(minor)
|
You are a (middle)
|
true teacher,
∴ (minor)
|
You are (major)
|
sympathetic.
(2) No (major)
|
shell fish are (middle)
|
vertebrates,
All (minor)
|
trout are (middle)
|
vertebrates,
∴ No (minor)
|
trout are (major)
|
shell fish.
The necessity of having but three different terms in any syllogism may be understood by supposing that there are four different terms; then it would follow that there could be no standard or common link. In the axiom, “Things equal to the same thing are equal to each other,” the same thing is the common standard or link. Two things which equal two different things are not equal to each other.
The impossibility of reasoning from four terms may be shown by circles.
All men are mortal.
All trees grow.
FIG. 8.