In approaching the spacecraft hypothesis, the scientist asks first: What facts are we trying to account for? And second: Does the spacecraft theory account for these facts better than the normal explanations that are already available? After studying hundreds of UFO reports, however, he concludes that much of the startling “proof” that saucers are spacecraft is merely inference. Of the established facts, none requires a new theory to account for it; and no evidence exists that even faintly suggests, to the expert, that interplanetary visitors are involved. In the study of UFO phenomena this question of “evidence” is crucial. The careful investigator tries always to distinguish sharply between an observed fact, which is evidence, and an interpretation of that fact, which is not evidence no matter how reasonable it may seem. As a simple analogy, consider this situation: A man is sitting in his living room late at night; the rest of the family have gone to bed. Suddenly he is startled by a loud noise somewhere upstairs. Trying to account for the noise, he thinks of various possible causes--a burglar, the “settling” of the house, a mouse in the wall, someone dropping a shoe, the wind rattling a door, the sonic boom from a distant plane. If, without having further information, he decides that any one of these is the true cause, he is accepting a guess as though it were a fact. The real cause of the noise may be one of these or it may be something else that he hasn’t even thought of. Amateur investigators of UFOs publish many reports which they characterize as absolute proof that spaceships exist. The expert, analyzing the same reports, finds no proof at all because the actual facts and the interpretations of the witnesses are hopelessly confused. An early UFO case provides a typical example.