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  [Illustration: CLEVER HANS]




  CLEVER HANS

  (THE HORSE OF MR. VON OSTEN)

  _A CONTRIBUTION TO EXPERIMENTAL
  ANIMAL AND HUMAN
  PSYCHOLOGY_

  BY
  OSKAR PFUNGST

  WITH AN INTRODUCTION BY PROF. C. STUMPF,
  AND ONE ILLUSTRATION AND FIFTEEN FIGURES

  TRANSLATED FROM THE GERMAN
  BY
  CARL L. RAHN
  _Fellow in Psychology in the University of Chicago_

  WITH A PREFATORY NOTE BY
  JAMES R. ANGELL
  _Professor of Psychology in the University of Chicago_

  [Illustration]

  NEW YORK
  HENRY HOLT AND COMPANY
  1911




  COPYRIGHT, 1911,
  BY
  HENRY HOLT AND COMPANY




PREFATORY NOTE

[BY JAMES R. ANGELL]

_The University of Chicago_


It gives me great pleasure to accept the invitation of the publishers to
write a word of introduction for Mr. Rahn's excellent translation of
"Der Kluge Hans", a book which in the original has been but little known
to American readers. The present wave of interest in animal life and
behavior renders its appearance peculiarly appropriate.

No more remarkable tale of credulity founded on unconscious deceit was
ever told, and were it offered as fiction, it would take high rank as a
work of imagination. Being in reality a record of sober fact, it verges
on the miraculous. After reading Mr. Pfungst's story one can quite
understand how sedate and sober Germany was for months thrown into a
turmoil of newspaper debate, which for intensity and range of feeling
finds its only parallel in a heated political campaign. That the subject
of the controversy was the alleged ability of a trained horse to solve
complex arithmetical problems may excite gaiety and even derision, until
one hears the details. Scientists and scholars of the highest eminence
were drawn into the conflict, which has not yet wholly subsided,
although the present report must be regarded as quite final in its
verdict.

As for Hans himself, he has become the prototype of a host of less
distinguished imitators representing every level of animal life, and
when last heard from he was still entertaining mystified audiences by
his accomplishments.

But the permanent worth of the book is not to be found in its record of
popular excitement, interesting as that is. It is a document of the very
first consequence in its revelation of the workings of the animal mind
as disclosed in the horse. Animal lovers of all kinds, whether
scientists or laymen, will find in it material of greatest value for the
correct apprehension of animal behavior. Moreover, it affords an
illuminating insight into the technique of experimental psychology in
its study both of human and animal consciousness. Finally, it contains a
number of highly suggestive observations bearing on certain aspects of
telepathy and muscle-reading. All things considered, it may fairly be
said that few scientific books appeal to so various a range of interests
in so vital a way.

Readers who wish to inform themselves of all the personal circumstances
in the case may best read the text just as it stands. Those who desire
to get at the pith of the matter without reference to its historical
settings, may be advised to omit the Introduction by Professor Stumpf of
the University of Berlin, together with supplements II, III and IV.




CONTENTS


                                                           PAGE
  PREFATORY NOTE (By JAMES R. ANGELL)                         v

  INTRODUCTION (By C. STUMPF)                                 1


  CHAPTER
  I. THE PROBLEM OF ANIMAL CONSCIOUSNESS AND "CLEVER HANS"   15

  II. EXPERIMENTS AND OBSERVATIONS                           30

  III. THE AUTHOR'S INTROSPECTIONS                           88

  IV. LABORATORY TESTS                                      102

  V. EXPLANATION OF THE OBSERVATIONS                        141

  VI. GENESIS OF THE REACTION OF THE HORSE                  212

  CONCLUSION                                                240


  SUPPLEMENTS:

  I. MR. VON OSTEN'S METHOD OF INSTRUCTION (By C. STUMPF)   245

  II. THE REPORT OF SEPTEMBER 12th, 1904                    253

  III. AN ABSTRACT FROM THE RECORDS OF THE
  SEPTEMBER-COMMISSION                                      255

  IV. THE REPORT OF DECEMBER 9th, 1904                      261


  TABLE OF REFERENCES                                       267




INTRODUCTION

[BY C. STUMPF]


A horse that solves correctly problems in multiplication and division by
means of tapping. Persons of unimpeachable honor, who in the master's
absence have received responses, and assure us that in the process they
have not made even the slightest sign. Thousands of spectators,
horse-fanciers, trick-trainers of first rank, and not one of them during
the course of many months' observations are able to discover any kind of
regular signal.

That was the riddle. And its solution was found in the unintentional
minimal movements of the horse's questioner.

Simple though it may seem, the history of the solution is nevertheless
quite complex, and one of the important incidents in it is the
appearance of the zooelogist and African traveler, Schillings, upon the
scene, and then there is the report of the so-called Hans-Commission of
September 12, 1904. And finally there is the scientific investigation,
the results of which were published in my report of December 9, 1904.

After a cursory inspection during the month of February, I again called
upon Mr. von Osten in July, and asked him to explain to Professor
Schumann and me just what method he had used in instructing the horse.
We hoped in this way to gain a clue to the mechanism of Hans's feats.
The most essential parts of the information thus gleaned are summarized
in Supplement I. Mr. Schillings came into the courtyard for the first
time about the middle of July. He came as skeptical as everyone else.
But after he, himself, had received correct responses, he too became
convinced, and devoted much of his time to exhibiting the horse, and
daily brought new guests. To be perfectly frank, at the time this seemed
to us a disturbing factor in the investigation, but now we see that his
intervention was a link in the chain of events which finally led to an
explanation. For it was through him that the fact was established beyond
cavil, that the horse was able to respond to strangers in the master's
absence. Heretofore, this had been noted only in isolated cases. Since
it could not be assumed that a well-known investigator should take it
upon himself to mislead the public by intentionally giving signs, the
case necessarily from that time on appeared in the eyes of others in a
light quite different from that in which ordinary circus-tricks would
appear, to which it bore such a striking external resemblance. No matter
how this state of affairs may have arisen in the course of years, no
matter how it might eventually be explained,--the quality of the
extraordinary would necessarily attach itself to this particular case,
as it did.

Of course, to many persons in the interested public the result was
merely that Schillings, also, was placed in the category of deceivers.
On the other hand there were reputable scientists who could not dispose
of the matter in that fashion, and these now openly took their stand
with Schillings and declared that they believed in the horse's ability
to think. Zooelogists especially, saw in von Osten's results evidence of
the essential similarity between the human and the animal mind, which
doctrine has been coming more and more into favor since the time of
Darwin. Educators were disposed to be convinced, on account of the
clever systematic method of instruction which had been used and which
had not, till then, been applied in the education of a horse. In
addition, there were many details which, it seemed, could not be
explained in any other way. So far as I myself was concerned, I was
ready to change my views with regard to the nature of animal
consciousness, as soon as a careful examination would show that nothing
else would explain the facts, except the assumption of the presence of
conceptual thinking. I had thought out the process hypothetically, i. e.,
how one might conceive of the rise of number concepts and arithmetical
calculation along the peculiar lines which had been followed in Hans's
education, and on the basis of the assumption that the beginnings of
conceptual thinking are present in animals. Also, I had too much faith
in human nature to fear lest nothing peculiarly human should remain
after the art of handling numbers should be shown to be common property
with the lower forms. But under no circumstances would I have undertaken
to make a public statement in favor of any particular view in this
extraordinary case, before a thorough investigation, in accordance with
scientific principles, had been made. I expressed this sentiment at the
time, and recommended the appointment of an investigating commission (in
the "Tag" of September 3, 1904).

The purpose of this commission was misunderstood, and therefore many
were disappointed with the report which it published, (Supplement II).
Some had been expecting a positive conclusive explanation; the
commission recommended further investigation. Some had asked for a
solution of the question whether or not the horse was able to think; the
commission maintained neither the one, nor the other. Some had indicated
as the main condition of a satisfactory investigation, that both Mr. von
Osten and Mr. Schillings be excluded from the tests; this was not done.

But the commission--which, by the way, did not give itself this name,
since it had been delegated by no one--undoubtedly had the right to
formulate its problem as it saw fit, and this was carefully expressed at
the beginning of its report as follows: "The undersigned came together
for the purpose of investigating the question whether or not there is
involved in the feats of the horse of Mr. von Osten anything of the
nature of tricks, that is, intentional influence or aid on the part of
the questioner." It was this preliminary question, and not whether or
not the horse could think, which the commission intended to answer. They
proposed to act as a sort of court of honor for the two gentlemen who
had been attacked. It is only in this light that even the _raison
d'etre_ of this body can be understood; for a scientific commission
composed of thirteen men, possessed of varying degrees of scientific
preparation, would have been an absurd travesty, and it will readily be
seen why the two men, who had been attacked, should not be excluded,
since it was they, and primarily Mr. von Osten, upon whom the
observations were to be made.

To be sure the commission did go one step beyond that which it had
proposed to itself, since it added that it believed that unintentional
signs of the kind which are at present familiar, were also excluded.
This led many to the unwarranted conclusion that the commission had
declared that Hans was able to think. Whereas the thing which might have
been logically suggested was that instead of the assumption of the
presence of independent thinking, the commission may have had in mind
unintentional signs of a kind hitherto unknown. I explained this to a
reporter of the "Frankfurter Zeitung" (Mr. A. Gold), who had come to me
for information, and in his article he made this hypothesis appear as
the most probable one.[A] Certain statements of the circus-manager
Busch, who speaks of a 'connection' of some sort, go to show that other
members of the commission held to the view just stated.

    [Footnote A: "Frankfurter Zeitung" of September 22, 1904:
    "Concerning the question whether the horse was given some sort of
    aid, Professor Stumpf expressed himself freely. He said: 'We were
    careful to state in our report that the intentional use of the
    (actual) means of training, on the part of the horse's teacher, is
    out of the question,... nor are there involved any of the known
    kinds of unconscious, involuntary aids. Our task was completed after
    we had ascertained that no tricks or aids of the traditional sort
    were being employed'." After some remarks on unconscious habituation
    and self-training on the part of animals, the writer arrives at the
    conclusion that "the horse of Mr. von Osten has been educated by its
    master in the most round-about way, in accordance with a method
    suited for the development of human reasoning powers, hence in all
    good faith, to give correct responses by means of tapping with the
    foot. But what the horse really learned by this wearisome process
    was something quite different, something that was more in accord
    with his natural capacities,--he learned to discover by purely
    sensory aids which are so near the threshold that they are
    imperceptible for us and even for the teacher, when he is expected
    to tap with his foot and when he is to come to rest."]

But how did it come to pass that the commission should deny completely
the presence of intentional signals, while, as regards the unintended,
it excluded only those which were of the known sort? The report clearly
shows that the decision as to the absence of voluntary signals was
based not merely upon the fact that no such signals had been detected by
the most expert observers, but also upon the character of the two men
who exhibited the horse, upon their behavior during the entire period,
and upon the method of instruction which Mr. von Osten had employed. In
the case of unintentional signs, on the other hand, one had to deal with
the fact with which physiologists and experimental psychologists are
especially familiar, viz., that our conscious states, without our
willing it--indeed, even in spite of us--are accompanied by bodily
changes which very often can be detected only by the use of extremely
fine graphic methods. The following is a more general instance: every
mother, who detects the lie or divines the wish in the eyes of the
child, knows that there are characteristic changes of facial expression,
which are, nevertheless, very difficult of definition.[B]

    [Footnote B: "From the productions of the 'thought-readers' we see
    how slight and seemingly insignificant the unconscious movements may
    be, which serve as signs for a sensitive re-agent. But in this case
    no contact is necessary. There would have to be some sort of visible
    or audible expression on the part of the questioner. No proof for
    this has as yet been advanced."

    How any one possessing the power of logical thought could possibly
    infer from these words of mine (published in the above-mentioned
    article in the "Tag"), that I denied the possibility of the
    occurrence of visual signs, is to me incomprehensible. What I did
    deny, and still deny, is that up to that time any had been proven to
    occur.]

The commission did not even maintain or believe that unintentional signs
within the realm of the senses known to us, were to be excluded.
Professor Nagel and I would never have subscribed to any such
conclusion. The sentence in question, therefore, could only be
interpreted as follows: that signals of the kind that are used
intentionally in the training of horses, could not have occurred even
as unintended signs, for otherwise Mr. Busch would have detected them.
And in order to be observed by him it was immaterial whether they were
given purposely or not. The same signs, therefore, which as a result of
his observations were declared not to be present, could not be assumed
to be involved as unintentional.

For my part I am ready to confess that at this time I did not expect to
find the involuntary signals, if any such were involved, in the form of
movements. I had in mind rather some sort of nasal whisper such as had
been invoked by the Danish psychologist A. Lehmann, in order to explain
certain cases of so-called telepathy. I could not believe that a horse
could perceive movements which escaped the sharp eyes of the
circus-manager. To be sure, extremely slight movements may still be
perceived after objects at rest have become imperceptible. But one would
hardly expect this feat on the part of an animal, who was so deficient
in keenness of vision, as we have been led, by those of presumably
expert knowledge, to believe of the horse,--one would expect it all the
less because Mr. von Osten and Mr. Schillings would move hither and
thither in most irregular fashion while the horse was going through his
tapping, and would therefore make the perception of minute movements all
the more difficult.

Nor was there anything in the exhibitions given at the same time in a
Berlin vaudeville by the mare "Rosa," which might have shattered this
belief. For, in the case of this rival of Hans, the movements involved
were comparatively coarse. The closing signal consisted in bending
forward on the part of the one exhibiting the mare, while up to that
point he had stood bolt upright. Most persons were not aware of this,
because this change in posture cannot be noticed from the front. I
happened to sit to the side and caught the movement every time. It was
the same that was noted by Dr. Miessner, another member of the
commission, (see page 256), but concerning which he did not give me a
more complete account. Later I learned through Professor Th. W.
Engelmann that the very same movement was employed not long ago, for
giving signals to a dog exhibited at Utrecht. This particular movement
is very well adapted to commercial purposes, since the spectator always
tries to view the performance from a point as nearly in front of the
animal and its master as possible, thus making the detection of the
trick all the more difficult.

The details of the various experiments made by this commission are given
in an excerpt from the records kept by Dr. von Hornbostel, which I
showed to a small group of persons a few days after the 12th of
September (Supplement III). At that time none of the particulars was
published, because the commission wished to wait until some positive
statement might be made. The public was merely to be assured that a
group of reputable men, from different spheres of life, who could have
no purpose in hazarding their reputation, believed that the case was one
worthy of careful investigation.

I left Berlin on September 17th and did not return until October 3d. In
the meantime Mr. Schillings continued the investigation, and was
assisted in part by Mr. Oskar Pfungst, one of my co-workers at the
Psychological Institute. For the first time a number of tests were now
made in which neither the questioner, nor any of those present knew the
answer to the problem. Such tests naturally were the first steps toward
a positive investigation. The results were such that Mr. Schillings was
led to replace his hypothesis of independent conceptual thinking by one
of some kind of suggestion. In this he was strengthened somewhat by
having noted the fact that in his questions which he put to the horse,
he might proceed as far as to ask the impossible. He has always been
ready to offer himself in the tests which have been undertaken since
then.

On October 13, 1904, together with the two gentlemen mentioned in the
beginning of my report, I began my more detailed investigation, and
finished on November 29. We worked for several hours on the average of
four times each week. I take this opportunity of giving expression of
the recognition which is due to the two gentlemen. They were ready to go
to the courtyard in all kinds of weather, at times they went without me,
and they always patiently discussed the order and method of the
experiments and the results. Dr. von Hornbostel had the important task
of keeping the records, and Mr. Pfungst undertook the conduct of the
experiments. It was he, who, soon after the blinder-tests disclosed the
necessary presence of visual signs, discovered the nature of these
signs. Without him we might have shown the horse to be dependent upon
visual stimuli in general, but we never would have been able to gain
that mass of detail, which makes the case valuable for human psychology.
But I am tempted to praise not merely his patience and skill, but also
his courage. For we must not believe that Mr. von Osten's horse was a
"perfectly gentle" animal. If he stood untied and happened to be excited
by some sudden occurrence, he would make that courtyard an unsafe place,
and both Mr. Schillings and Mr. Pfungst suffered from more than one
bite. In this connection I would also express my obligations to Count
Otto zu Castell-Ruedenhausen, for his frequent intercession on our behalf
with the owner of the horse, and for his many evidences of good-will and
helpfulness.

After the publication of this report (Supplement IV), there was still
some further discussion of the case in societies of various kinds and in
the press, but no important objections were raised. A hippologist
thought that men of his calling should have been consulted, a
telepathist believed that telepathists should have been called in. There
was also some further talk of suggestion, will-transference,
thought-reading and the occult, but no attempt was made to elucidate
these vague terms with reference to their application to the case in
hand. Others adhered to the old cry of "fraud," for a share of which Mr.
Pfungst now fell heir. There were a few who felt it incumbent upon
themselves to preserve their 'priority,' and therefore stated with a
show of satisfaction that I had finally 'confessed' myself to hold their
respective points of view. As if there were anything like "confessions"
in science! As if mere affirmations, even though sealed and deposited in
treasure vaults, had any value with reference to a case in which every
manner of supposition had been advanced in lieu of explanation. Why did
they wait so long, if they had convincing proof for their position?

And finally there were disappointed Darwinists who expressed fear lest
ecclesiastical and reactionary points of view should derive favorable
material from the conclusions arrived at in my report. Needless fear.
For lovers of truth it must always remain a matter of inconsequence
whether anyone is pleased or displeased with the truth, and whether it
is enunciated by Aristotle or Haeckel.

Mr. von Osten, however, continued to exhibit Hans, and is probably doing
so still, but in what frame of mind, I dare not judge. The spectators
continue to look on, they are doubly alert to catch movements, and many
of them have learned from Mr. Schillings what kind of movements they are
to expect. But these "initiated" ones regularly return and declare that
there is nothing in the movements and that they simply could not
discover any aids given to the horse. Nothing can so well show how
difficult the case is, and how great the need of a thorough exposition
of the whole matter, than the account given in the following pages of
Mr. Pfungst. Its publication has been delayed on account of the
additional tests made in the laboratory, but we have reason to suppose
that through these additional tests the work has gained in permanent
value. Experimental psychologists will perhaps be greatly interested in
the graphic registration of the minute involuntary movements which
accompany the thought process, and in the artificial association of a
given involuntary movement with a given idea. Likewise the tests on
sense-perception in horses, which have led to essential changes in
hitherto current views, and the critical review of the comprehensive
literature on similar achievements of other animals, will be welcomed by
many.

Before closing these introductory remarks, I would make one more
statement concerning Mr. von Osten. The reader will notice that the
judgment passed upon him in this treatise is placed at the end, whereas
in the report of the commission it came first. This was brought about by
the change that was made in the way of stating the problem. Then the
question discussed was whether 'tricks' were involved; now the question
is: What is the mechanism of the process? The question of the good faith
of the master was taken up once more only because the facts that were
brought to light by the later experimentation seemingly brought forward
new grounds for distrust. But by placing this discussion toward the end
of our report we wished to indicate that everything that is said of the
present status of facts, is quite independent of the view taken
concerning Mr. von Osten. Even assuming that the horse had been
purposely trained by him to respond to this kind of signal, the case
would still deserve a place in the annals of science. For visual signs,
planned and practiced so that they could not only be more readily
perceived by the animal than by man, but could be transferred from their
inventor to others without any betrayal of the secret,--this would be an
extraordinary invention, and Mr. von Osten would then be a fraud, but
also a genius of first rank.

In truth he probably was neither, but I was brief in my report, for
otherwise I would have been obliged to go into more detail than the case
warranted. And a judgment passed upon a human personality is quite a
different matter from a judgment upon a horse. If it is unscientific to
make unqualified statements concerning a horse after the performance of
only a few experimental tests, it is certainly an unwarranted thing to
pass a moral judgment upon a man upon the basis of meagre material.
Anyone who would assume the role of judge should bear in mind that here
too we have more than a hundredfold the material which they could bring
forward, and among it some which, if taken alone, would be more
unfavorable than any that they had. But here all things should be
weighed together, and not in isolation. A former instructor of
mathematics in a German gymnasium, a passionate horseman and hunter,
extremely patient and at the same time highly irrascible, liberal in
permitting the use of the horse for days at a time and again tyrannical
in the insistence upon foolish conditions, clever in his method of
instruction and yet at the same time possessing not even the slightest
notion of the most elementary conditions of scientific procedure,--all
this, and more, goes to make up the man. He is fanatic in his
conviction, he has an eccentric mind which is crammed full of theories
from the phrenology of Gall to the belief that the horse is capable of
inner speech and thereby enunciates inwardly the number as it proceeds
with the tapping. From theories such as these, and on the basis of all
sorts of imagined emotional tendencies in the horse, he also managed to
formulate an explanation for the failure of the tests in which none of
the persons present knew the answer to the problem given the horse, and
also for the failure of those tests in which the large blinders were
applied. And he would often interfere with or hinder other tests which,
according to his point of view, were likely to lead us astray. And yet,
when the first tests with the blinders did turn out as unmistakably
sheer failures, there was such genuine surprise, such tragi-comic rage
directed against the horse, that we finally believed that his views in
the matter would be changed beyond a doubt. "The gentlemen must admit,"
he said at the time, "that after seeing the objective success of my
efforts at instruction, I was warranted in my belief in the horse's
power of independent thought." Nevertheless, upon the following day he
was as ardent an exponent of the belief in the horse's intelligence as
he ever had been.

And finally, after I could no longer keep from him the results of our
