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Categorical Syllogism
A categorical syllogism is a type of argument with two premises—that is, a syllogism—and one conclusion. Each of these
three propositions is one of four forms of categorical proposition: A, E, I, and O.
In a categorical syllogism there are three terms, two in each premise, and two occurrences of each term in the entire
argument, for a total of six occurrences. The S and P which occur in its conclusion—the Subject and Predicate terms—
are also called the minor and majorterms, respectively. The major term occurs once in one of the premises, which is
therefore called the major premise. The minor term also occurs once in the other premise, which is for this reason
called the minorpremise. The third term occurs once in each premise, but not in the conclusion, and is called the
middle term.
The notion of distribution plays a role in some of the syllogistic fallacies: the terms in a categorical proposition are
said to be distributed or undistributed in that proposition, depending upon what type of proposition it is, and whether
the term is the subject or predicate term. Specifically, the subject term is distributed in the A and E type propositions,
and the predicate term is distributed in the E and O type propositions. The other terms are undistributed.
Finally, the A and I type propositions are called "affirmative" propositions, while the E and O type are "negative", for
reasons which should be obvious. Now, you should be equipped to understand the following types of syllogistic
fallacy.
Standard Form Categorical Syllogism
The word standard form categorical syllogism refers to the structure and arrangement of propositions in the
syllogism. A standard form categorical syllogism is arranged in this order:
Major Premise : All Muslims are devoted to Allah
Minor Premise : Muhammad is a Muslim
Conclusion : Therefore, Muhammad is devoted to Allah
Conclusion-indicators are words which imply that what about to follow is a conclusion. Therefore, so, ergo (Latin),
thus, hence, accordingly, consequently, in consequence, it implies that, shows that, it proves that, as a result, it means,
it follows that, we may infer that, for this reason, we may conclude, and othersare examples of conclusion-indicator.
Premise-indicatorson the other hand tell us that what about to follow is a premise. Since, because, as, inasmuch, but,
however, follows from, as shown by, as indicated by, and others are examples of premise-indicators.
Symbols in Syllogism
Terms Symbols Quality Symbols Quantity Symbols
Major Term P Affirmative + Universal u
Minor Term S Negative - Particular p
Middle Term M
To illustrate an argument using symbol, we have the following:
All poems are uplifting A : Mu + Pp
Some songs are poems I : Sp + Mp
Therefore, some songs are uplifting I : Mp + Sp
No abortionists are pro-life E :Pu + Mu
Some pro-life persons are Catholics I : Mp + Sp
Therefore, some Catholics are not abortionists I : Sp + Pp
Eight Syllogistic Rules
1. There must be only three terms in a syllogism
Example: All pitchers are containers
Jose in baseball is a pitcher
Jose in baseball is a water container

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All fathers have children
Pope Francis is a father
Pope Francis has children
Fallacy committed:Fallacy of Equivocation or Fallacy of Four Terms
2. Neither the major term nor the minor term may be distributed in the conclusion, if it is undistributed in the
premises.
Example: All Visayans are Malayans
No Tagalogs are Visayans
No Tagalogs are Visayans
No cats are dogs
All cats are animals
Therefore, no animals are dogs
Fallacy committed:Fallacy of Illicit Major or Fallacy of Illicit Minor
3. The middle term must not appear in the conclusion.
Example: All Pahiyas Festivals are colorful celebrations
All colorful celebrations are human expressions
So, all human expressions are colorful celebrations
No Filipinos are Indonesians
Some Asians are Indonesians
Therefore, some Indonesians are not Filipinos
Fallacy committed:Fallacy of Misplaced Middle Term
4. The middle term must be distributed at least once in the premises.
Example: All Bicolanos are Filipinos
All Boholanos are Filipinos
Therefore, All Boholanos are Bicolanos
All mammals are animals
Some animals are not bats
Therefore, some bats are not mammals
Fallacy committed:Fallacy of Undistributed Middle Term
5. Only an affirmative conclusion can be drawn from two affirmative premises.
Example: Every cat is sentient
Every cat is an animal
No cat is sentient
All Lycean students are humans
Pedro is a Lycean student
Therefore, Pedro is not human.
Fallacy committed:Fallacy of Negative Conclusion Drawn from Affirmative Premises
6. No conclusion can be drawn from two negative premises.
Example: No cheating is good
But corruption is good
No conclusion

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Some women are not pregnant
But some women are not doctors
No conclusion
Fallacy committed:Fallacy of Negative Premises
7. The conclusion follows the weaker premise.
Examples: All cellular phones are used in communication
But some cameras are cellular phones
Therefore, all cameras are used in communication
No jeans are shirt
But clothes are jeans
So, some clothes are jeans
Fallacy committed: Fallacy of Universal Conclusion Drawn From a Particular Premise, Fallacy of Affirmative
Conclusion Drawn From a Negative Premise
8. No conclusion can be drawn from two particular premises.
Example: Some animals are dugong
Some animals are butanding
No conclusion
Some philosophers are not mathematicians
But some mathematicians are not musicians
No conclusion
Fallacy committed:Fallacy of Particular Premises
INFORMAL FALLACIES
Formal fallacies are errors of reasoning by virtue of their forms. Informal fallacies are errors encountered in ordinary
discourse and, sometimes described as fallacies of language. Fallacies may be created unintentionally, or they may be
created intentionally in order to deceive other people. Sometimes the term “fallacy” is used even more broadly to
indicate any false belief or cause of a false belief.
Fallacies of Ambiguity (Unclear Meaning)
1. Fallacy of equivocation. Equivocation is the illegitimate switching of the meaning of a term during the reasoning.
This is also called fallacy of four terms.
Example: God is love, but love is blind, therefore, God is blind.
2. Fallacy of accent. The accent fallacy is a fallacy of ambiguity due to the different ways a word is emphasized or
accented.
Example: “Woman, without her, man is lost.”
3. Fallacy of amphiboly. This is an error due to taking a grammatically ambiguous phrase in two different ways
during the reasoning.
Example: Lost : The dog of a lady with a long tail.
4. Fallacy of composition. The composition fallacy occurs when someone mistakenly assumes that a characteristic
of some or all the individuals in a group is also a characteristic of the group itself, the group “composed” of
those members.

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Example: Jose is an intelligent boy
But Jose studies at Lyceum
Therefore, all who study at Lyceum are intelligent
5. Fallacy of division. Merely because a group as a whole has a characteristic, it often doesn’t follow that
individuals in the group have that characteristic. If you suppose that it does follow, when it doesn’t, you commit
the fallacy of division.
Example: The jigsaw puzzle when assembled is circular in shape. Therefore, each piece is circular in shape.
Fallacies of relevance (Irrelevant Premise or conclusion)
1. Argumentum ad baculum (appeal to force or the threat of force). If you suppose that terrorizing your opponent
is giving him a reason for believing that you are correct, then you are using a scare tactic and reasoning
fallaciously.
Example: You have to be good to us, or else you will fail the student’s evaluation.
2. Argumentum ad misericordiam (appeal to pity or emotions). You commit the fallacy of appeal to emotions when
someone’s appeal to you to accept their claim is accepted merely because the appeal arouses your feelings of
anger, fear, grief, love, outrage, pity, pride, sexuality, sympathy, relief, and so forth.
Example: You have to give me a passing mark, or else you’ll ruin my future.
3. Argumentum ad populum (appeal to the people). If you suggest too strongly that someone’s claim or argument
is correct simply because it’s what most everyone believes, then you’ve committed the fallacy of appeal to the
people. Similarly, if you suggest too strongly that someone’s claim or argument is mistaken simply because it’s
not what most everyone believes, then you’ve also committed the fallacy. Agreement with popular opinion is
not necessarily a reliable sign of truth, and deviation from popular opinion is not necessarily a reliable sign of
error, but if you assume it is and do so with enthusiasm, then you’re guilty of committing this fallacy.
Example: You should tune in to ABS-CBN, because it’s the most watched station this year.
4. Argumentum ad hominem (argument against the person). You commit this fallacy if you make an irrelevant
attack on the arguer and suggest that this attack undermines the argument itself.
Example: He should not be entrusted with the position, because he’s from a family of drug addicts.
Fallacies of Presumption (Premise Assumed)
1. Fallacy of Accident. This fallacy presumes that a general rule can apply to all situations without due regard to
their accidental features.
Example: The law states that you should not travel than 50 kph, thus, even if your father is dying, you
should not travel faster than 50 kph.
2. Fallacy of petitiopercipii. This means “begging the question.” A form of circular reasoning in which a conclusion
is derived from premises that presuppose the conclusion.
Example: Expert says that Joseph Estrada is the best president of the country,
Those experts are those who maintain that Joseph Estrada is the best president.
3. Fallacy of complex question. You commit this fallacy when you frame a question so that some controversial
presupposition is made by the wording of the question.
Example: “Have you stopped smoking marijuana?”
Fallacies of Indefinite Induction (Insufficient Samples)
1. Fallacy of false cause. Improperly concluding that one thing is a cause of another.
Example: He met an accident because he saw a black cat.

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2. Fallacy of converse accident. If we reason by paying too much attention to exceptions to the rule, and generalize
on the exceptions, we commit this fallacy. This fallacy is the converse of the accident fallacy. It is a kind of Hasty
Generalization, by generalizing too quickly from a peculiar case.
Example: Some foreigners are pedophiles, therefore, all foreigners are pedophiles
3. Argumentum ad verecundiam (appeal to inappropriate authority). This fallacy is committed when one cites an
authority in support of one’s argument but this authority is misplaced.
Example: Aswangsexist because our grandparents have always believed in their existence.
4. Argumentum ad ignoratiam (appeal to ignorance). This appears when one appeals to ignorance to win a case.
The fallacy of appeal to ignorance comes in two forms: (1) Not knowing that a certain statement is true is taken
to be a proof that it is false. (2) Not knowing that a statement is false is taken to be a proof that it is true. The
fallacy occurs in cases where absence of evidence is not good enough evidence of absence. The fallacy uses an
unjustified attempt to shift the burden of proof.
Example: Nobody has ever proved that God exists, therefore, God does not exist,
Dowden, Bradley. 2010. Fallacies.Available at http://www.iep.utm.edu/fallacy. Accessed last July 4, 2010
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Edition.Quezon City : C&E Publishing.
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orth/Thompson Learning.
Timbreza, Florentino T. 1992. Logic Made Simple. Quezon City : Phoenix Publishing House Inc.
Umali, Pepe SM. 2007. Logic: Art of Living with Reason.IntramurosManila :Mindshapers Co. Inc.