Conditional Syllogism
Rules for Conditional Syllogisms
Enthymemes
Pollysyllogisms
What is Conditional Syllogism?
It is a syllogism in which the major premise is a conditional statement.
What is a conditional statement?
It is a compound statement which asserts that one member (the then clause) is true on condition that
the other member (the if clause) is true.
Example A:
If X fell from a tall tree, then he must have been injured.
*The if clause is called the antecedent, while the then clause is called the consequent.
Other examples:
The fact that she is a native of Bohol implies that she knows where the Chocolate Hills are.
(If she is a native of Bohol, then she knows where the Chocolate Hills are.)
In case one of the grantees changes his/her mind, you will get the scholarship.
(If one of the grantees changes his/her mind, then you will get the scholarship.)
The sequence between the antecedent and the consequent, that is, the truth of the consequent follows
upon the fulfillment of the condition in the antecedent. It does not matter whether individually the
antecedent or consequent is true or false; what matters is the relationship between them.
The conditional syllogism can be symbolized by the following:
A - for the antecedent
C - for the consequent
~ - for the negation of the statement
> - for “implies”
- - for “therefore”
Rules of Conditional Syllogism
There are two valid forms of conditional syllogisms; modus ponens and modus tollens.
Example of Modus Ponens:
If it rains, then the ground will be wet. A>C
It rained. A
Therefore, the ground is wet. C
*When the minor premise affirms the antecedent and the conclusion must affirm the consequent.
Example of Modus Tollens:
If it rains, then the ground will be wet. A>C
The ground is not wet. ~C
Therefore, it did not rain. ~A
*When the minor premise denies the consequent, the conclusion must deny the antecedent.
A conditional syllogism is invalid if the minor premise denies the antecedent. This invalid form is called
the fallacy of denying antecedent.
If it rains, then the ground will be wet. A>C
It did not rain. ~A
Therefore, the ground is not wet ~C
The minor premise affirms the consequent. This invalid form is called the fallacy of affirming the
consequent.
If it rains, then the ground will be wet. A>C
The ground is wet. C
Therefore, it rained. A
Enthymeme
What is an Enthymeme?
it is a rhetorical device like syllogism and is known as truncated or rhetoric syllogism. Its purpose
is to influence the audience and allow them to make inferences.
Enthymeme vs Syllogism
Enthymeme is like syllogism, yet different. The difference is that a syllogism is a deductive logic
that contains three parts; the major premise, the minor premise, and the conclusion. Enthymeme on the
other hand, has an implied premise.
All birds have feathers. (major premise)
Kiwis have feathers. (minor premise)
Therefore, kiwis are birds. (conclusion)
vs.
He could not have committed this crime. (major premise)
I have known him since he was a child. (minor premise)
Polysyllogism
What is a polysyllogism?
It is a series of syllogisms in which the conclusion of one syllogism supplies a premise of the next
syllogism. It is used when there are several steps needed to reach a desired conclusion.
Examples:
It is raining.
If we go out while It is raining we will get wet.
If we get wet, we will get cold.
Therefore, if we go out we will get cold.
All lions are big cats.
All big cats are predators.
All predators are carnivores.
Therefore, all lions are carnivores.
Sources:
Legal Logic (Evangelista, F.J. and Aquino, D.R., 2015)
literarydevices.net/enthymeme
en.wikipedia.org/wiki/polysyllogism
