Kinds of Syllogisms 1. Categorical Syllogism -
is composed composed of Categorical propositions
-
consist of 2 premises and conclusion
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contains 3 terms : Major, Minor, and Middle term Ex. All inventors are scientist Some inventors are well-known worldwide Hence, some people who are well-known worldwide are scientist
2. Hypothetical Syllogism -
is composed of Hypothetical propositions propositions
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the terms are not identified as Major, Minor, and Middle Ex. If the suspect is found guilty he will serve time in prison But he will not serve time in prison Ergo, he was not found guilty
Categorical Syllogism The General Laws Governing Categorical Syllogism
1. Dictum de Omni -
Whatever is + u, in a formal formal manner, manner, should also be + of its logical parts Ex. If “all X are Y”, and “some Z are X” then “some Z are Y”
2. Dictum de Nullo -
Whatever is - u, in a formal manner, should should also also be - of its logical parts Ex. If “all X are not Y”, Y”, and “some Z are X” then “some Z are not Y” rd
3. If each of 2 concepts agrees w/ the same 3 concept, then they also agrees w/ each other -
If A agrees w/ C & B agrees w/ A, then B & C agrees w/ each other. A=C B=A B=C rd
4. If one concept agrees w/a 3 term and other disagrees w/ the same term, then they disagrees w/ each other -
If A agrees w/ B, but C don’t agree w/ A, then B & C don’t agree w/ each other. A=B CA BC rd
5. If each of 2 concepts disagrees w/ the same 3 concept, then there’s no conclusion. - If A disagrees w/ B & C disagrees w/ A, then nothing follows. AB CA No conclusion
8 Laws of Categorical Syllogism
Rule # 1 Only 3 terms in the syllogism
Fallacy of 4-term construction
Fallacy of Equivocation – Equivocation – 1 term express 2 diff. meaning
Rule # 2 No term may have a greater extension in the conclusion than the premise
Fallacy of Illicit Major Term – Term – when major term is p and conclusion is
u
Fallacy of Illicit Minor Term – Term – when minor term is p and conclusion is
u
Rule # 3 The middle term must not appear in t he conclusion.
Misplaced Middle Term – Term –when when middle term appears in the conclusion
Rule # 4 The middle term must be taken as u in the premise at least once.
Undistributed Middle Term - when middle term is taken twice as p
Rule #5 If both premises are +, the conclusion must be +
Fallacy of a negative conclusion
Rule # 6 No conclusion can be drawn from 2 negative premises.
Fallacy of 2 negative premises
Rule # 7 No valid conclusion can be derived from 2 p premises.
Fallacy of Double Particular Premises
Rule # 8 The conclusion always follows the weaker side.
Fallacy of a Stronger Conclusion than the Premises.
Hypothetical Syllogism
1. Conditional Syllogism - composed of: Condition Proposition – Proposition – Major Premise Categorical Proposition – Proposition – Minor Premise and Conclusion
Ex.
If it rains, then the ground is wet
p
q
It Rained
p
Ergo, the ground is wet
q
Laws of Condition 1. If p is accepted, then q must be accepted R
