8. SCIENTIFIC KNOWLEDGE.--Still, the knowledge of the world which we have been discussing is rather indefinite, inaccurate, and unsystematic. It is a sufficient guide for common life, but its deficiencies may be made apparent. He who wishes to know matter and mind better cannot afford to neglect the sciences.

Now, it is important to observe that although, when the plain man grows scientific, great changes take place in his knowledge of things, yet his way of looking at the mind and the world remains in general much what it was before. To prevent this statement from being misunderstood, I must explain it at some length.

Let us suppose that the man in question takes up the study of botany.

Need he do anything very different from what is done more imperfectly by every intelligent man who interests himself in plants? There in the real material world before him are the same plants that he observed somewhat carelessly before. He must collect his information more systematically and must arrange it more critically, but his task is not so much to do something different as it is to do the same thing much better.

The same is evidently true of various other sciences, such as geology, zoology, physiology, sociology. Some men have much accurate information regarding rocks, animals, the functions of the bodily organs, the development of a given form of society, and other things of the sort, and other men have but little; and yet it is usually not difficult for the man who knows much to make the man who knows little understand, at least, what he is talking about. He is busying himself with _things_--the same things that interest the plain man, and of which the plain man knows something. He has collected information touching their properties, their changes, their relationships; but to him, as to his less scientific neighbor, they are the same things they always were,--things that he has known from the days of childhood.

Perhaps it will be admitted that this is true of such sciences as those above indicated, but doubted whether it is true of all the sciences, even of all the sciences which are directly concerned with _things_ of _some_ sort. For example, to the plain man the world of material things consists of things that can be seen and touched. Many of these seem to fill s.p.a.ce continuously. They may be divided, but the parts into which they may be divided are conceived as fragments of the things, and as of the same general nature as the wholes of which they are parts. Yet the chemist and the physicist tell us that these same extended things are not really continuous, as they seem to us to be, but consist of swarms of imperceptible atoms, in rapid motion, at considerable distances from one another in s.p.a.ce, and grouped in various ways.

What has now become of the world of realities to which the plain man pinned his faith? It has come to be looked upon as a world of appearances, of phenomena, of manifestations, under which the real things, themselves imperceptible, make their presence evident to our senses. Is this new, real world the world of things in which the plain man finds himself, and in which he has felt so much at home?

A closer scrutiny reveals that the world of atoms and molecules into which the man of science resolves the system of material things is not, after all, so very different in kind from the world to which the plain man is accustomed. He can understand without difficulty the language in which it is described to him, and he can readily see how a man may be led to a.s.sume its existence.

The atom is not, it is true, directly perceivable by sense, but it is conceived as though it and its motions were thus perceivable. The plain man has long known that things consist of parts which remain, under some circ.u.mstances, invisible. When he approaches an object from a distance, he sees parts which he could not see before; and what appears to the naked eye a mere speck without perceptible parts is found under the microscope to be an insect with its full complement of members. Moreover, he has often observed that objects which appear continuous when seen from a distance are evidently far from continuous when seen close at hand. As we walk toward a tree we can see the indefinite ma.s.s of color break up into discontinuous patches; a fabric, which presents the appearance of an unbroken surface when viewed in certain ways may be seen to be riddled with holes when held between the eye and the light. There is no man who has not some acquaintance with the distinction between appearance and reality, and who does not make use of the distinction in common life.

Nor can it seem a surprising fact that different combinations of atoms should exhibit different properties. Have we not always known that things in combination are apt to have different properties from the same things taken separately? He who does not know so much as this is not fit even to be a cook.

No, the imperceptible world of atoms and molecules is not by any means totally different from the world of things in which the plain man lives. These little objects and groups of objects are discussed very much as we discuss the larger objects and groups of objects to which we are accustomed. We are still concerned with _things_ which exist in s.p.a.ce and move about in s.p.a.ce; and even if these things are small and are not very familiarly known, no intellectual revolution is demanded to enable a man to understand the words of the scientist who is talking about them, and to understand as well the sort of reasonings upon which the doctrine is based.

9. MATHEMATICS.--Let us now turn to take a glance at the mathematical sciences. Of course, these have to do with things sooner or later, for our mathematical reasonings would be absolutely useless to us if they could not be applied to the world of things; but in mathematical reasonings we abstract from things for the time being, confident that we can come back to them when we want to do so, and can make use of the results obtained in our operations.

Now, every civilized man who is not mentally deficient can perform the fundamental operations of arithmetic. He can add and subtract, multiply and divide. In other words, he can use _numbers_. The man who has become an accomplished mathematician can use numbers much better; but if we are capable of following intelligently the intricate series of operations that he carries out on the paper before us, and can see the significance of the system of signs which he uses as an aid, we shall realize that he is only doing in more complicated ways what we have been accustomed to do almost from our childhood.

If we are interested, not so much in performing the operations, as in inquiring into what really takes place in a mind when several units are grasped together and made into a new unit,--for example, when twelve units are thought as one dozen,--the mathematician has a right to say: I leave all that to the psychologist or to the metaphysician; every one knows in a general way what is meant by a unit, and knows that units can be added and subtracted, grouped and separated; I only undertake to show how one may avoid error in doing these things.

It is with geometry as it is with arithmetic. No man is wholly ignorant of points, lines, surfaces, and solids. We are all aware that a short line is not a point, a narrow surface is not a line, and a thin solid is not a mere surface. A door so thin as to have only one side would be repudiated by every man of sense as a monstrosity. When the geometrician defines for us the point, the line, the surface, and the solid, and when he sets before us an array of axioms, or self-evident truths, we follow him with confidence because he seems to be telling us things that we can directly see to be reasonable; indeed, to be telling us things that we have always known.

The truth is that the geometrician does not introduce us to a new world at all. He merely gives us a fuller and a more exact account than was before within our reach of the s.p.a.ce relations which obtain in the world of external objects, a world we already know pretty well.

Suppose that we say to him: You have spent many years in dividing up s.p.a.ce and in scrutinizing the relations that are to be discovered in that realm; now tell us, what is s.p.a.ce? Is it real? Is it a thing, or a quality of a thing, or merely a relation between things? And how can any man think s.p.a.ce, when the ideas through which he must think it are supposed to be themselves non-extended? The s.p.a.ce itself is not supposed to be in the mind; how can a collection of non-extended ideas give any inkling of what is meant by extension?

Would any teacher of mathematics dream of discussing these questions with his cla.s.s before proceeding to the proof of his propositions? It is generally admitted that, if such questions are to be answered at all, it is not with the aid of geometrical reasonings that they will be answered.

10. THE SCIENCE OF PSYCHOLOGY.--Now let us come back to a science which has to do directly with things. We have seen that the plain man has some knowledge of minds as well as of material things. Every one admits that the psychologist knows minds better. May we say that his knowledge of minds differs from that of the plain man about as the knowledge of plants possessed by the botanist differs from that of all intelligent persons who have cared to notice them? Or is it a knowledge of a quite different kind?

Those who are familiar with the development of the sciences within recent years have had occasion to remark the fact that psychology has been coming more and more to take its place as an independent science.

Formerly it was regarded as part of the duty of the philosopher to treat of the mind and its knowledge; but the psychologist who pretends to be no more than a psychologist is a product of recent times. This tendency toward specialization is a natural thing, and is quite in line with what has taken place in other fields of investigation.

When any science becomes an independent discipline, it is recognized that it is a more or less limited field in which work of a certain kind is done in a certain way. Other fields and other kinds of work are to some extent ignored. But it is quite to be expected that there should be some dispute, especially at first, as to what does or does not properly fall within the limits of a given science. Where these limits shall be placed is, after all, a matter of convenience; and sometimes it is not well to be too strict in marking off one field from another.

It is well to watch the actual development of a science, and to note the direction instinctively taken by investigators in that particular field.

If we compare the psychology of a generation or so ago with that of the present day, we cannot but be struck with the fact that there is an increasing tendency to treat psychology as a _natural science_. By this is not meant, of course, that there is no difference between psychology and the sciences that concern themselves with the world of material things--psychology has to do primarily with minds and not with bodies. But it is meant that, as the other sciences improve upon the knowledge of the plain man without wholly recasting it, as they accept the world in which he finds himself and merely attempt to give us a better account of it, so the psychologist may accept the world of matter and of minds recognized by common thought, and may devote himself to the study of minds, without attempting to solve a cla.s.s of problems discussed by the metaphysician. For example, he may refuse to discuss the question whether the mind can really know that there is an external world with which it stands in relation, and from which it receives messages along the avenues of the senses. He may claim that it is no more his business to treat of this than it is the business of the mathematician to treat of the ultimate nature of s.p.a.ce.

Thus the psychologist a.s.sumes without question the existence of an external real world, a world of matter and motion. He finds in this world certain organized bodies that present phenomena which he regards as indicative of the presence of minds. He accepts it as a fact that each mind knows its own states directly, and knows everything else by inference from those states, receiving messages from the outer world along one set of nerves and reacting along another set. He conceives of minds as wholly dependent upon messages thus conveyed to them from without. He tells us how a mind, by the aid of such messages, gradually builds up for itself the notion of the external world and of the other minds which are connected with bodies to be found in that world.

We may fairly say that all this is merely a development of and an improvement upon the plain man's knowledge of minds and of bodies.

There is no normal man who does not know that his mind is more intimately related to his body than it is to other bodies. We all distinguish between our ideas of things and the external things they represent, and we believe that our knowledge of things comes to us through the avenues of the senses. Must we not open our eyes to see, and unstop our ears to hear? We all know that we do not perceive other minds directly, but must infer their contents from what takes place in the bodies to which they are referred--from words and actions.

Moreover, we know that a knowledge of the outer world and of other minds is built up gradually, and we never think of an infant as knowing what a man knows, much as we are inclined to overrate the minds of infants.

The fact that the plain man and the psychologist do not greatly differ in their point of view must impress every one who is charged with the task of introducing students to the study of psychology and philosophy.

It is rather an easy thing to make them follow the reasonings of the psychologist, so long as he avoids metaphysical reflections. The a.s.sumptions which he makes seem to them not unreasonable; and, as for his methods of investigation, there is no one of them which they have not already employed themselves in a more or less blundering way. They have had recourse to _introspection_, _i.e._ they have noticed the phenomena of their own minds; they have made use of the _objective method_, i.e. they have observed the signs of mind exhibited by other persons and by the brutes; they have sometimes _experimented_--this is done by the schoolgirl who tries to find out how best to tease her roommate, and by the boy who covers and uncovers his ears in church to make the preacher sing a tune.

It may not be easy to make men good psychologists, but it is certainly not difficult to make them understand what the psychologist is doing and to make them realize the value of his work. He, like the workers in the other natural sciences, takes for granted the world of the plain man, the world of material things in s.p.a.ce and time and of minds related to those material things. But when it is a question of introducing the student to the reflections of the philosophers the case is very different. We seem to be enticing him into a new and a strange world, and he is apt to be filled with suspicion and distrust. The most familiar things take on an unfamiliar aspect, and questions are raised which it strikes the unreflective man as highly absurd even to propose. Of this world of reflective thought I shall say just a word in what follows.

11. REFLECTIVE THOUGHT.--If we ask our neighbor to meet us somewhere at a given hour, he has no difficulty in understanding what we have requested him to do. If he wishes to do so, he can be on the spot at the proper moment. He may never have asked himself in his whole life what he means by s.p.a.ce and by time. He may be quite ignorant that thoughtful men have disputed concerning the nature of these for centuries past.

And a man may go through the world avoiding disaster year after year by distinguishing with some success between what is real and what is not real, and yet he may be quite unable to tell us what, in general, it means for a thing to be real. Some things are real and some are not; as a rule he seems to be able to discover the difference; of his method of procedure he has never tried to give an account to himself.

That he has a mind he cannot doubt, and he has some idea of the difference between it and certain other minds; but even the most ardent champion of the plain man must admit that he has the most hazy of notions touching the nature of his mind. He seems to be more doubtful concerning the nature of the mind and its knowledge than he is concerning the nature of external things. Certainly he appears to be more willing to admit his ignorance in this realm.

And yet the man can hold his own in the world of real things. He can distinguish between this thing and that, this place and that, this time and that. He can think out a plan and carry it into execution; he can guess at the contents of other minds and allow this knowledge to find its place in his plan.

All of which proves that our knowledge is not necessarily useless because it is rather dim and vague. It is one thing to use a mental state; it is another to have a clear comprehension of just what it is and of what elements it may be made up. The plain man does much of his thinking as we all tie our shoes and b.u.t.ton our b.u.t.tons. It would be difficult for us to describe these operations, but we may perform them very easily nevertheless. When we say that we _know_ how to tie our shoes, we only mean that we can tie them.

Now, enough has been said in the preceding sections to make clear that the vagueness which characterizes many notions which constantly recur in common thought is not wholly dispelled by the study of the several sciences. The man of science, like the plain man, may be able to use very well for certain purposes concepts which he is not able to a.n.a.lyze satisfactorily. For example, he speaks of s.p.a.ce and time, cause and effect, substance and qualities, matter and mind, reality and unreality. He certainly is in a position to add to our knowledge of the things covered by these terms. But we should never overlook the fact that the new knowledge which he gives us is a knowledge of the same kind as that which we had before. He measures for us s.p.a.ces and times; he does not tell us what s.p.a.ce and time are. He points out the causes of a mult.i.tude of occurrences; he does not tell us what we mean whenever we use the word "cause." He informs us what we should accept as real and what we should repudiate as unreal; he does not try to show us what it is to be real and what it is to be unreal.

In other words, the man of science _extends_ our knowledge and makes it more accurate; he does not _a.n.a.lyze_ certain fundamental conceptions, which we all use, but of which we can usually give a very poor account.

On the other hand, it is the task of _reflective thought_, not in the first instance, to extend the limits of our knowledge of the world of matter and of minds, but rather _to make us more clearly conscious of what that knowledge really is_. Philosophical reflection takes up and tries to a.n.a.lyze complex thoughts that men use daily without caring to a.n.a.lyze them, indeed, without even realizing that they may be subjected to a.n.a.lysis.

It is to be expected that it should impress many of those who are introduced to it for the first time as rather a fantastic creation of problems that do not present themselves naturally to the healthy mind.

There is no thoughtful man who does not reflect sometimes and about some things; but there are few who feel impelled to go over the whole edifice of their knowledge and examine it with a critical eye from its turrets to its foundations. In a sense, we may say that philosophical thought is not natural, for he who is examining the a.s.sumptions upon which all our ordinary thought about the world rests is no longer in the world of the plain man. He is treating things as men do not commonly treat them, and it is perhaps natural that it should appear to some that, in the solvent which he uses, the real world in which we all rejoice should seem to dissolve and disappear.

I have said that it is not the task of reflective thought, _in the first instance_, to extend the limits of our knowledge of the world of matter and of minds. This is true. But this does not mean that, as a result of a careful reflective a.n.a.lysis, some errors which may creep into the thought both of the plain man and of the scientist may not be exploded; nor does it mean that some new extensions of our knowledge may not be suggested.

In the chapters to follow I shall take up and examine some of the problems of reflective thought. And I shall consider first those problems that present themselves to those who try to subject to a careful scrutiny our knowledge of the external world. It is well to begin with this, for, even in our common experience, it seems to be revealed that the knowledge of material things is a something less vague and indefinite than the knowledge of minds.

II. PROBLEMS TOUCHING THE EXTERNAL WORLD

CHAPTER III

IS THERE AN EXTERNAL WORLD?

12. HOW THE PLAIN MAN THINKS HE KNOWS THE WORLD.--As schoolboys we enjoyed Cicero's joke at the expense of the "minute philosophers."

They denied the immortality of the soul; he affirmed it; and he congratulated himself upon the fact that, if they were right, they would not survive to discover it and to triumph over him.

At the close of the seventeenth century the philosopher John Locke was guilty of a joke of somewhat the same kind. "I think," said he, "n.o.body can, in earnest, be so skeptical as to be uncertain of the existence of those things which he sees and feels. At least, he that can doubt so far (whatever he may have with his own thoughts) will never have any controversy with me; since he can never be sure I say anything contrary to his own opinion."

Now, in this chapter and in certain chapters to follow, I am going to take up and turn over, so that we may get a good look at them, some of the problems that have presented themselves to those who have reflected upon the world and the mind as they seem given in our experience. I shall begin by asking whether it is not possible to doubt that there is an external world at all.

The question cannot best be answered by a jest. It may, of course, be absurd to maintain that there is no external world; but surely he, too, is in an absurd position who maintains dogmatically that there is one, and is yet quite unable to find any flaw in the reasonings of the man who seems to be able to show that this belief has no solid foundation.

And we must not forget that the men who have thought it worth while to raise just such questions as this, during the last twenty centuries, have been among the most brilliant intellects of the race. We must not a.s.sume too hastily that they have occupied themselves with mere trivialities.