Chapter XXX: Section 25: (c) Skepticism

Hume’s skepticism is directly connected with the subject of the preceding chapter, but wants still a few words for itself. Though it is not the lawyer’s problem to take an attitude with regard to philosophical skepticism, his work becomes essentially easier through the study of Hume’s doctrines.

According to these, all we know and infer, in so far as it is unmathematical, results from experience, and our conviction of it and our reasoning about it, means by which we pass the bounds of sense-perception, depend on sensation, memory and inference from causation. Our knowledge of the relation of cause and effect results also from experience, and the doctrine, applied to the work of the criminalist, may be formulated as follows: “Whatever we take as true is not an intellectual deduction, but an empirical proposition.” In other words, our presuppositions and inferential knowledge depend only upon those innumerable repetitions of events from which we postulate that the event recurred in the place in question. This sets us the problem of determining whether the similar cases with which we compare the present one really are similar and if they are known in sufficiently large numbers to exclude everything else.

Consider a simple example. Suppose somebody who had traveled all through Europe, but had never seen or heard of a negro, thought about the pigmentation of human beings: neither all his thinking nor the assistance of all possible scientific means can lead him to the conclusion that there are also black people--that fact he can only discover, not think out. If he depends only on experience, he must conclude from the millions of examples he has observed that all human beings are white. His mistake consists in the fact that the immense number of people he has seen belong to the inhabitants of a single zone, and that he has _failed to observe_ the inhabitants of other regions.

In our own cases we need no examples, for I know of no inference which was not made in the following fashion: “The situation was so in a hundred cases, it must be so in this case.” We rarely ask whether we know enough examples, whether they were the correct ones, and whether they were exhaustive. It will be no mistake to assert that we lawyers do this more or less consciously on the supposition that we have an immense collection of suggestive a priori inferences which the human understanding has brought together for thousands of years, and hence believe them to be indubitably certain. If we recognize that all these presuppositions are compounds of experience, and that every experience may finally show itself to be deceptive and false; if we recognize how the actual progress of human knowledge consists in the addition of one hundred new experiences to a thousand old ones, and if we recognize that many of the new ones contradict the old ones: if we recognize the consequence that there is no reason for the mathematical deduction from the first to the hundred-and-first case, we shall make fewer mistakes and do less harm. In this regard, Hume[135] is very illuminative.

According to Masaryk,[136] the fundamental doctrine of Humian skepticism is as follows: “If I have had one and the same experience ever so often, i.e., if I have seen the sun go up 100 times, I expect to see it go up the 101st time the next day, but I have no guarantee, no certainty, no evidence for this belief. Experience looks only to the past, not to the future. How can I then discover the 101st sunrise in the first 100 sunrises? Experience reveals in me the habit to expect similar effects from similar circumstances, but the intellect has no share in this expectation.”

All the sciences based on experience are uncertain and without logical foundation, even though their results, as a whole and in the mass, are predictable. Only mathematics offers certainty and evidence. Therefore, according to Hume, sciences based on experience are unsafe because the recognition of causal connection depends on the facts of experience and we can attain to certain knowledge of the facts of experience only on the ground of the evident relation of cause and effect.

This view was first opposed by Reid, who tried to demonstrate that we have a clear notion of necessary connection. He grants that this notion is not directly attained either from external or internal experience, but asserts its clearness and certainty in spite of that fact. Our mind has the power to make its own concepts and one such concept is that of necessary connection. Kant goes further and says that Hume failed to recognize the full consequences of his own analysis, for the notion of causality is not the only one which the understanding uses to represent a priori the connection of objects. And hence, Kant defines psychologically and logically a whole system of similar concepts. His “Critique of Pure Reason” is intended historically and logically as the refutation of Hume’s skepticism. It aims to show that not only metaphysics and natural science have for their basis “synthetic judgments a priori,” but that mathematics also rests on the same foundation.

Be that as it may, our task is to discover the application of Hume’s skepticism to our own problems in some clear example. Let us suppose that there are a dozen instances of people who grew to be from 120 to 140 years old. These instances occur among countless millions of cases in which such an age was not reached. If this small proportion is recognized, it justifies the postulate that nobody on earth may attain to 150 years. But now it is known that the Englishman Thomas Parr got to be 152 years old, and his countryman Jenkins was shown, according to the indubitable proofs of the Royal Society, to be 157 years old at least (according to his portrait in a copper etching he was 169 years old). Yet as this is the most that has been scientifically proved I am justified in saying that nobody can grow to be 200 years old. Nevertheless because there are people who have attained the age of 180 to 190 years, nobody would care to assert that it is absolutely impossible to grow so old. The names and histories of these people are recorded and their existence removes the great reason against this possibility.

We have to deal, then, only with greater or lesser possibilities and agree with the Humian idea that under similar conditions frequency of occurrence implies repetition in the next instance. Contrary evidence may be derived from several so-called phenomena of alternation. E. g., it is a well known fact that a number in the so-called Little Lottery, which has not been drawn for a long time, is sure finally to be drawn. If among 90 numbers the number 27 has not turned up for a long time its appearance becomes more probable with every successive drawing. All the so-called mathematical combinations of players depend on this experience, which, generalized, might be held to read: the oftener any event occurs (as the failure of the number 27 to be drawn) the less is the probability of its recurrence (i.e., it becomes more probable that 27 will be drawn)--and this seems the contrary of Hume’s proposition.

It may at first be said that the example ought to be put in a different form, i.e., as follows: If I know that a bag contains marbles, the color of which I do not know, and if I draw them one by one and always find the marble I have drawn to be white, the probability that the bag contains only white ones grows with every new drawing that brings a white marble to light. If the bag contains 100 marbles and 99 have been drawn out, nobody would suppose that the last one would be red--for the repetition of any event increases the probability of its occurrence.

This formulation proves nothing, inasmuch as a different example does not contradict the one it is intended to substitute. The explanation is rather as follows: In the first case there is involved the norm of equal possibilities, and if we apply the Humian principle of increase of probability through repetition, we find it effective in explaining the example. We have known until now always that the numbers in the Little Lottery are drawn equally, and with approximate regularity,--i.e., none of the single numbers is drawn for a disproportionately long time. And as this fact is invariable, we may suppose that every individual number would appear with comparative regularity. But this explanation is in accord with Hume’s doctrine.

The doctrine clarifies even astonishing statistical miracles. We know, e.g., that every year there come together in a certain region a large number of suicides, fractures of arms and legs, assaults, unaddressed letters, etc. When, now, we discover that the number of suicides in a certain semester is significantly less than the number in the same semester of another year, we will postulate that in the next half-year a comparatively larger number of suicides will take place so that the number for the whole year will become approximately equal. Suppose we say: “There were in the months of January, February, March, April, May and June an average of x cases. Because we have observed the average to happen six times, we conclude that it will not happen in the other months but that instead, x+y cases will occur in those months, since otherwise the average annual count will not be attained.” This would be a mistaken abstraction of the principle of equal distribution from the general Humian law, for the Humian law applied to this case indicates: “For a long series of years we have observed that in this region there occur annually so and so many suicides; we conclude therefore that in this year also there will occur a similar number of suicides.”

The principle of equal distribution presents itself therefore as a subordinate rule which must not be separated from the principal law. It is, indeed, valid for the simplest events. When I resolve to walk in x street, which I know well, and when I recall whether to-day is Sunday or a week day, what time it is and what the weather is like, I know quite accurately how the street will look with regard to the people that may be met there, although a large number of these people have chosen the time accidentally and might as well have passed through another street. If, for once, there were more people in the street, I should immediately ask myself what unusual event had taken place.

One of my cousins who had a good deal of free time to dispose of, spent it for several months, with the assistance of his comrade, in counting the number of horses that passed daily, in the course of two hours, by a café they frequented. The conscientious and controlled count indicated that every day there came one bay horse to every four. If then, on any given day, an incommensurably large number of brown, black, and tawny horses came in the course of the first hour, the counters were forced to infer that in the next 60 minutes horses of a different color must come and that a greater number of bays must appear in order to restore the disturbed equilibrium. Such an inference is not contradictory to the Humian proposition. At the end of a series of examinations the counters were compelled to say, “Through so many days we have counted one bay to every four horses; we must therefore suppose that a similar relationship will be maintained the next day.”

So, the lawyer, too, must suppose, although we lawyers have nothing to do with figures, that he knows nothing a priori, and must construct his inferences entirely from experience. And hence we must agree that our premises for such inferences are uncertain, and often subject to revision, and often likely, in their application to new facts, to lead to serious mistakes, particularly if the number of experiences from which the next moment is deduced, are too few; or if an unknown, but very important condition is omitted.

These facts must carefully be kept in mind with reference to the testimony of experts. Without showing ourselves suspicious, or desirous of confusing the professional in his own work, we must consider that the progress of knowledge consists in the collection of instances, and anything that might have been normal in 100 cases, need not in any sense be so when 1000 cases are in question. Yesterday the norm may have been subject to no exception; to-day exceptions are noted; and to-morrow the exception has become the rule.

Hence, rules which have no exceptions grow progressively rarer, and wherever a single exception is discovered the rule can no longer be held as normative. Thus, before New Holland was discovered, all swans were supposed to be white, all mammals incapable of laying eggs; now we know that there are black swans and that the duck-bill lays eggs. Who would have dared to assert before the discovery of the X-ray that light can penetrate wood, and who, especially, has dared to make generalizations with regard to the great inventions of our time which were not afterwards contradicted by the facts? It may be that the time is not too far away in which great, tenable and unexceptionable principles may be posited, but the present tendency is to beware of generalizations, even so far as to regard it a sign of scientific insight when the composition of generally valid propositions is made with great caution. In this regard the great physicians of our time are excellent examples. They hold: “whether the phenomenon A is caused by B we do not know, but nobody has ever yet seen a case of A in which the precedence of B could not be demonstrated.” Our experts should take the same attitude in most cases. It might be more uncomfortable for us, but certainly will be safer; for if they do not take that attitude we are in duty bound to presuppose in our conclusions that they have taken it. Only in this wise, by protecting ourselves against apparently exceptionless general rules, can our work be safely carried on.

This becomes especially our duty where, believing ourselves to have discovered some generally valid rule, we are compelled to draw conclusions without the assistance of experts. How often have we depended upon our understanding and our “correct” a priori method of inference, where that was only experience,--and such poor experience! We lawyers have not yet brought our science so far as to be able to make use of the experience of our comrades with material they have reviewed and defined in writing. We have bothered a great deal about the exposition of some legal difficulty, the definition of some judicial concept, but we have received little instruction or tradition concerning mankind and its passions. Hence, each one has to depend on his own experience, and that is supposed to be considerable if it has a score of years to its back, and is somewhat supplemented by the experience, of others. In this regard there are no indubitable rules; everybody must tell himself, “I have perhaps never experienced this fact, but it may be that a thousand other people have seen it, and seen it in a thousand different ways. How then, and whence, my right to exclude every exception?”

We must never forget that every rule is shattered whenever any single element of the situation is unknown, and that happens very easily and frequently. Suppose that I did not have full knowledge of the nature of water, and walked on terra firma to the edge of some quiet, calm pool. When now I presume: water has a body, it has a definite density, it has consistency, weight, etc., I will also presume that I may go on walking over its surface just as over the surface of the earth,--and that, simply because I am ignorant of its fluidity and its specific gravity. Liebman[137] summarizes the situation as follows. The causal nexus, the existential and objective relation between lightning and thunder, the firing of powder and the explosion, are altogether different from the logical nexus, i.e. the mere conceptual connection between antecedent and consequent in deduction. This constitutes the well known kernel of Humian skepticism. We must keep in mind clearly that we never can know with certainty whether we are in possession of all the determining factors of a phenomenon, and hence we must adhere to the only unexceptionable rule: _Be careful about making rules that admit of no exceptions_. There is still another objection to discuss, i.e. the mathematical exception to Humian skepticism. It might be held that inasmuch as the science of justice is closely related in many ways to mathematics, it may permit of propositions a priori. Leibnitz already had said, “The mathematicians count with numbers, the lawyers with ideas,--fundamentally both do the same thing.” If the relationship were really so close, general skepticism about phenomenal sciences could not be applied to the legal disciplines. But we nowadays deal not with concepts merely, and in spite of all obstruction, Leibnitz’s time has passed and the realities of our profession, indeed its most important object, the human being itself, constitute an integrating part of our studies. And the question may be still further raised whether mathematics is really so exempt from skepticism. The work of Gauss, Lobatschewski, Bolyai, Lambert, would make the answer negative.

Let us, for once, consider what significance mathematical postulates have. When Pythagoras discovered his proposition in such a way that he first drew a right-angled triangle and then built a square on each of the sides, and finally measured the area of each and compared them, he must at first have got the notion that that also might be merely accidental. If he had made the construction 10 or 100 times with various triangles and these had resulted always identically, only then might he have been justified in saying that he had apparently discovered a theorem. But then his process was just as thoroughly experiential as that of a scientist who says that a bird has never yet been observed to give birth to living young, and that hence all birds lay eggs.

But Pythagoras did not proceed in this experiential manner in the discovery of his theorem. He constructed and he counted, and when he did that he acted on postulates: “If this is a right-angled triangle and if that be a square, so,”--and this is just what is done in every science. The general propositions are, “If the relations remain the same as formerly the moon must rise to-morrow at such and such a time.” “If this step in a deduction is not false, if it is well grounded at this point, if it really refers to x, it follows....” In his procedures the criminalist does exactly the same thing. What he must be skeptical about is the postulates from which he starts.