There are common ways of thinking that might initially seem all right, but which in fact do not provide adequate support, either inductive or deductive, for the stated conclusion,

1) The Delphi Fallacy: The Fallacy of Vague Prediction

In ancience times, the oracle at Delphi was noted for her ability to see the future.  A Greek king sent off to see what his fortunes in a coming war would be, and the oracle told him that if he went to war, "a great kingdon would founder."  Encouraged, the king did start his war -- and it was his own kingdom that foundered.  Did the oracle's successful prediction provide justification for the belief that she could predict the future?  No -- if a prediction is sufficiently vague, it stands a good chance of bveing fulfilled, no matter what it is.  Too, note that there is no theoretical model here involved in the reasoning -- a major difference between scientific and pre-scientific thinking.

2) The Jeane Dixon Fallacy: The Fallacy of Multiple Prediction

At the beginning of the year, the tabloids are loaded with the predictions of contemporary psychics.  Jeane Dixon was one of the most famous of these "public psychics."  She used to issue whole sets of predictions on a regular basis.  These were often vague, but not so vague as to assure her of success.  The fallacy here is looking at only part of the evidence and being mislead by the isolated successful prediction into believing that there has been a good test of the case, i.e., that Jeane Dixon is able to see the future.  Too, I have shown you in class that Mrs. Dixon never made a correct prediction in print, from her prediction (in 1968) that Russians would be the first to the moon, to her predicting that a giant asteroid would hit the earth in the mid-1980s and that Princess Diana's first child would be a girl.  Not a great track record.

3) The Patchwork Quilt Fallacy: No Prediction at All

In the Patchwork Quilt Fallacy, a hypothesis is pieced together in such a way that it logically implies the already known facts. One has the illusion that the hypothesis predicts the facts, but this is, indeed, only an illusion.  No new discoveries are predicted by the hypothesis at all, and none of the facts count as evidence for the hypothesis -- they are merely logically compatible with it.  Conspiracy theories are usually examples of Patchwork Quilt Fallacy, and also hypotheses like the ancient astronauts theory of human cultural origins found in Erich Von Danikin's infamous book,  The Chariots of the Gods.

4) Ad Hoc Rescue: Failed Prediction

A religious cult predicts that UFOs will land at a specific time and place and bring us a message of hope and peace.  The media, however, learn of this prediction and it hits the news.  On the day appointed, newspeople and the public, as well as members of the cult, are all awaiting the arrival of the aliens.  When the space folk don't show, the cult members announce that they been scared off by all the commotion, but will arrive at a currently unspecified date in the future.  What the cult members have done here is to affirm the consequent -- that it, whatever happens, they simply incorporate it into their original theory.  When you affirm the consequent, nothing can ever disprove the original assertion -- in this case, that aliens exist.  But if nothing can disprove the claim, there is also no particularly compelling reason to believe it, too.  Religious millenarianism often uses Ad Hoc Rescue, as does Jeane Dixon.

5) Justification by Elimination: Deductive Prediction

Suppose you have three hypotheses (say, H1, H2 and H3) and it is given that one of the three is true.  If you then determine that H2 and H3 are false, it follows that H1 is true -- right?  Well, no.  The conclusion is deductively valid, but it cannot be said to be true unless you focus on H1 from the start and ask whether it might not also be false. Arguments subject to this fallacy can be elaborate and hard to spot, but a simple example is that of a person spotting an object in the sky, deciding it is not a plane or the planet Venus, and then shouting out, "Look, a UFO!"  Hey, it might also be a weather balloon, an experimental US aircraft powered by zero-point energy, or even Superman.  You don't know until you look and H1.