that bear on the question and the conditions under which a decisive resolution of it may be reached, or at least something closely approximating a decision in favor of one as against the other two modes of difference. And since Chapter 3 will conclude the introductory part of this book, I will try there to prepare the reader for the series of chapters that constitute Part Two, by outlining the course of the argument that lies ahead — the sequence of steps that will bring us to the appraisal we can make at this time of the state of the mixed question about man. Then, in Part Three, we will be concerned with the theoretical and practical differences it makes how the question about the difference of man is answered.
When the conflicting answers to a question do not make a significant difference to us — either a difference to the way we think about things and to what we believe or a difference to the way in which we act and to the practical policies we adopt the question is academic in the worst sense of that term. William James and the pragmatists were quite right to dismiss such questions as trivial and to call upon philosophers and men generally to concentrate on what James called “vital options” — questions to which the conflicting answers make a significant difference.
The question about man, with which this book is concerned, is far from being an academic or trivial question; it is a vital option in James’s sense of that term. How we answer it makes a great difference to us — both to the principles and policies governing our actions and to many of our fundamental beliefs and disbeliefs. We tend to be impatient with extended analyses, elaborate arguments, and thoroughgoing examinations of evidence, unless we can foresee that the effort will be repaid in the form of important practical or theoretical consequences. A brief preview of the consequences to be discussed in Part Three may persuade the reader to be patient with all the steps of thinking through which he must go in order to have a clear and solid foundation for assessing the difference it makes how man differs from other things.
We will find, on the one hand, that it makes a great practical difference whether we say that man differs only in degree from other things or that he differs in kind as well. And, on the other hand, we will find that regarding all of man’s differences in kind as only superficial or regarding at least some of them as radical has serious theoretical consequences — for science, for philosophy, and for religion.
The practical consequences of regarding man as differing only in degree from other animals all turn on the abrogation of the distinction we make between persons and things — a distinction that involves a difference in kind. The dignity of man is the dignity of the human being as a person — a dignity that is not possessed by things. Precisely because we do not attribute to them the dignity of persons, we feel justified in treating things — other animals or machines — as means, as instruments to be used or exploited. The dignity of man as a person underlies the moral imperative that enjoins us never to use other human beings merely as means, but always to respect them as ends to be served.
The condemnation of slavery and other forms of human exploitation as unjust is an immediate corollary of this basic normative principle. Hence, it would appear to make a great practical difference whether we can preserve the distinction between men as persons and all else as things, or must abrogate it because men differ from all else only in degree.
What are the opposite theoretical consequences of asserting a superficial or a radical difference in kind between man and other things? We will find, on the one hand, that the view that man differs radically in kind harmonizes with certain fundamental beliefs in all orthodox forms of Judaism and Christianity: for example, the belief that man and man alone is, as a person, made in the image of God; the belief that man and man alone is a special creation of God; the belief that man and man alone has an immortal soul or is destined for personal immortality; the belief that man alone has free will and carries the burden of moral responsibility.
But this view of man does not harmonize with the fundamental principle of continuity in nature, to which almost all natural scientists subscribe. More specifically, it challenges the principle of developmental or phylogenetic continuity, which is central to the theory of evolution and which evolutionists think is as applicable to man as it is to other living organisms. In addition, the view that man differs radically in kind, entailing as it does the conception of man as having a non-physical factor in his make-up, is embarrassing, to say the least, to the new theology that rejects the traditional tenets of orthodox Christianity.
We will find, on the other hand, that the view that man differs in kind, but only superficially, harmonizes with the principle of continuity in nature. It also harmonizes with the main tenets of materialism and naturalism in philosophy, and gives support to the fundamental disbeliefs of the prevalent secularism. By the same token, it challenges and tends to repudiate the traditional dogmas of orthodox Judaism and Christianity. The philosophers who have held this view have been, for the most part, anti-religious. Far from concealing their antagonism to religion, they have outspokenly espoused the adverse effects of their views of nature and of man upon traditional religious beliefs. In addition, this view, entailing as it does the denial of anything non-physical in the nature of man, raises serious if not insuperable difficulties for the metaphysical theory of the will’s freedom, as well as for the philosophical doctrine that freedom of choice is the sine qua non of moral responsibility.
This must suffice as a sketchy preview of the consequences for action and for thought of the answers we give to the question about man. These matters will be more thoroughly treated in Chapters 17 and 18. We shall then have explored all angles of the question about the difference of man and be in a position to examine with thoroughness the difference it makes.
1. From You Shall Know Them by Vercors, copyright 1953 by Jean Bruller, with permission of Little, Brown and Co. A paper-back reprint of it has just been published. I heartily recommend Vercors’ novel not only for the pleasure of a well-told story, but also for a learned exploration of the criteria involved in differentiating between humans and other animals.
4. See ibid., Chapter 2, pp. 38-42; Chapters 6-7; and Chapter 12, esp. p. 216-217. Let me stress the two related aspects of every mixed question. On the one hand, philosophy, as we have seen, is indispensable in the clarification of the question and in laying down the criteria for interpreting and judging the relevance and force of the evidence obtained by investigation. On the other hand, since the mixed question is not beyond the scope of investigation, it can never be adequately answered on the basis of common experience alone. Purely philosophical answers to mixed questions are corrigible by science, just as common sense is corrigible when the latter forms opinions about matters on the basis of common experience alone, in spite of the fact that special experience is obtainable and should be sought.
Not all mixed questions are of the same type. Some arise from an apparent conflict between science and common-sense opinion. These serve to test the truth of competing philosophical theories by challenging them to resolve the conflict without giving up either the truth of common-sense opinion or the truth of science. I dealt in The Conditions of Philosophy with a striking example of this type of mixed question, involving a conflict between the common-sense beliefs in the reality of the individual physical objects of common experience and the assertion, by some scientists, of the reality of elementary particles. The mixed question about man is of a different sort. Here the solution of the problem of how man differs requires us to consult all the relevant scientific data and theories and to bring to bear on them the applicable philosophical analysis and arguments. It requires us, in addition, to have recourse to philosophical thought in order to get the question itself properly framed and understood and in order to lay down criteria for interpreting and judging scientific evidence and philosophical arguments in their relation to each other. But what is most extraordinary about the mixed question concerning man, as will become apparent in the concluding chapters of Part Two, is that we can envisage in the future the possibility of scientific efforts that will have effect either of falsifying a traditional philosophical theory or of confirming its relative truth.