Syllogistic Rules And Fallacies.

Below are the syllogistic Rules And Fallacies in categorical proposition.


1. Avoid four terms.

2. Distribute the middle term in at least one premise.

3. Any term distributed in the conclusion must be distributed in the premises.

4. Avoid two negative premises.

5. If either premise is negative, the conclusion must be negative.

6. No particular conclusion may be drawn from two universal premises.

Associated Fallacies

1. Violated four terms a standard proposition must have (major, minor and middle term).

2. Undistributed middle

3. Illicit process of major (illicit major); illicit process of minor (illicit minor).

4. Exclusive premises

5. Drawing an affirmative conclusion from a negative premises.

6. Existential fallacy.

Example of these rule mention above with their categorical syllogism.

Rule 1.

Noted. Words with italic are middle terms.

All dogs are animals

No dogs are mammals

Therefore No animals are humans.

from here it violent the rule of four terms fallacy. In categorical syllogism it’s of three terms which are major, minor and the midday. From the above example, its more than three terms.

Rather it supposed to be

All dogs are animals

No dogs mammals

Therefore, No mammals(major term) are animals (minor term).

2. Rule 2.

Middle term must be distributed atleast on of the premises.

No birds are mammals 

All bats are mammals

No bats are birds.

From the illustration above, the first premise mammals is distributed where as the second premise- mammals is undistributed.

Rule 3.

No birds are mammals 

All bats are mammals

No bats are birds.

From here, the major term- bat are distributed in conclusion likewise minor term- birds are also distributed in the conclusion.

Rule 4. There should not be two negative premises.

No Namibians are Libyans

Some Namibians are not Nigerians.

Some Nigerians are not Libyans.

From here, its invalid because of the two negative premises.

Rule 5.

Of either of the premises is negative, the concrete should be negative also.

No saints are immoral persons

All saints are psychologically distributed.

Therefore, No immoral persons are psychologically distributed.

From here the first premises is negative where as the the conclusion is negative. Hence it’s absolutely valid.

Rule 6.

Two particular premises no universal conclusion.

Some moroccons are Spanish speakers

Some Nigerians are not moroccons 

All Nigerians are Spanish speakers.

From here its absolutely invalid because it’s existential fallacy.

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