Would eating a soup of ground up tiger penis costing $400 per bowl make you sexually potent? How about popcorn? Or if this fails to improve your life why not get ready to be "raptured" when Jesus comes? If Jesus delays will a UFO pick you up instead?

How can we distinguish sensible claims from nonsensible ones? The absurd from the non-absurd? When should we show interest with an open mind and when should we decide we're wasting our time and close our mind?

These are important questions – considering how many people have killed or hurt each other over conflicting beliefs. Correct beliefs will also help in making right decisions over how to use our resources of time, wealth and energy. If for example you believe the "rapture" of the saints is at hand you might give all your time, wealth and energy to the sect making such a claim and end up disillusioned!

Francis Bacon (1561-1626) was one of the fathers of modern science yet suspected that wounds could be treated by applying ointment to the weapons that caused them.

Isaac Newton (1642-1727) invented calculus and made many discoveries in physics. Yet he also believed that the l1th horn of the 4th beast (in the Bible book of Daniel) meant the Church of Rome and which would be destroyed between 2035 and 2054 AD.

In another interpretation of Daniel, Newton predicted that people would travel at 50 miles per hour. The French writer/philosopher Voltaire (1694-1778) responded:

Howard Atwood Kelly (1858-1943) was a founder of gynaecology and a surgeon who pioneered cocaine anaesthesia. Yet he was a Christian who believed the story of Jonah and the whale. American journalist and linguist Henry Louis Mencken (1880-1956) wrote when reviewing a book by Kelly:

Famous anthropologist Margaret Mead (1901-1978) believed in visits by flying saucers.

Religion often warps peoples' judgement. In 1992 about 20,000 members of Mission for the Coming Days were caught in a doomsday craze and predicted their ascent into the sky for October 29, 1am, Sydney time. Also there are thousands of scientists who believe the Universe is less than 10,000 years old – that it popped into existence at God's command. When asked about our ability to see distant galaxies when the light takes millions of years to reach Earth such scientists might cite Barry Setterfield who thinks (contrary to science) that the speed of light used to be much faster!'

Obviously, then, it is easy to have wrong beliefs even absurd beliefs. Sir Arthur Conan Doyle (1859-1930) physician and writer of detective stories, believed in fairies!

Is there a reliable way of distinguishing absurd beliefs from correct beliefs?

Let me say straight away that there is no foolproof, simple, method. If there were then almost all disagreement about religion, the supernatural, science and the paranormal could be ended by applying our foolproof rule or procedure!

Nowadays ideas about "chaos" and "superstring theory" and multiple dimensions suggest that the Universe is not a predetermined "clock-work universe" but that the future really is open, often unpredictable.

All this does NOT mean that attempts to choose correctly between contradictory beliefs are hopeless.

I'll now present a few guidelines which will assist such attempts.

The editorial of INVESTIGATOR No. 1 said: "If something can't be demonstrated experimentally, or at least inferred inductively, then the rational person won't treat it as an established truth. The onus is on any person who denies that the world is as scientific instruments reveal it."

This INVESTIGATOR comment is still useful. If an experiment plus the results which will support the hypothesis are carefully described so that others can verify everything by repeating it then the results can be provisionally accepted.

I say "provisionally" in order to allow for fraud or some confounding factor initially overlooked by everyone. If the observation/experiment is often duplicated, and the hypothesis continues unfalsified, then we'll have to regard it as a "fact".

A useful test when someone makes a claim is to ask: "Does it conform with what science has shown to be the case?" An alleged perpetual motion machine will be contrary to thermodynamics. A claim to levitation will be contrary to laws of gravity and motion.

If someone reports a miracle, say levitation, we might remember a principle of Scottish philosopher David Hume (1711-1776): "No testimony is sufficient to establish a miracle unless the testimony be of such that its falsehood would be even more miraculous than the fact which it endeavours to establish."

In practice it would be hard to apply Hume's principle since we lack clear measures of the "miraculousness" of various hypothetical events.

Another principle often remembered is Ockham's Razor. William of Ockham (1285-1349) was a philosopher and theologian. His "razor" was that "entities are not to be multiplied beyond necessity." Similar to this I would suggest choosing the simplest explanation which conforms with observation.

Long ago the simplest explanation for the rising and setting of the sun was that the sun moves around the Earth. Eventually as more observations were made and facts discovered, this "simple" explanation had to be supported with more and more assumptions so that what at first was simple became increasingly complicated. The new simple explanation eventually was that the observed rising and setting is due to the rotation of planet Earth!

Another procedure to evaluate beliefs and claims is to consider predictions and inferences which follow from them. If an inference is fulfilled it supports the original claim that gave rise to the prediction. Believers in biological evolution sometimes describe hypothetical ancestors of species which existed later. If fossils of such hypothetical ancestors are later discovered then the theory of Evolution has gained in credibility.

Many beliefs are inferred by using inductive logic. This involves inferring/predicting/generalizing from a set of previous observations. If you find you score 50% (approximately) heads when tossing a coin 1,000 times you would predict an approximate 50% score on future sets of 1,000 tosses.

Often there are rival predictions based on rival sets of data. There is one writer for INVESTIGATOR who likes to show us Bible points which skeptics thought were wrong but which were correct after all. Based on such accuracies he would probably tell us that the story of Jonah is (also) literally true. Another person might in contrast point to a zero survival rate of people eaten i.e. completely eaten by sharks and make an opposite prediction.

In the book Philosophical Problems and Arguments (1982) we read: "An inductive argument from evidence to hypothesis is inductively cogent if and only if the hypothesis is that hypothesis which, of all the competing hypotheses, has the greatest probability of being true on the basis of evidence."

In many situations this rule will help us choose the best, most likely to be right, conclusion.

Often, however, we simply won't know "which … competing hypothesis has the greatest probability" because a probability calculation will be lacking.

What do we do if after we've tried to apply the rules and methods I've discussed and we still can't tell whether a claim is true or false? Usually it would make sense to either remain skeptical or at least to suspend judgement until we get further evidence. In other words keep on investigating. This way your mind stays open.