Robert Thouless

Dr. Robert H. Thouless

Educated at Corpus Christi College, Cambridge, where he was awarded his PhD in 1922. He then went on to become a Lecturer in Psychology at Manchester, in Glasgow, and again in Cambridge. Here he became the Reader in Educational Psychology. He was President of the British Association's Psychology Section in 1937, and published a number of books connected with this subject. President of the SPR from 1942 till 1944.

The Critics of ESP

 - Robert H. Thouless -

          THE EXPERIMENTAL evidence for the reality of ESP is obviously strong. It is indeed generally agreed that it would be strong enough to create conviction in any other field. There are, however, some who remain unconvinced by this evidence since they find its strength insufficient to outweigh the initial improbability of the organism being able to react to any information that has not come to it through the channels of sense. Those who are thus unconvinced may play a useful part in the development of the research if their doubts lead them to make criticisms that are soundly directed against real weaknesses in the supporting evidence for psi-phenomena. The ideal critic is one who is concerned to make an honest appraisal of the evidence and not merely with making a case against ESP.

Some critics fall far short of this ideal. In their anxiety to make a case against ESP, they may distort evidence, finding fault with experiments as not proving the reality of ESP while ignoring the fact that the experiments in question were not carried out with the intention of providing such evidence and that they would not be appealed to as evidence for the reality of ESP by any research worker in this field. The useful critic is one who recognises that the case for the reality of ESP rests on the strongest evidence provided by the best experiments designed to test this reality, and that, if this case is to be demolished, it must be by finding weaknesses in the evidence from these experiments.

There is a type of criticism, more concerned with establishing a case than with forming a balanced judgment, which is of no help to the research but rather tends to hinder it by diverting the energies of research workers into unprofitable controversy. There are, for example, critics who try to create bias against research findings by the use of such emotional language as 'fairy-land atmosphere' and 'simple credulity'. Still less are the ends of objective assessment of experimental results helped by those who try to create prejudice against psychical researchers by speculating as to unworthy motives for their opinions, or even by digging up or inventing discreditable episodes in their personal lives which have no connection with their experimental researches.

Such crudities are not to be found in the work of the two critics who will be discussed here: Dr G. R. Price of Minnesota and Professor Hansel of Swansea. Although these too sometimes seem to fall short of the standards of the ideal critic, one can, without agreeing with their conclusions, recognise that they are aiming at something essential to the work of psychical research, the testing of its foundations. If these are sound, they will survive the criticism of the honest critic, however searching this may be. Such a critic may also contribute to the research by making experimenters aware of unsuspected weaknesses in their experimental designs. This can be serviceable so long as it does not lead to an extreme preoccupation with experimental precautions which may produce types of experiment that are as unfruitful as they are elaborately safeguarded. Least of all is it desirable that sensitivity to criticism should mislead experimenters into the vain effort to create a new design of experiment that is impervious to all criticism, and away from the more profitable task of finding out about the nature of ESP.

Dr G. R. Price's criticism started from the very reasonable contention that, in a choice between the improbable and the impossible, we must choose the improbable (Price, 1955). Having been, at one time, a believer in ESP, Price changed his mind after reading Hume's discussion of miracles in which it is urged that we should always believe in the knavery or follies of others rather than in events that violate the laws of nature. He was convinced that the best ESP work cannot be accounted for by error and that the odds against their chance occurrence are overwhelming. Therefore one must consider the possibilities of fraud either by the experimenter or by one of those working with him. He takes Dr Soal's experiment as one of those most effectively cutting out all normal means of explanation, and discusses a number of different ways in which the results obtained could have been produced fraudulently. The actual modes of fraud suggested by Price would not be easy since they would involve memorisation of target orders and the use of codes. But Price argues that they would not have been impossible and, since they are merely highly improbable, they are to be preferred as explanations to ESP which he considers to be impossible.

There is, of course, here no assertion that anyone did commit fraud in these experiments. What is asked is the perfectly proper question as to whether anyone (including the experimenters) could have produced the results by fraud. This is a reasonable question to be asked about any experimental results (in other fields of research besides parapsychology) if the reported results seem improbable and the experiment is not easily repeatable. Unless special and unusual precautions have been taken, the answer to this question will generally be 'Yes'. This will not, in the absence of any ground for doubting the reliability of the experimenter, be a reason for rejecting the results of the experiments in question except for those who are convinced that they know the results are impossible. This conviction may be insecurely based but those who hold it will necessarily reject any experiments which point to such results.

Since Price's presuppositions would lead him to reject the results of any experiment in which experimenter fraud was possible, however improbable, there seems to be some inconsistency in his suggestion of a fraud-proof experiment with targets in sealed metal containers and with a jury of twelve prominent persons, all hostile to ESP. If we ignore the difficulty that such a design would seem likely to inhibit ESP, there remains the fatal objection that if this experiment were successful, it too would be inconclusive. It is true that the chance of twelve hostile persons entering into a conspiracy to deceive would be much less than that of two experimenters already favourably impressed by the evidence for ESP. But, although smaller, it would not be zero; if those twelve testified to an impossibility, those who agree with Dr Price would have to reject their evidence on the ground that even a high degree of improbability is to be preferred to an impossibility.

Professor Hansel also, in the Journal of the Society for Psychical Research and in a recent book (1966), has put forward a somewhat similar view. He is rather less emphatic than Price in his rejection of the possibility of ESP but regards its intrinsic improbability as too great for the existing experimental evidence to be sufficient support for its reality. In his opinion, the design of experiments has not excluded the possibility of their results having been fraudulently produced. He has also suggested how fraud could have produced the observed results in the Pearce-Pratt and also in the Soal-Goldney series of experiments.

With respect to the Pearce-Pratt experiment, Hansel points out that, although the percipient was seen to go into the University Library during the experiment, there was no one with him there and he might have left it and looked through the fanlight of Dr Pratt's door and so observed the target cards as they were recorded by Pratt. This is obviously a very unlikely explanation since the risk of his being seen would have been great, and it has been pointed out that the opinion that he could have seen the target cards if he had been looking through the fanlight is based on an incorrect plan of Pratt's room (Stevenson, 1967). It remains true that leaving the percipient by himself in the library was a defect in design of this experiment and leaves open the possibility that Pearce left the library and obtained knowledge of the order of the target cards by means normal but unknown. This is a theoretical possibility even if we think (as I certainly do) that nothing of the sort happened. A simpler explanation of the same kind would he that Pratt and Rhine were in collusion to defraud; the co-operation of Pearce would then not have been necessary.

In the case of the Soal-Goldney experiments, Hansel suggests that the successful agents might have memorised the card order and produced successful results by changing the coding cards so as to produce maximum scores. This too is not likely to be a correct suggestion; it would require a remarkable feat of memory, and it has been pointed out by Soal that even if it were carried out at maximum efficiency, it would not produce a deviation from mean chance expectation as great as that found in the Soal-Goldney experiments (Soal, 1960).

Although, however, the particular suggestions made by Price and Hansel as to how fraud might have produced the results found in these experiments may be erroneous, this would not affect the main point of their criticism. The point is: 'The impossible does not happen. ESP is impossible. Therefore ESP does not happen. If, therefore, any experimental results have been obtained under such carefully controlled conditions that they can be explained only by ESP or by fraud, the explanation by fraud must be accepted however unlikely it may seem to be.' The critic naturally prefers to be able to suggest how the fraud took place, but this is not essential to the argument.

Those who do not accept this argument will not deny its first premise. That the impossible does not happen is a tautology which it would be nonsensical to deny. The second premise that ESP is impossible may reasonably be doubted. Our intuitive judgments as to what is and what is not impossible may indeed merely be habits of thought expressing expectations based on what we already know. The history of scientific advance gives us many examples of such expectations which have been falsified, and those familiar with the history of science are not likely to feel much confidence in their intuitions as to what is and what is not possible. They will be rather inclined to look for a sounder guide in an experimental investigation of what does and what does not happen. What happens must belong to the realm of the possible, whatever may be our feelings as to whether it ought to happen.

But anyone so convinced of the reliability of his own intuitions about the limits of possibility that he can say with confidence that ESP is not possible will not be turned from this opinion merely by evidence derived from one (or more than one) highly successful experiment with new and more rigid safeguards against the possibility of fraud. Nor should he be so converted, for, however elaborate the safeguards, the possibility of collusive fraud is not reduced to zero. Even if Price's experiment were successful with its scaled metal containers and hostile jury, such a critic should still feel bound to prefer an extreme improbability to an impossibility.

We must consider then whether there is not another road to conviction as to the reality of ESP more sure than that of multiplying precautions against the possibility of fraud by the experimenter. I think there is a more hopeful way of achieving this aim which depends on the fact that the one person who knows with certainty whether the experimenter has cheated is the experimenter himself. So, if any person wanting to test the reality of ESP carries out a successful (i.e. highly significant) experiment with full primary precautions (against sensory leakage, recording errors, fraud by percipient, etc.) and he knows that he has not himself cheated, that experiment will be conclusive to him. It may be strong evidence to others as well, but will not be conclusive if they consider the remote possibility that the experimenter has cheated; that possibility will be closed only to the experimenter himself, but to the experimenter it will be closed absolutely.

In carrying out such an experiment I suggest that a simple design of experiment is to be preferred. Full primary precautions are compatible with a simple overall design. The complexities of the Soal-Goldney design were directed towards creating conviction that the experimenters could not be cheating and such precautions will be unnecessary in an experiment whose object is to convince the experimenter himself, It is interesting to note that Hansel's criticism of the Soal-Goldney experiment suggests as a possible means of fraud the five cards used for coding, which was a feature introduced to make it harder for any of the experimental team to cheat. This criticism might be met by the development of a new complication of design that would make the changing of the code cards impossible. This new complication might then, in its turn, be shown to have new possibilities of evasion. I think it is better to stick to simple experimental designs, and to eliminate the possibility of results being produced by the experimenters cheating, not by increased elaboration of design but by providing opportunities for critics to see whether they can, as experimenters, repeat the successes.

I propose to call this the 'Warner way', since it is the method which was followed by Professor Lucien Warner in the experiment described in the last chapter (Warner, 1937). In this experiment, Warner used a percipient who had already shown her ability in ESP, and, with fully adequate primary precautions, obtained a highly significant result. This provided conclusive evidence for the reality of ESP to Warner himself who knew that he had not cheated, and strong evidence for anyone else who believes in Wainer's good faith. It is not, of course, sufficient evidence for the critic who believes that ESP is more unlikely than any alternative explanation. If he is to be convinced, it must be by doing such an experiment himself and doing it successfully. He might, of course, do it and not get a successful result and so find himself confirmed in his scepticism. He would, at any rate, have the satisfaction of knowing that he had taken the risk of being proved wrong. It is not clear how many of the more prominent of the critics of ESP have exposed themselves to this risk.

They may, of course, have wished to do so, but found it too difficult to get the co-operation of a percipient with a previous record of success. I suggest that it would be a good thing for parapsychological laboratories with a good percipient to refrain from the continuous experimenting with them which seems to inhibit their ESP performance. Instead they might be made members of a pool of potential experimental subjects who could be available for short series of experiments by those who were unconvinced of the reality of ESP but were willing to take part in experiments so designed as to give a good chance of success with adequate primary precautions.

It is often overlooked by critics of ESP that many of those who believe in ESP have come to believe in it by the Warner road; they have themselves obtained results under adequately safeguarded conditions and they themselves know they have not cheated. Against their conviction of the reality of ESP, arguments based on the possibility that experimenters carrying out the crucial experiments on ESP could have cheated are ineffective. Their conviction of the reality of ESP does not depend on these experiments.

Although we may doubt the assertions of those who tell us that ESP is impossible, we cannot reasonably deny that its occurrence seems improbable. We have deeply ingrained ways of thinking based on the physical sciences which lead us to expect that no information can pass from one mind to another without passing through the channels of sense, and that no information can be received about events in the outside world unless it passes through these same channels of sense. The type of explanation of transfer of information that science leads us to accept is one in which there is a continuous train of physical events between the thing informed about and the brain receiving the information. Although there is much that is mysterious about normal perception, it is a process that fits the ordinary scientific system of explanation if we ignore the problem of how a physical event in the brain is related to a conscious process. Leaving aside this problem with which science cannot deal, we may explain the process of visual perception as a continuous train of causally connected physical events, starting with a chain of electromagnetic waves from the object which travel to the retina of the observer, there causing a chemical change which produces excitation in the retinal end-organs from which an impulse passes along fibres of the optic nerve to the visual area of the cerebral cortex. There is thus a complete chain of physical causation between the object seen and the brain of the person seeing it, so the pattern of events is one which is recognised as belonging to normal science.

This is plainly not the case in any form of extra-sensory perception. There is no discoverable chain of physical events linking the brain of the agent with that of the percipient in a telepathy experiment. It is true that telepathy can be dealt with in a way in which science has often dealt with in apparent gap in causation, by postulating a physical link where none appears. We may thus suppose that, in telepathy, some form of radiation passes from agent to percipient. In suggesting this, one is following a respectable tradition of stretching existing principles of explanation as far as possible to cover unexpected new facts. But this may not be the right way to deal with them; it may be that what is required is new principles of explanation. In the case of telepathy, Vasiliev has shown that, if there is a radiation carrying information, it is not screened by a thickness of metal plate which we should expect to screen electromagnetic radiation of any likely wave-length (Vasiliev, 1963). This does not disprove the radiation theory of telepathy, but it does suggest very strongly that it is not in this direction that we must look for an explanation. This suggestion is further strengthened by the consideration that any explanation in terms of emitted radiations can only be applied with great difficulty to cases of clairvoyance and not at all to phenomena of precognition since the percipient cannot be supposed to be receiving radiations emitted by something which does not yet exist. There is a strong case for considering that what is required for explanation is not a new application of present explanatory principles but rather the development of new explanatory principles.

The difficulty of such a development is considerably exaggerated by Price when he refers to ESP as a violation of nature and classes it with such events as miracles. This view, which treats an incompatibility with current scientific theory as equivalent to a breach of nature, seems to assume a somewhat superstitious view of natural law. A natural law is not a preexisting system of rules which phenomena have to obey; it is a system of rules that the scientist puts forward to account for observed regularities. If an unexpected event occurs, it is not a breach of the law; it is an indication that the law, as at present enunciated, must be altered. Our expectations have been based on laws which are imperfect.

That any existing system of laws may be imperfect and in need of amendment is not an unfamiliar situation in the history of science; it happens at all those turning points in scientific development which have been called by Professor Kuhn 'scientific revolutions' (Kuhn, 1962). Examples of such turning points are the passage from Ptolemaic to Copernican cosmology, from Lamarckian to Darwinian views of organic development, from Newtonian to relativity dynamics, etc. In all these cases, expectations based on a currently accepted system of concepts and laws have been found not to accord with observation and have been replaced by a system of expectations based on a new set of concepts and laws; in Kuhn's terms, on a new 'paradigm'.

The situation which in the past has led to the overthrow of an accepted paradigm and its replacement by a new one, is the discovery in the course of normal research that some fact or facts revealed by research are not such as the old paradigm would lead us to expect. These may be called anomalies; examples are to be found in the failure of the Michelson-Morley experiment to detect ether drift due to the Earth's motion through space, Planck's discovery of unexpected irregularities in black box radiation (leading to the quantum theory), the discovery of diffraction fringes which amongst other things led to the general acceptance of the wave theory of light, and so on. In all science, the turning up of an experimental result that would not have been predicted from existing ways of thinking is important as a challenge to those ways of thinking. This is what gives ESP its theoretical importance; it is clearly an anomaly in the sense that it does not fit in with our currently accepted explanations of behaviour as influenced by the external environment only so far as this environment creates physical stimuli which act on our sense organs. The situation is one that the history of science would lead us to expect to be the starting point of a scientific revolution. it may be many years before the direction of this revolution can be clearly seen.

Kuhn's theory of scientific revolutions contains many illuminations of the problems of parapsychology; amongst others it suggests why we should expect to have critics who deny the reality of the phenomena reported in our experiments and why they will not be convinced merely by increased weight of experimental evidence. He points out that practitioners of normal science have always tended to resist new theories because these seem to throw doubt on what they are doing and on what they have already done. He also suggests that this resistance to change by normal science has its own value in emphasising the fact of anomaly when a new finding does not fit normal expectations. But this resistance has always led a number of the practitioners of normal science to refuse to recognise the necessity for conceptual change. They will not indeed abandon an old paradigm until a new paradigm is ready to take its place. We are, in parapsychology, far from the situation of being able to formulate a new paradigm. So we must expect incredulity to persist among our critics, and not expect that this incredulity will be overcome by mere increase of experimental evidence obtained under new conditions of stringency.

This does not mean that parapsychologists should now abandon experimental work and devote themselves to thinking out a new body of theory. It is not in that way that new paradigms have developed in scientific history. Rather it has happened that increased knowledge through research has shown increased discrepancy between what is observed and what existing theories would predict. Then, as these anomalies increase, at a certain stage of the resulting tension, someone comes along with a new paradigm which relieves the tension by showing that the apparent anomalies are, in the new way of looking at the field, no longer anomalies but are exactly what one would expect.

It seems to me that we are not yet at that stage of tension in parapsychology at which a new paradigm can be promulgated, and that we can only reach that stage by much more research. One obvious difference between parapsychology and the physical sciences is that expectations can be much more precisely formulated in the physical sciences and that one can therefore more precisely state the nature of the contradiction between what is observed and what is expected, and more easily formulate the nature of the paradigm change that will make this contradiction disappear. In order to get more precise research results in parapsychology we need more reliable methods of getting experimental results. The effort to get such reliable experimental results, whether by selection or by training of percipients, seems to be one of the most important immediate objectives of research in parapsychology.

In the meantime, the fact of anomaly is strongly indicated, not only in the experimental demonstration of the reality of ESP, but also in that of other paranormal phenomena which will be discussed later, particularly in precognition and psycho-kinesis. The situation is not one, I think, that invites us to theoretical speculation, but rather one that invites us to keep our minds open to the necessity for theoretical change and also to the fact that similar theoretical changes have taken place frequently during the development of science. It is not a situation that should surprise us or that should be seen as a threat to science. At the same time, it is not a situation that offers us much hope of being able to anticipate the nature of the paradigm change when it comes. What is required from us is flexibility of mind and readiness to accept paradigm change. When the time is ripe, the work of Kuhn suggests that the individual who introduces the new paradigm will be young or new to the field. Many of us are neither, so we should not be tempted to see ourselves as the Einsteins of parapsychology, but rather as having the task of preparing his way by increasing knowledge of the field.


HANSEL, C. E. M. (1966), "ESP: a Scientific Evaluation", London.

KUHN, T. S. (1962), "The Structure of Scientific Revolutions", Chicago.

PRICE, G. R. (1955), 'Science and the Supernatural', Science, 26 April (abstracted Journal of Parapsychology, xix 1955, 238-41).

SOAL, S. G. (1960), 'A reply to Mr. Hansel', Proceedings of the Society for Psychical Research, xiiii, 43-82.

STEVENSON, I. (1967), 'An Antagonist's View of Parapsychology', Journal of the American Society for Psychical Research, 254-67.

VASILIEV, L. L. (1963), "Experiments in Mental Suggestion" (English translation), Church Crookham.

WARNER, L. (1937), 'A Test Case', J. Parapsych., i, 234-8.


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