The phenomena in question fall into two broad groups. Extra-sensory perception, also known as anomalous cognition, includes telepathy, clairvoyance, and precognition. Anomalous operation includes psychokinesis (in the past referred to as telekinesis), out-of-body experiences, near-death experiences, and reincarnation. The general term "psi phenomena" (or the somewhat older term, "psychic phenomena") covers all of these categories.
The standing of the field of parapsychology has always been controversial within the broader spectrum of science, and perhaps even more bitterly so today than in the past. The controversy tends to take center stage, at least in discussions taking place outside the field, and so there is an entire section of this article devoted to aspects of this debate, to give some idea of the critique of the field by its detractors, and of the counter arguments by its defenders. Other subarticles describe some of the history of the field and the current state of (claims of) the field.
As the word for the field indicates, parapsychology is sometimes considered a sub-branch of psychology, and this arose historically since it involves the study of apparently mental faculties. In its modern form, parapsychology is an interdisciplinary field, which has attracted physicists, engineers, and biologists as well as psychologists and those from the softer sciences, many of whom have less regard for the mental aspects than an interest in the implications for all fields if psi phenomena should ever gain widespread acceptance. As a result, many people are not satisfied with the term, and have proposed alternatives, such as "psi research" (similar to the older term "psychic research"), but for better or worse parapsychology is the term that has the greatest acceptance today.
The controversy surrounding parapsychology comprises many issues, and debate is ongoing in most of them. The following subsections present some of the larger issues.
A minority of critics believe that it is impossible in principle to approach the study of paranormal phenomena in a scientific manner, much as it would be impossible to scientifically prove or disprove the existence of a deity. Obviously parapsychologists disagree, and it is probably safe to say that even most critics of the field agree that the truth of the matter, whatever it may be, will eventually yield to the scientific method.
A larger minority of critics hold that, while a scientific approach to the topic is in theory possible, the state of practice in the field doesn't yet meet their criteria for "good science", and as such it should be considered a pseudoscience. They accuse parapsychologists as being alternately (a) frauds[?], (b) incompetent, (c) naive and therefore easily deceived by fraudulent subjects, or (d) some combination of the above.
Parapsychologists disagree with this assessment, as most of them were trained in one scientific field or another and are familiar with scientific methods. They exploit all the usual machinery that other branches of science use: testing hypotheses and predictions with experimental protocols; publishing experimental details and data in peer-reviewed periodicals and conferences; attempts to replicate experiments at other labs; giving and taking critical feedback with resulting improvement of methods, etc.
Certainly parapsychology as a field has not been warmly embraced by the mainstream of science, at least not by its gatekeepers, i.e. those who control funding, promotion, and publication at the mainstream institutions and journals. Attitudes of the rank and file scientists towards parapsychology is less clear since surveys targeting this group are far less common than those targeting the general population. In his article Save Our Science: Paranormal Phenomena and Zetetics (http://www.unice.fr/zetetique/anglais/a_zetetique.html), skeptic Henri Broch bemoans,
And sociologist Andrew Greeley, studying available surveys and polls since 1978, found that not only did the percentage of Americans admitting to psychic experiences increase over a decade, about two thirds of college professors accepted ESP, and more than 25% of "elite scientists" believed in ESP. Other polls have shown that many scientists hold such beliefs privately but do not share such opinions publicly (or at least not in their professional circles) for fear of ridicule or worse. If anything, the data suggest that on average, scientists are at least as accepting as the general population of paranormal phenomena and thus of parapsychology as a valid field for scientific study.
The Parapsychological Association is an affiliate of the American Association for the Advancement of Science (AAAS). There are chairs, centers, or research units concerned with parapsychology in whole or in part at many universities around the world, as well as independent laboratories involved in parapsychology. And from time to time even prominent skeptics have participated in the design and execution of parapsychological experiments. It seems that the field of parapsychology has some degree of general acceptance, in the sense that its topic is amenable to scientific study in theory and at least some of its practitioners in fact use sound scientific methods, even if there is no agreement about the results of the field to date.
It is worth noting that the ranks of parapsychologists do include skeptics, for example Chris French and his colleagues at the Anomalistic Psychology Research Unit at Goldsmiths University of London, and Richard Wiseman and his colleagues at the Perrott-Warrick Research Unit in the Psychology Department of the University of Hertfordshire, both of which units are affiliates of the Parapsychological Association. These researchers do not approach the field with a belief in the paranormal, but are rather interested in the purely psychological aspects of those who report paranormal experiences, along with the study of the psychology of deception, hallucination, etc. These researchers also have provided their own guidelines and input to other parapsychologists for the design of experiments and how to properly test those who claim psychic abilities.
By far the most consistently and hotly debated issue is the interpretation of the existing body of evidence that the field of parapsychology has gathered to date.
At one extreme, some critics judge that the quality of the entire body of evidence to date is so poor that essentially the field has nothing to show for its entire history. At the other extreme, some believers in the paranormal believe that scientific study of paranormal phenomena, i.e. parapsychology, is redundant and completely unecessary. In the spectrum of views in between, some consider that the existence of certain psi phenomena has now been well established by the scientific evidence; others consider that none of the evidence is anywhere near so definitive, though perhaps some of the evidence is intriguing enough to warrant further study.
Criticisms of work in the field cover a wide range, from the general to the specific, for example:
Responses from parapsychologists to some of these criticisms include:
The opinion of parapsychologists regarding the overall evaluation of the body of evidence to date is divided. As noted above, some parapsychologists are skeptics and do not believe that there is anything observed so far which cannot ultimately be explained by normal means. Probably a majority of parapsychologists belive in the likelihood, or at least the possibility, of actual psi phenomena, though there is a range of attitudes toward the evidence.
Some parapsychologists agree with critics that the field has not yet reached the degree of consistent repeatability of experimental results needed for general consensus. John Beloff, for example, in his book Parapsychology: A Concise History, notes the evanescent -- some have said the apparently evasive -- nature of psychic phenomena over time, and that the range of phenomena observable in a given era seems to be culturally dependent. For example, in earlier times, psychic research studied macro physical phenomena demonstrated by spiritualist mediums which, according to the reports passed down to us in the literature, far surpassed anything that any of today's "psychics" can demonstrate. Skeptics consider this more evidence of the non-existence of psi phenomena. Yet many people, such as Beloff, cannot easily dismiss the entirety of all the positive accounts, so many of which came from the experts of their day (including scientists and conjurors), many of whom began as noted skeptics, and so believe that continued research in the field is justified.
Other parapsychologists, such as Dean Radin[?] and supporters such as statistician Jessica Utts[?], take the stance that the existence of certain psi phenomena has been reasonably well established in recent times through repeatable experiments that have been replicated dozens to hundreds of times at labs around the world. They refer to meta-analyses of psi experiments that conclude that the odds against chance (null hypothesis) of experimental results far exceeds that commonly required to establish results in other fields, sometimes by orders of magnitude. Indeed, many parapsychologists have moved on from proof-oriented research intented primarily to establish the existence of psi phenomena to "process-oriented" research intended to explore the parameters of psi phenomena. Time will tell whether these results prove to be evanescent as well.
Magician James Randi demands that magicians as well as scientists be included as observers of psychic experiments, to help detect trickery. Professional magicians such as Randi have claimed that the feats performed by people who claim to be psychics can also be achieved by concealed and fraudulent physical manipulation; Randi, Penn & Teller, and other stage magicians often publicly perform such tricks in public, and then explain how they are done.
Parapsychologists note that some parapsychologists are also magicians, and parapsychologists as a group already do in fact work with input from skeptics and fellow parapsychologists alike to continually improve their experimental protocols to continue to reduce the likelihood of fraud or unintentional error. Also, many modern parapsychologists do not study "people who claim to be psychics", so the feats of such claimants are largely irrelevant to their research.
The James Randi Educational Foundation (http://www.randi.org/) offers a one million U.S. dollars prize to anyone who can demonstrate any psychic or paranormal phenomenon. The foundation has set up a program wherein it approves the test proposed by the parapsychologist, but doesn't itself judge the results. No one has ever collected the prize. While skeptics make much of Randi's Challenge, many parapsychologists question the sincerity of Randi's offer, and in any case they generally pay little attention to it.
The offering of prizes for demonstrations isn't new to the field. Circa 1924, Scientific American magazine offered a $5000 prize to anyone who could produce any "visible psychic manifestation". Medium Mina Crandon, known in the literature as "Margery", made a bid and was tested by a committee set up by the editorial staff. Her performance was such that the committee members were split in their opinions. The magazine published the mixed report in its November 1924 issue, no prize was awarded, and the competition was declared closed the following year. In the early 1900s, the then well-known stage magician and skeptic Howard Thurston was sufficiently impressed by the demonstrations of medium Eusapia Palladino that he advertised in the New York Times his offer of $1000 to charity in the name of any fellow conjuror who could duplicate the feats of Ms. Palladino under similar conditions. He had no takers.
There are a variety of other objections to parapsychology as well.