Everybody normally acts on the assumption that the value of human
testimony is an extremely variable quantity. The rules by which we
assess the value of testimony, in the ordinary affairs of life, are of
that thoroughly habitual kind that hardly involve conscious processes;
they repose on two judgments, which we are always making. Our belief in
direct testimony to an event is conditioned by the nature of the event
and by our estimate of the “personal equation” of the witness. These
two factors are not quite independent; it is very seldom, for instance,
that we attribute “general untrustworthiness” to anybody who is known
to us. Our experience usually teaches us that there are certain classes
of statements--e.g. his breaks at billiards, the number of miles
his motor-car runs on a gallon of petrol--for which that particular
witness’s credibility is at a minimum. For some other classes of
statements we may have learnt to take his word without hesitation. What
the mathematicians call the “credibility” of a witness is not, in the
case of any witness of whom we have personal knowledge, a constant
figure. It varies with the event, often in an extremely complicated
way. When Brown is listening to Jones talking about the enormities of
Smith the extremely delicate and rapid weighing of probabilities being
performed by Brown beggars any mathematical description. When the
witness is personally unknown to us the matter becomes simpler. Our
conclusions, one way or another, will be held with less confidence, but
they will be more simply arrived at. We may, on the evidence supplied
by the testimony itself--the tone of the letter, the man’s manner in
the dock--class the witness as a man of a certain type. Corresponding
to each type we have a rough scale of credibility for different types
of events. In cases where we know nothing of the witness beyond his
bare statement that he witnessed the occurrence of the event our
estimate of his credibility is based on very general and usually
rather vague considerations. We are guided by two things: the initial
credibility of the event and our estimate of the general value of human
testimony. Both of these criteria, and in particular the second, are
excessively ill-defined.
In the first place, what do we mean by the initial credibility
of an event? There are very few cases where this notion can be
precisely defined. The simple instances dealt with in the elements of
mathematical probability do, it is true, permit of precise definition.
The chance that a white ball will be drawn from an urn containing
five black balls and one white ball can be exactly estimated, for we
are in possession of all the very simple relevant factors. But the
probability that Romulus founded Rome obviously belongs to a very
different category. And what is the initial credibility of a miracle?
Hume, as is well known, thought that the _a priori_ incredibility
of a miracle was so great that its occurrence could not be established
by human testimony. He is here trying to establish a ratio between the
initial credibility of a class of events and the initial credibility
of human testimony to such events. He is taking some kind of average
in both cases, but it is difficult to see how such an average can
be arrived at. Vague considerations of this kind are of no value in
forming conclusions on matters of real interest to us, although they
may be sufficient to warrant a lazy scepticism regarding what William
James calls “dead hypotheses,” or may form the basis for amusing and
ingenious mathematical exercises. But we have no notion of an average
initial credibility which is of any use in practice; each case must
be judged on its own merits. And if, to take the second point, we
reached some average for the value of human testimony in general, we
should never, in practice, apply it. The utmost we can hope to do is
to establish a more or less constant relation between the testimony
of classes of witnesses and classes of events. We have to divide
witnesses into types, and for each given type estimate the value of
its testimony to different classes of events. We must investigate the
difference it makes when the witness is taken as isolated and when he
is taken as a member of a group of witnesses. In this way we may hope
to reach results which are of value in judicial procedure, in the study
of history, and in various particular investigations, including those
modern substitutes for miracles, the phenomena of spiritualism. We
are, in fact, to investigate man in his capacity as a truth-recording
instrument.
The result of such researches as have been made may be said, briefly,
to show that human testimony has much less value than is normally
assigned to it and, in particular, much less value than it is held to
possess in a Court of Law. The experimental results obtained in this
field are, indeed, often startling. It is hardly too much to say that
one’s first impulse, on becoming acquainted with the results hitherto
reached, is to fall back on a general and dismayed scepticism regarding
the value of human testimony to anything whatever. But a closer
examination of the results show us that this attitude is unwarranted,
and reinforces the common-sense assumption that the value of human
testimony is a matter of degree, varying from complete worthlessness
to a very fair presumption that the event occurred as stated. The
investigation is useful chiefly in showing us what factors influence
this value.
It is convenient to separate out these factors according to the scheme
recently employed by Dr. Edmond Locard, in his analysis of police
records over a number of years. The statements made by a witness
repose, in the first place, on sensations which he has experienced. It
might be thought too obvious to be worth mentioning that we require
the witness who heard a sound, for instance, to have reasonably
good hearing, and yet there are many cases where simple preliminary
considerations of this kind are not taken into account. Professor
Zöllner’s famous book _Transcendental Physics_, for instance,
alleged marvels that occurred in the presence of Slade, the medium;
and these alleged marvels, of great influence in spreading a belief
in spiritualism, were witnessed to by four professors, Zöllner,
Fechner, Scheibner and Weber. But a member of the Seybert Commission,
Mr. George S. Fullerton, as a result of personal interviews, found
that two of these professors, Fechner and Scheibner, were partially
blind at the time. Their sensations, therefore, in this respect, were
untrustworthy. But defects of this kind may usually be determined and
this factor conditioning the witnesses’ credibility allowed for. Where
a witness makes appeal to a sensation which may be checked the check
should always be imposed. Thus Dr. Locard gives an instance where a
witness stated that an event occurred in a mill at a certain hour.
How did he know the hour? By hearing a clock strike at the time the
event occurred. A test was made, and it was found that the noise of
the mill made the striking of the clock quite inaudible. The witness
then remembered that he did not hear the clock strike until he had
left the mill. Similarly, witnesses have testified that they saw a man
leave a doorway, their post of observation being one from which the
doorway could not be seen. Sensations may often be checked, however,
and, to a careful inquirer, they need not be a grave source of error.
But the next stage is concerned with the witness’s perceptions. Of his
sensations he will single some out for attention and neglect the rest.
He singles out those which, for some reason or another, interest him
most. It may quite easily happen, therefore, that the sensations most
relevant to the inquiry in hand have been neglected. They have been
filtered, as it were, through the medium of the witness’s interest;
and it is often the case that his interest has not been excited by the
sensations most pertinent to the subsequent inquiry. It is on this fact
that conjurers very largely depend for their success. The attention
of the audience is distracted; they are invited to dismiss certain
sensations as being of no importance, and, in general, it is remarkably
easy to ensure this distraction of attention. Dr. Hodgson’s case of the
English officer and the Hindu juggler well illustrates this point:
Referring to the movements of the coins, he said that he had taken a
coin from his own pocket and placed it on the ground himself, yet
that this coin had indulged in the same freaks as the other coins.
His wife ventured to suggest that the juggler had taken the coin and
placed it on the ground, but the officer was emphatic in repeating
his statement, and appealed to me for confirmation. He was, however,
mistaken. I had watched the transaction with special curiosity, as I
knew what was necessary for the performance of the trick. The officer
had apparently intended to place the coin upon the ground himself, but
as he was doing so the juggler leant slightly forward, dexterously and
in a most unobtrusive manner received the coin from the fingers of the
officer, as the latter was stooping down, and laid it close to the
others. If the juggler had not thus taken the coin, but had allowed
the officer himself to place it on the ground, the trick, as actually
performed, would have been frustrated.
Now I think it highly improbable that the movement of the juggler
entirely escaped the perception of the officer; highly improbable,
that is to say, that the officer was absolutely unaware of the
juggler’s action at the moment of its happening; but I suppose that,
although an impression was made on his consciousness, it was so slight
as to be speedily effaced by the officer’s _imagination_ of
himself as stooping and placing the coin upon the ground.
We have here an instance of erroneous testimony by a witness to his own
actions; testimony to the actions of other people is usually much less
trustworthy. In this matter of direct perception we may discriminate
still further. Tactile perceptions are of almost no value whatever. If
a witness be blindfolded and asked to determine, by touch alone, the
nature, the volume and the material of an object, it will be found that
the responses are very inaccurate. Experience of tactile sensations is
relatively small and deductions therefrom are practically valueless.
Thus the shock of a bullet entering the body may be interpreted as a
slight blow, several dagger thrusts in the back as one thrust, and so
on. A piece of ice drawn across the neck of a blindfolded man and warm
water simultaneously poured on his chest have been stated to cause
death by fright, the man having previously been informed that he was
going to have his throat cut. Perceptions of odour or of taste are even
less trustworthy; and here the difficulty of expression in precise
terms, in the lack of a precise vocabulary, is complicated by the fact
that the witness primarily perceives odours and tastes as pleasant or
unpleasant, and pays attention only to that aspect of them. In cases of
poisoning, therefore, evidence of this kind should be given very little
value.
It is only when we come to the senses of hearing and of sight that
we enter the region where perceptions may have evidential value. In
the case of hearing, however, we must still proceed very warily.
Experiment has shown that estimates of direction, for example, are
quite valueless, since the different estimates made by different
observers obey the laws of pure chance. Training can do a little, but
very little, to render these perceptions more trustworthy; in general,
however, evidence as to the direction of a sound may be neglected.
Estimates of the distance of a sound, also, are of very small value.
The intensity of a heard sound depends on the intensity of the source,
and also on its distance; and these two factors may be apportioned
by the observer in the most arbitrary manner. In the case where the
sound is articulate, as in overhearing a conversation, we are in the
presence of still other sources of error, due to illegitimate inference
and the association of ideas. For words which are not heard will be
supplied by the witness in all good faith. He will have a theory of
the purport of the conversation, and will arrange the sounds he heard
to fit it. Edgar Allen Poe’s example, in _The Murders in the Rue
Morgue_, of the cries of an ape which were interpreted as remarks
in different languages by different observers, is judged by Dr. Locard
to be not at all fantastic. The same general source of error applies
to visual perceptions. Not everything is observed, and the lacunæ
are filled in by the witness in what seems to him the most probable
manner. Oversights in proof-reading furnish a familiar example of this
kind of error. But psychological experiments have produced much more
striking examples. Claparède arranged for a man, wearing the mask of
a clown, to enter his lecture room while a lecture was in progress.
The students were afterwards asked to pick out this mask from a series
of ten, and out of twenty-three who attempted the task five only
were successful--and even these successes were probably due, largely
or wholly, to chance. The appreciation of distances, measured by the
eye, is also very likely to be erroneous, the rule being that large
distances are under-estimated and small ones over-estimated. A similar
rule holds good of estimations of intervals of time. Errors of this
kind are not pure errors of perception; they are due chiefly to lack
of experience. A carpenter or builder would usually make a much more
accurate estimate of the dimensions of, say, the side of a house than
would the ordinary person; and astronomers who work with transit
instruments have, as a class, very accurate perceptions of small
intervals of time. It is chiefly lack of experience, also, which is
responsible for the absurdly different estimates different observers
will make of the number of people in a crowd. Dr. Locard states that,
on questioning the policemen employed to keep order during a procession
as to the number of people they estimated to be taking part in the
procession, he obtained the figures five thousand, ten thousand,
twenty-four thousand. The actual number, he states, was three thousand.
And during another procession two middle-aged, intelligent, educated
Paris journalists gave as their estimates for the number of people
engaged, the one thirty thousand and the other three hundred thousand.
But now let us suppose that our witness, through the medium of his
imperfect senses and his partial attention, has received a certain
image. What deformations may it suffer before it is produced as his
evidence? If his memory of the incident has “lapsed” the image will
undergo comparatively little alteration, but if it has often been
called to mind it will probably suffer a very considerable change.
Each time the image is recalled it will suggest others; the creative
imagination gets to work, altering the emphasis, adding particulars,
obliterating others, and the result will be as much a work of art
as the reproduction of a fact. This tendency is particularly to be
noticed with women, and with certain “excitable” types; it may be
almost a national characteristic, as with Gascons and Sicilians. But
all witnesses are prone to this kind of inaccuracy. Where the event has
often been narrated by the witness the deformations become even more
serious. For he is here exposed not only to the suggestions of his own
creative imagination, but to the suggestions of other people. Every one
wishes to make a success of the story he is telling, and the perception
of what points to stress and what details to add is wonderfully ready
and alert. It has often happened that a witness of perfect good faith
has changed from the simple spectator of a drama to a prominent actor
in it under the influence of repeated narration. Finally, we reach
the point when the witness has to bear his formal testimony. His
observations were imperfect, he has imperfectly remembered them, his
imagination has distorted them, and he is now to express them. A very
considerable additional source of inaccuracy is likely to enter here.
The witness probably cannot express his complete image--words may not
be sufficiently precise to render the fine shades of his remembered
perceptions. The nature of a sound, the kind of emotion expressed by
a voice,--he may have no words for such things. And, in any case,
the witness will not express his complete image. He will select--in
accordance with his own estimate of what is pertinent and what trivial.
He will do this even if he be allowed to talk to his heart’s content;
but the method of question and answer as pursued in our Law Courts
leads to even more imperfect expression. For he is forced to be precise
where his recollection is vague, and he will either give a false
precision to his answer or else profess complete ignorance. More often
still the witness sins by exaggeration, and these exaggerations, in a
thousand subtle ways, usually tend to add to his own importance. And
it is important to notice that, besides tending to import fictitious
details, the witness will tend to exaggerate his degree of conviction.
Where he was originally doubtful he is now perfectly sure.
So far we have been considering the witness in isolation, and we have
not considered the reaction upon his testimony of the emotional state
produced in him by the event. Yet the emotions accompanying the event
have a great bearing upon the value of the witness’s testimony. During
the war it was noticed that the evidence of soldiers freshly wounded
was often of the most fantastic description. They would testify to
the details of catastrophes which had never occurred; they would
assert that so-and-so had been decapitated in front of their eyes, and
so-and-so buried by an explosion, when, as a matter of fact, nothing
remotely resembling these events had taken place. And, under the
influence of the comparatively slighter emotions of a spiritualistic
séance, people will identify the same “materialised” mask as the
features of their husbands, wives, sons, daughters. Under the influence
of such emotions it may be taken as a general rule that perceptions
deteriorate, and illegitimate inference, “unconscious reasoning,”
becomes more marked. Unconscious reasoning, indeed, plays a very great
part in nearly all cases of mal-observation. It is well exemplified
in the statement of the man sitting in a dark wood: “That dog’s bark
is not really a grasshopper, it is the squeaking of a cart.” And Dr.
Locard tells of one experiment he made, while in the Army, with a
barometer which bore a remote resemblance to a clock. His suggestion
that it was a clock was invariably accepted, even by the most eminent
people, and several of them acquired their knowledge of the time of
day from its indications, even when the hour so indicated was highly
improbable. The testimony of great and commanding figures, even to
the time of day, may therefore be open to suspicion. But the immense
part played by unconscious reasoning is best seen in the psychology
of conjuring, under which head it is fair to group the great majority
of alleged spiritualistic phenomena. In this latter case we have
further to recognise what Freud calls the “pleasure-pain principle,”
as distinguished from the “reality-principle.” In other words, the
witnesses are seldom disinterested; they strongly desire to witness
certain events rather than others, and in such cases the slightest
suggestion is sufficient to produce conviction.
When the witness is not isolated, but is a member of a group, the
defects we have before noted, due to the creative imagination, are
likely to be accentuated. The event will have been discussed and a
uniform version gradually prepared. It is almost impossible, from
the unanimous testimony of a number of witnesses who have been in
consultation, to extract the original perceptions. The phenomenon of
_mimétisme testimonial_ makes its appearance, and may assume
abnormal dimensions. A kind of collective hysteria may be induced, and
there can be little doubt that some of the collective denunciations of
witches which took place in the Middle Ages were manifestations of this
form of mimicry.
Such are some of the results that have been reached by the modern
investigations of the value of human testimony. They tell us little
we did not know before, for mankind has had an immense experience of
human testimony; but they make our knowledge more precise and enable us
to see what kinds of testimony are most open to suspicion. The effect
of these researches on judicial procedure should be considerable, and
their influence on the study of history not less marked. On this latter
subject their influence can only be indirect, and in the direction,
probably, of throwing still more doubt on the accuracy of historical
records. The “credibility” of a witness still remains a vague quantity,
but the chances are that it is something less than the value hitherto
assigned to it. The investigation can claim no such precise results
as those enunciated by Craig in 1699 in his _Theologiæ Christianæ
Principia mathematica_, where, after proving that the suspicions of
any history vary in the duplicate ratio of the times taken from the
beginning of the history, he shows that faith in the Gospel, so far as
it depended on oral tradition, expired about the year 880, and, so far
as it depended on written tradition, would expire in the year 3150. The
new investigations of the value of human testimony start from humbler,
but surer, foundations.
_Printed in Great Britain by_ Butler & Tanner, _Frome and
London_
=TRANSCRIBER’S NOTES=
Simple typographical errors have been silently corrected; unbalanced
quotation marks were remedied when the change was obvious, and
otherwise left unbalanced.
Punctuation, hyphenation, and spelling were made consistent when a
predominant preference was found in the original book; otherwise they
were not changed.