By 

Dagoy, Arlyn A.Curameng, Sheryl S.Dela Cruz, Kim C.Calso, Geli May N.

HYPOTHETICAL SYLLOGISM

Hypothetical syllogism is one whose major premise is a hypothetical proposition while its minor premise and conclusion are categorical propositions.

 

Hypothetical Proposition Conditional statement If, then Does not affirm nor negate the components only the

nature and validity of their connection

Categorical Proposition All S is P No S is P Some S is P Some S is not P S is the proposition is all about, the P affirms or denies

Three kinds of Hypothetical Syllogism

1. Conditional Syllogism

2. Disjunctive Syllogism

3. Conjunctive Syllogism

Conditional Syllogism

  CONDITIONAL SYLLOGISM is one whose

major premise is a conditional proposition consisting of an antecedent and consequent, while the minor premise affirms or denies either the antecedent or the consequent of the major premise and the conclusion merely expresses’ whatever follows from its affirmation or denial.

 Rules:Posit the antecedent, posit the consequentSublate the consequent, sublate the antecedentPosit the consequent, no conclusionSublate the antecedent, no conclusion

Posit the antecedent, posit the consequent

 In symbolic logic, this is known as MODUS PONENS. If the antecedent is affirmed in the minor premise, the consequent must also be affirmed in the conclusion. The truth of the consequent follows from the truth of the antecedent.

Example: If someone wins in the million-peso lotto draws, he becomes a millionaire. But, Nikki wins the million-peso lotto draw; Nikki becomes a millionaire.

  

Sublate the consequent, sublate the antecedent

 In symbolic logic, this is known as MODUS TOLLENS. If the consequent is rejected in the minor premise, the antecedent must also be rejected in the conclusion. The falsity of the antecedent follows from the falsity of the consequent.

 

Example: If someone wins in the million-peso lotto draws, he becomes a millionaire. But, Nikki does not become a millionaire; Nikki does not win in the million-peso lotto draw.

 

Posit the consequent, no conclusion  This rule gives rise to the fallacy of affirming the consequent

which is committed when the consequent is affirmed in the minor premise.

 Example: If someone wins in the million-peso lotto draws, he

becomes a millionaire. But, Nikki becomes a millionaire; Nikki wins in the million-

peso lotto draw.  Sublate the antecedent, no conclusion  This gives rise to the fallacy of rejecting the antecedent which is

committed when the antecedent is rejected in the minor premise. Example: If someone wins in the million-peso lotto draws, he

becomes a millionaire. But, Nikki didn’t win in the million-peso lotto draw;

Nikki didn’t win become a millionaire.   

Different Patterns of the Conditional Syllogism A = antecedent B = consequentThe relation that exists between the two is expressed by the sign: (colon).

Exception: 

There are few cases in which one can conclude with certainty (a) from the truth of the consequent to the truth of the antecedent, and (b) from the falsity of the antecedent to the falsity of the consequent. But this is due not to the legitimate nature of the conditional inferential procedure employed but to the formal necessity involved in the matter in the conditional major premise.

 Example: If this month is December, next month is

January; But this month is not December; Next month is not January

DisjunctiveSyllogism

DISJUNCTIVE SYLLOGISMIt is one whose major premise is a disjunctive

proposition consisting of alternatives (disjuncts), while the minor premise affirms or denies any of the disjuncts, and the conclusion merely expresses whatever follows from its affirmation or denial. Both the minor premise and the conclusion are categorical propositions. It was mentioned that a true disjunctive proposition is one whose disjuncts exclude each other.

 Rules: (Complete disjunction)

In the case of complete disjunction whose parts are mutually exclusive, i.e., the contradict each other, the following rules apply:

 Rules:Posit one alternative, sublate the other. (Ponendo-tollens)Sublate one alternative, posit the other. (Tollendo-ponens)

**Posit one alternative, sublate the other. (Ponendo-tollens) 

The minor premise affirms one disjuncts and the conclusion rejects the other.

Examples:

The accused is either guilty or not guilty;

But, he is guilty; (affirmed)

He is not not guilty. (rejected)

 

The accused is either guilty or not guilty;

But, he is not guilty; (affirmed)

He is not guilty. (rejected)

 

 

**Sublate one alternative, posit the other. (Tollendo-ponens) 

The minor premise rejects one disjuncts and the conclusion affirms the other.

Example:The military operation in Basilan is either successful or unsuccessful;But it is not successful; (rejected)It is unsuccessful. (affirmed)

 The military operation in Basilan is either successful or unsuccessful;But it is not unsuccessful; (rejected)It is successful. (affirmed)

Rules: (Incomplete disjunction)In incomplete disjunction whose parts are not mutually exclusive, i.e., they don’t contradict each other, these rules apply:

 Rules:Posit one alternative, sublate the other. (Ponendo-tollens)Sublate one alternative, no conclusion. 

** Posit one alternative, sublate the other. (Ponendo-tollens) The minor premise affirms one disjuncts and the conclusion rejects the other. Examples:

The test is either easy or difficult;But it is easy; (affirmed)It is not difficult. (rejected)

 The test is either easy or difficult;But it is difficult; (affirmed)It is not easy. (rejected)

**Sublate one alternative, no conclusion. The minors premise rejects one disjuncts and the conclusion affirms the other. Example:

The test is either easy or difficult;But it is not easy; (rejected)It is difficult. (affirmed)

The conclusion, “It is difficult” does not necessarily follow from the premises. Why? Because the test can be average, in which case it is neither easy nor difficult. This forms the Fallacy or Tollendo-ponens,a fallacy committed when one disjuncts in an incomplete disjunction is rejected in the minor premise and the other is affirmed in the conclusion.

 Example:

This machine is either light or heavy;But it is not heavy; (rejected)It is light. (affirmed)

 This syllogism is invalid. The machine may be moderate in weight.

Different Patterns of the Disjunctive Syllogism

 

It is for the posit-sublate process and the sublate-posit process.

 

A = first disjunct B = second

The relation that exists between A and B in disjunction is expressed by the wedge (v). 

 

Conjunctive Syllogism

Conjunctive SyllogismIt is one whose major premise is a conjunctive proposition consisting of

alternatives (conjuncts), while the minor premise affirms or denies any of the conjuncts, and the conclusion merely expresses whatever follows from its affirmation or denial. Both the minor premise and the conclusion are categorical propositions. It was mentioned that a true conjunctive proposition is one whose alternatives are incompatible.

 Rules:Posit one alternative, sublate the other. (Ponendo-tollens)Sublate one alternative, no conclusion.   Posit one alternative, sublate the other. (Ponendo-tollens) The minor premise affirms one conjunct and the conclusion rejects the other.  Example:

The passenger cannot be in the tricycle and in theBus at the same time;But, he is in the tricycle; (affirmed)He is not in the bus. (rejected)

 

Sublate one alternative, no conclusion 

From the falsity of one conjunct, the truth of the other does not necessarily follow.

  Example:

The passenger cannot be in the tricycle and in theBus at the same time;But, he is not in the tricycle; (rejected)He is in the bus. (affirmed)

  The conclusion, “He is in the bus” does not follow from

the premise. There are vehicles other than the bus that he can take. This fallacy is called the Fallacy of Tollendo-Ponens.

The End