Fallacies in Logic are errors in reasoning. A fallacy occurs when the premises of a given argument do not support the conclusion they are purported to support. In any argument, there is a claim the truth of any given premises if granted support the conclusion either necessarily in the case of deductive arguments or by some probability in the case of inductive arguments.
However, in most cases, upon closer examination and analysis of most arguments, it is found that the claim is not justifiable. In such cases, the claim of the premises does not support the claim of the conclusion, or weakly support the conclusion. When such happens, it is said that the arguments have committed fallacies in logic.
Formal Fallacies in Logic are reasoning that deviate from the established correct forms of reasoning. Any reasoning that does not conform to the established structure or form of correct reasoning definitely commits a formal fallacy. Therefore, to detect a formal fallacy simply requires an examination of any given argument against the many correct forms.
Informal Fallacies in Logic emanate from inconsistency in meanings within an argument. When the meaning of the premises collectively does not justify the conclusion then a formal fallacy is committed. Informal fallacies in logic can be categorized into three groups: fallacies of relevance, fallacies of presumption and fallacies of ambiguity.
Fallacies in Logic: Fallacies of Relevance
These Fallacies in Logic may perhaps be better referred to as fallacies of irrelevance since in them the conclusions are based on premises which are irrelevant to their claims.
- Argument from ignorance – Argumentum ad Ignorantiam
These Fallacies in Logic occur whenever a conclusion or a view is claimed to be true or correct simply because its contrary has not been proved. E.g. the failure of logicians to prove that God exists does not necessarily meaning God doesn’t exist.
- Appeal to people – Argumentum ad populum
These Fallacies in Logic occur whenever an argument plays upon people’s needs by exciting their emotions and enthusiasm in order to have its conclusion accepted. This fallacy is many a times committed by leaders/politicians.
- Appeal to force – Argumentum ad Baculum
These Fallacies in Logic occur when physical or psychological threat, be it direct or veiled, is used against somebody in order to force or coerce one into agreeing to one’s conclusion, suggestion or view.
- Appeal to pity – Argumentum ad Misericordiam
These Fallacies in Logic are committed when one evokes pity or emotion from listeners, readers or audience by appealing to his/her pitiable or miserable condition in order for the listener, reader or audience to accept his/her claim.
- Appeal to inappropriate authority – Argumentum ad Verecundiam
On a balance, we tend to easily go with the opinion of experts in their areas yet that in itself is not a guarantee that their opinions are correct. However, these fallacies are committed when appeal is made to an illegitimate or inappropriate authority in order to have a conclusion or view accepted.
- The fallacy of slippery slope.
These Fallacies in Logic occur when an arguer presents a conclusion based on an unlikely chain reaction. E.g. ‘Immediate steps should be taken to curb pornography. The continued manufacture and sale of these materials will lead to an increase in sex related crimes such as rape and incest. This will gradually erode the moral fabric of society and in turn an increase of crimes of all sorts.’ It is not certain that these things will happen. (More from Dr. Oriare Nyarwath’s book ‘Traditional Logic: An introduction’)
Fallacies in Logic: Presumption
These Fallacies in Logic are committed when the premises presume the very conclusions they are supposed to prove or justify. In some cases, the arguments presume or conceal some premises.
- The fallacy of begging the question – Petition Principii
Petition principii in Fallacies in Logic simply means postulation of the beginning. In this context to postulate means to use as true a premise whose truth is contentious as basis for a conclusion. So, in essence, every form of the fallacy of begging the question is a circular argument. To beg the question is to assume the truth of what one is to prove in the effort to prove it and this kind of reasoning still leaves the question unanswered.
- The fallacy of false dichotomy
These fallacies are also known as the fallacy of dilemma or bifurcation. These fallacies in logic emanate from the mistaken disjunction of the ‘either…..or…’ formulation of a premise being mistaken in the sense that it is used to present only two alternatives in a situation where there is a possibility of more than two possibilities. (More from Dr. Oriare Nyarwath’s book ‘Traditional Logic: An introduction’).
Fallacies in Logic: Fallacies of Ambiguity
These Fallacies in Logic are committed when ambiguous terms or phrases are used and in the end are rendered defective and thus fallacious.
- Fallacy of equivocation
These Fallacies in Logic are committed when a term which has more than one meaning is used in such a way that it is not clear which of the possible meanings is intended.
- Fallacy of amphiboly
Amphiboly can simply mean an ambiguity of a phrase or expression. This comes about due to improper grammatical construction which therefore makes its meaning indeterminate and thus an amphibolous proposition. These Fallacies in Logic will therefore occur when an amphibolous proposition is used in an argument.
- Fallacy of composition
These Fallacies in Logic occur when there is an illegitimate transference of attributes of parts or members of a whole pr collectivity. E.g. ‘sodium and chlorine are highly poisonous. Therefore, sodium chloride (table salt) is highly poisonous.’ The conclusion is not true.
- Fallacy of division
These are the opposite of the fallacies of composition. E.g. ‘sodium chloride (table salt) is not poisonous. Therefore, sodium and chlorine are not poisonous.’
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Conclusion on Fallacies in Logic
These are the Fallacies in Logic that should be avoided for any form of reasoning to be said to be right.