informal fallacies

definition of fallacy

It’s a mistake committed in reasoning. i.e a fallacy is an argument which appears to be valid but in reality it is not.


  • It help us to detect common errors in reasoning
  • It enables us to avoid incorrect reasoning
  • The study of fallacies enables us to know them, avoid them, correct them ever necessary


There are basically 2 types of fallacies. Namely: formal and informal fallacies.


These are fallacies committed when one violates one or more of the deductive arguments. These rules include fallacy of definition and general rules of syllogism. Therefore informal fallacies deals with mistake in the structure or form of the argument eg

All human beings are mammals

Some rational beings are noise beings

Therefore some rational beings are mammals

This argument has committed the fallacy of Quoternerio terminorium


These are fallacies committed due to logical mistakes in our everyday discourse.

There are two types of informal fallacies namely: fallacy of ambiguity and fallacy of relevance

  1. Fallacy of relevance

This fallacy is committed when the premises are not relevant enough to establish the truth of the conclusion of that argument i.e. the premises of such arguments are incapable of providing the truth of the conclusion that is why Aristotle called it the fallacy of diotenem. The fallacy of relevance include the following

  • Argumentum Ad Hominem: it is a fallacy committed when someone directs his arguments against a person rather than against what the person says g. one might argue that the sermon preached by the pastor David against adultery shouldn’t be taken into consideration because he commits adultery as well.
  • Argumentum populum (appeal to the crowd or mass): it is a fallacy committed when one arouses the feeling of the crowd in order to win support to a conclusion which cannot be accepted by a valid argument g. one may accept that since millions of Christians are running to the synagogue church of ST David, Leila too should go
  • Argumentum Ad Misericordian (appealing to pity): this fallacy is committed when one appeals to the feeling of pity to get a conclusion accepted. g. the teacher wants to beat Jessie but she appeals on the basis that her hand will become red.
  • Argumentum Ad Baculum (appeal to force): this fallacy is committed when someone uses force in order to make a conclusion accepted especially when rational arguments have failed g. you know that I am aware of how much you have embezzled in the PTA funds so you better have elected in the new bureau or the public get to know about it.
  • Argumentum Ad Ignorantium (Appeal to ignorance): it is committed when someone argues that a conclusion should be accepted simply because it has not been proven false or that it is false because it has not been proven false g. Jordan argues that the cos of 60 is not 0.5 because it has not been proven as such
  • Argumentum Ad Verecuriam (appeal to authority): this is a fallacy committed when one appeals to an unreliable authority and assumes without sufficient reason the authority is reliable g. one may argue that the use of contraceptive is bad because the pastor said so. This is a fallacy because the pastor is not a member of the medical filed.
  • Fallacy of ignoroi-Elenchi: this is committed when an argument supposed to establish a particular conclusion is rather denoted to prove different one g. In attempting to prove that an accused student of fraud, the prosecution may argue that fraud is bad because it leads to social injustice
  • The fallacy of accident: it is committed when someone applies general rules to particular cases whose exceptional circumstances may render the rule Inapplicable g. there may a rule that all athletes preparing for particular competition must do intensive jogging but to apply this general rule to an athlete suffering from acute health problem render this rule inapplicable
  • The fallacy of petition principii: its committed when argues in circle (arguing round saying the same thing in different ways. g. The match of yesterday was marvellous, the match of yesterday was fantastic, in fact it was it excellent.
  • The fallacy of Tuquoque: It is committed when one justifies his or her action on the basis that someone else is also doing the same thing. She justify that she is a prostitutes because her mother is also doing it.
  • The fallacy of sequitur: it is committed when the conclusion of an argument does not follow from the premisesg.

All Cameroonians are intelligent

Shekinah is a Cameroonian

Therefore James is a tall boy

  • Fallacy of False Cause: there are two types of this fallacy
  1. Non causa pro Causa: it is committed when wrong cause is attributed to an event g. Schneider passed his exams because he was playing everyday
  2. Post Hoc Ergo Propter Hoc: the Latin word means that “after, therefore because of this”. This is committed when someone believes that since an event comes before another, then the first is the cause of the event g. Since the construction of the gate has reduced the lateness in our school, therefore,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
  • Fallacy of complex question: this is committed when a double questions is asked in such a manner that one question is implied in the other g. the discipline master asked toMohammad whether he still steals pens, if he says yes, he will be punished for stealing pens, if he says no, it implies he was previously stealing pens.
  • Fallacy of hasty generalisation: this is a fallacy committed when someone considers only exceptional cases and hastily generalises them to a rule that fit them aloneg. Romarick usually eats banana and he is intelligent, therefore banana gives intelligence.



These are fallacies committed when the arguments are flawed because they contain a double meaning or there is confusion between two closely linked concepts. As such, Aristotle called these fallacies IN DICTIONE because they are errors which result from diction.

The types of fallacies of ambiguity are;

  • Fallacy of Equivocation: this fallacy is committed when a given key word or phrase is used in two or more different ways in the same context g.

Partisans are not to be trusted

Democrats are partisans

Therefore democrats are not to be tested

  • Fallacy of Amphibody: this fallacy is committed when there is ambiguity or double meaning in an argument, due to a syntactic difficulty such as a grammatical error or a mistake in punctuation e.g. “Miranda  loves Glory because it is her sister” have many interpretations and is therefore amphibious because it could mean Miranda loves glory because glory is her sister or vice versa
  • The Fallacy of accent: this is a fallacy committed when a given statement is a subject to several different meanings, depending on which word or phrase in the sentence is stressed. A person who quotes another and omits the inverted comma commits the fallacy of accent e.g. “Socrates said man know thy self”. The punctuation mark in the sentence is left out making it to look like an ordinary sentence and not in the reported speech and consequently can be interpreted in different ways adequately punctuated.
  • Fallacy of composition: this is reasoning fallaciously from the properties of the parts of a whole to the properties of the whole its self-e.g. it can be stated since Ryan, Jonathan, Blessing are students from GBHS Nkol Eton Yaoundé are very intelligent, therefore all the students from that school are also intelligent.
  • The fallacy of Division: this is fallacy committed when someone argues that what is true of whole must also be true of its parts e.g. when someone argues that since Cameroon is poor then all Cameroonians are poor, the fallacy of division is committed



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