The Art of Logical Thinking Part 9

_Fallacies of Observation_ result from incorrect methods of observation among which may be mentioned the following: (1) _Careless Observation_, or inexact perception and conception; (2) _Partial Observation_, in which one observes only a part of the thing or fact, omitting the remainder, and thus forming an incomplete and imperfect concept of the thing or fact; (3) _Neglect of Exceptions and Contradictory Facts_, in which the exceptions and contradictory facts are ignored, thereby giving undue importance to the observed facts; (4) _a.s.sumption of Facts_ which are not real facts, or the a.s.sumption of the truth of things which are untrue; (5) _Confusing of Inferences with Facts_, which is most unwarrantable.

_Fallacies of Mistaken Cause_ result from the a.s.sumption of a thing as a cause, when it is not so, of which the following are familiar examples: _Subst.i.tuting the Antecedent for the Cause_, which consists in a.s.suming a mere antecedent thing for a _cause_ of another thing. Thus one might a.s.sume that the crowing of the c.o.c.k was the _cause_ of daybreak, because it _preceded_ it; or that a comet was the cause of the plague which followed its appearance; or in the actual case in which a child reasoned that doctors _caused_ deaths, because observation had shown that they always visited persons before they died; or that crops failed because a President of a certain political party had been inaugurated a few months before. Some fallacies of everyday reasoning are quite as illogical as those just mentioned. _Subst.i.tuting the Symptom for the Cause_, which consists in a.s.suming as a _cause_ some mere symptom, sign or incident of the real cause. To a.s.sume that the pimples of measles were the _cause_ of the disease, would be to commit a fallacy of this kind. We have mentioned elsewhere the fallacy which would a.s.sume silk-hats to be the cause of Civilization, instead of being a mere incident of the latter.

Politicians are fond of a.s.suming certain incidents or signs of a period, as being the _causes_ of the prosperity, culture and advancement of the period, or the reverse. One might argue, with equal force, that automobiles were the causes of national prosperity, pointing to the fact that the more automobiles to be seen the better the times. Or, that straw hats produced hot weather, for similar reasons.

_The Fallacy of a.n.a.logy_ consists in a.s.suming a resemblance or ident.i.ty, where none exists. We have spoken of this in another chapter. Brooks says, also: "It is a fallacy to carry an a.n.a.logy too far; as to infer from the parable of the praying of the importunate woman that G.o.d resembles the unjust judge."

In conclusion, we would call your attention to the following words from Jevons, in which he expresses the gist of the matter: "It is impossible too often to remind people that, on the one hand, _all correct reasoning consists in subst.i.tuting like things for like things_, and inferring that what is true of one will be true of all which are similar to it in the points of resemblance concerned in the matter. On the other hand, _all incorrect reasoning consists in putting one thing for another where there is not the requisite likeness_. It is the purpose of the rules of deductive and inductive logic to enable us to judge as far as possible when we are thus rightly or wrongly reasoning from some things to others."