Common Fallacies in Thinking

Generalizing from a Particular,  or from too narrow a range of particulars, is a common error of induction.  We do not collect enough evidence, and we seem to assume that because we have evidence of X being repeated twice, X will always happen.  Because the one Eskimo in our circle of friends likes to read Anthony Trollope, we may generalize that Eskimos enjoy Trollope.  Clearly, such an assumption is illogical.  We need a greater sample; we need to spread the net wider for evidence.  If we cannot support a generalization, we must abandon it or admit its worthlessness as proof.

The Over-inclusive Premise.  In the furnace of argument, many logical errors are forged by means of the over-inclusive premise.  “All of us are guilty.”  “Everybody who goes to medical school is out for money.”  “All people who act like that are communists/fascists.”  These statements are generalizations (possibly from a limited sample).  If we say “some” instead of “all,” we are more sensible – and we have admitted that our charge is not overly inclusive.

Guilt by Association (or holiness by association, for that matter) is another common form of faulty thinking.  The Mafia, we believe, is an Italian organization.  So when we identify someone as Italian, the Mafia may cross our minds.  Everyone knows this sort of thing is absurd, yet if we do not keep constant scrutiny over ourselves, we fall into it again and again.  Politics thrives on guilt by association.  Because socialists believe in free medicine, anyone who believes in free medicine might be associated to be a socialist.  If we attach an emotional negative to the word socialist, we can think that we have just argued free medicine down.  We have just associated emotively; we have not argued at all.

Begging the Question.  In this error the arguer assumes the premise of an argument that the reader may question.  The arguer could try to prove the assumption, but fails to do so.  Someone might say, “The rising incidence of mongolism proves that early advocates of a test ban treaty were correct.”  The writer neither demonstrates that mongolism is rising, nor shows that nuclear testing causes mongolism.

Sequence as Cause, or post hoc ergo propter hoc, is a form of the nonsequitur (an inference or conclusion that does not follow from the premises or evidence).  The assumption is that if A follows B, B is the cause of A.  This assumption is not logical.  Again, the politics of paranoia adopts the arguments of sequence as cause.  Consider the following: “Rudolph Blast was in Newark the day before a bomb went off; therefore . . .” Such evidence is not even circumstantial, and it does not hold up in a court of law.  If a hurricane comes after a bomb test, we are not safe in assuming that the bomb test caused it.  Sequence is not causation and is inadequate evidence of it.

The Argument ad Hominem  (Latin for “at the man”) rises in us frequently when we lose our tempers.  The ad hominem argument diverts attention from issue to personality, and thus it is a refinement of evading the issue, and of the nonsequitur.  We ignore the issue and attack the person defending the issue or symbolizing it.

Analogy as Fact.  Analogies in argument are most useful.  They illustrate the sense in which we mean a statement that might otherwise be too tenuous to be understood.  They embody attitude and feeling, and they persuade by using exact carriers of feeling.  But we can fall into another common form of illogic in arguing from analogy as if it were fact.  Suppose we want to write about different civilizations that seem to have features in common – like beginning, developing, fulfillment, and decay.  To carry this idea to a reader, we invent an analogy; each civilization is like an organism: it is born, it grows up, it matures, it becomes old, and then it dies.  So far, so good.  We follow the abstract thought by associating it with concrete things.  But many writers become so accustomed to a dominant analogy that they begin to take it literally.  Arguing later that our own civilization must end, we say, “like all organisms, our society must come to death.”  The argument is invalid because a civilization is not literally an organism; therefore, we have not proved that what is true of an organism will be true of civilization.  The analogy is not the thing itself.