Categorical Syllogisms

If an argument has two categorical premises and a categorical conclusion, and the two categorical premises jointly support the conclusion, then this argument is a categorical syllogism.

Example:

All mammals are animals that breathe by means of lungs.
All whales are mammals.
Therefore, all whales are animals that breathe by means of lungs.


Comprehension Questions
1 What kind of propositions are the premises of a categorical syllogism?
a) hypothetical and categorical
b) disjunctive and categorical
c) categorical only
d) all of the above
2 A categorical proposition is
a) a proposition that makes an assertion about the relations of classes
b) a proposition that asserts that the truth of one proposition is sufficient for the truth of another
c) a proposition which asserts that either one or another of two propositions is true
3 How do the premises support the conclusion in a categorical syllogism?
a) jointly
b) independently
c) either jointly or independently
4 Is the following argument a categorical syllogism?

If you play with fire, you will get burned.
You played with fire.


You got burned.
a) Yes
b) No
5 Is the following a categorical syllogism?

No horned animal is a carnivore.
All moose are horned animals.


No moose is a carnivore.
a) Yes
b) No
6 Is the following argument a categorical syllogism?

Either my book is in my bag or I left it in the library.
My book is not in my bag.


I left my book in the library.
a) Yes
b) No
7 Is the following argument a categorical syllogism?

All supporters of the nuclear freeze want to preserve peace.
No conservatives support the nuclear freeze.


No conservatives want to preserve peace.
a) Yes
b) No


Structure of a Categorical Syllogism

© Copyright 1998, W.W. Norton & Co.