"A UFO is an unidentified flying object which has been identified as a possible or actual alien spacecraft. Such objects include meteors, disintegrating satellites, flocks of birds, aircraft, lights, weather balloons, and just about anything within the visible band of electromagnetism. So far, however, nothing has been positively identified as an alien spacecraft in a way required by common sense and science. That is, there has been no recurring identical UFO experience and there is no physical evidence in support of either a UFO flyby or landing.

There are as many photographs of UFOs as there are of the Loch Ness Monster, and they are of equal quality: blurs and forgeries. Other physical evidence, such as alleged debris from alien crashes, or burn marks on the ground from alien landings, or implants in noses or brains of alien abductees, have turned out to be quite terrestrial, including forgeries. The main reasons for believing in  UFOs are the testimony of many people, the inability to distinguish science fiction from science, the ability to trust incompetent men telling fantastic stories, the ability to distrust all contrary sources as being part of an evil conspiracy to withhold the truth, and a desire for contact with the world above. In short, belief in UFOs is akin to belief in God."

From: UFO's - The Skeptics Dictionary, by Robert Todd Carroll

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Phil Klass

Philip Klass, an electrical engineer by education and once the editor of the popular "Aviation Week", is today's most famous skeptic having authored five books on UFOs and appeared on television countless times. In his first book, "UFOs - Identified" published in 1968, Klass suggested that, although terrestrial of origin, many reported UFOs were strong evidence of a new natural phenomenon which was similar in some ways to ball lightning. His subsequent books then revealed a complete reversal in his thinking. Klass had now adopted the position (curiously, this "change of heart" occured after his hypothesis on plasma balls had been thoroughly discredited and rejected by scientists) that the entire UFO phenomenon (including those cases Klass first thought to be accurate and evidence for new phenomena) was the result of, among others, hoaxes, and observational mistakes. 

> An Interview with Philip J. Klass, the World's Leading UFO Skeptic by Gary P. Posner

AGAINST PHIL KLASS

> Phil Klass vs. the "UFO Promoters" by Jerome Clark

Dr. Donald Menzel (1901-1976) was a prominent Harvard astronomer, serving as a professor of both astronomy and of astrophysics. He was also the chairman of Harvard College Observatory from 1954 to 1966. Menzel was a globally renowned astronomer, participating in numerous international committees, leading solar eclipse expeditions, and establishing solar observatories. Menzel also debunked UFOs, authoring three books on the subject: Flying Saucers (1953); The World of Flying Saucers (1964); and The UFO Enigma: A Definitive Explanation of the UFO Phenomenon (1977).  Menzel's disdain for the UFO subject and his published works have been used by skeptics Phil Klass and Robert Sheaffer as evidence that there is nothing to UFOs, yet neither of them has ever responded to the large number of detailed and destructive published criticisms on Menzel's UFO writings, they simply seem to ignore them. 

AGAINST DR. DONALD MENZEL

> Dr. Menzel's interesting background 
> Dr. Menzel's untenable explanations for UFO reports

A member of CSICOP's UFO subcommittee and author of several UFO debunking books. As with Klass, Sheaffer remains vociferously active in this department. Jerome Clark suggests one assess Sheaffer's arguments "in the context of his ferocious hostility to UFOs in general." And adds that Sheaffer feels that "sympathetic consideration of UFO sightings" is not only "irrational" but threatens a "new dark age." UFOlogy of any sort, even a cautious methodological variety is, in Sheaffer's estimation and his italics, "fundamentally a reaction against science and reason." 

AGAINST ROBERT SHEAFFER

> Ohio [Portage County] Police Chase 
> McMinville Oregon photos

Michael Shermer is the publisher of Skeptic magazine, the director of the Skeptics Society, the host of the Skeptics Lecture Series at Caltech, and an adjunct professor at Occidental College. He is the author of Why People Believe Weird Things (W. H. Freeman) that was widely and positively reviewed and was on the Los Angeles Times bestseller list as well as nominated as one of the top 100 notable books of 1997.

> Skeptic.org

Skeptical Arguments & Articles

The Black Box Approach to UFO Perceptions
by James E. Oberg

Discussion on Bruce Maccabee's paper, "UFOs: FANTASY OR PRESENT REALITY?" - The Fourteenth International Conference on the Unity of the Sciences Houston, Texas November 28 - December 1, 1985
"The "Null Hypothesis" for UFO reports, of which I am one of a handful of champions, states that no extraordinary stimuli are required to produce the entire array of public UFO perceptions in all their rich variety, wonderment, and terror. Known phenomena have produced all types of what is commonly known as "UFO reports", including apparitions of flying disks, radar and radio interference, terrifying chases and "intelligent maneuvers", telepathic messages, "missing time" and hypnogenic narratives, recollections of participation in military UFO retrievals, actual "secret documents", and so forth. There seem to be no types of reports which have not been, on record, produced at some point or another by prosaic stimuli and/or circumstances.
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Stupid UFOlogy Tricks
by Royston Paynter

In our discussions about UFOs and in browsing the web, IUFOS encounters, again and again, the same fallacious lines of reasoning being used to justify a belief that aliens are visiting the Earth. In this column I will discuss the errors in these arguments.
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Mainstream Scientists and Ufology
by Scott Allen Munro

Any individual UFO event may be investigated scientifically. If it can be proven a balloon, the hypothesis "The reported object was an alien spaceship" is falsified. But if the object is not identified, then it is unidentified. That's all. Not a lot of incentive in that to get a scientist involved. When a piece of alleged physical evidence is presented, it can be investigated scientifically. It has been pointed out that if the material came from another solar system, the elements in the material should contain different isotope ratios than those found on earth. But physical evidence is rarely produced, and none of it has ever been demonstrated to be extraterrestrial.  The reason scientists rarely devote themselves to UFO research is not merely the lack of evidence. It is the lack of scope for scientific research.
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Physical Evidence
IUFOS (Internet UFO Skeptics)

Skeptics are sometimes criticized for demanding physical evidence of alien visitations. It is an unreasonable demand, believers say, because aliens are intelligent and cunning, and one cannot expect them to leave physical evidence of their presence on Earth.  Well, such an argument may make sense to somebody who is prepared to believe in alien visitations as an act of faith, in the same way that some people believe in angels. But the undeniable fact of the matter is that there is no probative physical evidence that compels us to conclude that aliens are visiting the Earth.
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UFO's - The Skeptics Dictionary
by Robert Todd Carroll

A UFO is an unidentified flying object which has been identified as a possible or actual alien spacecraft. Such objects include meteors, disintegrating satellites, flocks of birds, aircraft, lights, weather balloons, and just about anything within the visible band of electromagnetism. So far, however, nothing has been positively identified as an alien spacecraft in a way required by common sense and science. That is, there has been no recurring identical UFO experience and there is no physical evidence in support of either a UFO flyby or landing.
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List of Things Mistaken for UFOs

Many people are surprised to learn that virtually 90% of all UFO reports can be and have been explained.  The major argument seems to be over whether the remaining 10% is "noise" or "signal".  Herewith, a list of things which have been the primary cause of UFO reports in the past.  It's a list that any investigator should be aware of when studying a particular report.  It was compiled by Donald Menzel, a noted debunker of the 50s and 60s, who characterized this list as "minimal and highly abbreviated".  (From "UFOs: A Scientific Debate", Sagan and Page, eds. consisting of papers presented at a symposium sponsored by the American Association for the Advancement of Science, held in Boston on Dec. 26-27, 1969, ISBN 0-393-00739-1) 
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Through the looking glass: The world of the UFO "believer"
Personal observations of Royston Paynter

Broadly speaking, there are two flavours of UFOlogy - a serious kind, practiced by means of the scientific method, and what I shall call "popular UFOlogy", the kind one finds on the bookshelves in the "New Age" section. There can be no doubt that UFOs really do exist - but "UFO" means "unidentified flying object", and as far as I am aware, there is no tangible proof that any UFO was an alien space ship. But it is undeniable that some people really do see (or think they see) things in the sky that they do not recognize. To call these things "UFO"s is perhaps prejudicial - because the words "flying object" imply a nuts-and-bolts apparatus such as an alien space ship. A better term would be "unidentified aerial apparition", the scientific study of which has led to the discovery of a number of unusual natural phenomena, such as "Earth lights", a kind of atmospheric discharge caused by geomagnetic activity.
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