Let’s examine the process of critical evaluation by thinking through a sample belief: “I believe that aliens have visited the earth in some form.” A Gallup Poll found that 42 percent of American college graduates believe that flying saucers have visited the earth in some form.Many reputable people have seen UFOs and had personal encounters with aliens. The government has documented these in secret files, which include the UFO crash at Roswell, New Mexico, in 1947. Government attempts at concealment and cover-up have been transparent.Although many individuals have testified about alien encounters over the years, almost all scientific authorities have been extremely skeptical. They emphasize that all of the “evidence” is unsubstantiated, controversial, indirect, and murky—the markings of pseudoscientific fantasies. If aliens and UFOs exist, why haven’t they announced their presence in an incontrovertible fashion? Some of the most intriguing evidence comes in the form of the government’s belated and somewhat bizarre explanations for UFO sightings and the alleged Roswell incident. On June 25, 1997, the Air Force announced that the mysterious happenings in the New Mexico desert in the late 1940s and 1950s were in fact experiments involving crash dummies and weather balloons. Six weeks later, on August 3, 1997, the CIA “admitted” that the U.S. government had lied about alleged UFO sightings in the 1950s and 1960s to protect classified information regarding top-secret spy planes, the U-2 and SR-71. Why did the government suddenly attempt to explain these mysteries after all these years? And why does there appear to be contradictory testimony from different parts of the government? Why do the government explanations seem almost as fanciful and farfetched as the UFO stories?There are many books supporting alien visitations and alien abductions.Although many books regarding UFOs have been written, few have been more than unsubstantiated speculation. Philip J. Corso, who served on the National Security Council under President Dwight D. Eisenhower, contended in his book  (Pocket Books, 1997) that he personally directed an army project that transferred to the military various types of technology recovered from the alien ship that crashed in the desert. To date, efforts to prove or disprove his account have been inconclusive. After reviewing written accounts and interviewing people claiming to be alien abductees, Dr. John Mack, a psychiatry professor at Harvard Medical School, came to the conclusion that many of these reports are true. Though he was harshly criticized by his colleagues, Dr. Mack became instantly popular on the UFO circuit, and he convened a conference at which 200 mental health professionals gathered to discuss alien abductions.There are many photographs of UFOs and eyewitness accounts from people who have seen alien spacecraft. There have also been accounts of alien abductions. In addition, the movie  purportedly shows an alien being dissected.There have been innumerable UFO sightings, many of which can be explained by the presence of aircraft in the vicinity, meteors, or some other physical event. However, there is a core of sightings, sometimes by large groups of reputable people, that have not been satisfactorily explained. There are a number of photographs of “flying saucers” taken at a considerable distance, and though provocative in their possibilities, they are inconclusive. Most reports of alien abductions have been considered by the scientific establishment to be hoaxes or the result of mental illness or hallucinations—at least until Dr. Mack’s analysis noted previously. Medical experts and moviemakers have derided  as a crude hoax, although a small number of people knowledgeable about physiology and moviemaking techniques find it persuasive. There is no documented history of where the film came from, a fact that undermines its credibility.I have personally spoken to several people who are convinced that they saw things in the sky that looked like flying saucers. The perceptions of eyewitnesses are notoriously unreliable. People consistently mistake and misinterpret what they experience and often see what they want to see. In evaluating the testimony of personal experience, we must establish independent confirmation.