30 An Introduction to Clearer Thinking- The alternative syllogism offers in its major premise an
alternative in the “either-or” form: “Either we eat, or we
starve.” One of the alternatives must be true: therefore, if we
show that one of them is false, we prove that the other is true.
A valid argument reads:
Either we eat, or we starve.
We do not starve.
Therefore, we eat.
The major premise is an alternative (either-or) statement.
The minor premise and the conclusion are both categorical
statements, the minor premise denying one of the alterna
tives and the conclusion affirming the other. If the minor
premise affirms an alternative (“we eat”), a fallacy appears:
Either we eat, or we starve.
We eat.
Therefore, we do not starve.
Odd as it may seem in the given context, the conclusion
is not valid, for there is nothing in the premises to assure us
that we cannot eat and also starve. The second premise
commits the fallacy of affirming an alternative. - The disjunctive syllogism has a major premise in the
“not both ...and ...’’form: “Men are not both dishonest and
happy.” One of the two conditions must be false; therefore,
if we show that one of them is true, we show that the other
must be false. A valid argument reads:
We cannot both eat our cake and have it.
We have eaten our cake.
Therefore, we cannot have it.
The major premise is disjunctive; the minor premise and
the conclusion are both categorical—the minor premise
affirming one of the two disjunctive conditions. If the minor
premise denies one of those conditions, the argument com
mits the fallacy of denying a disjunctive.
When one is familiar with the basic concept of syllogistic
logic, an awareness of the problems of clear thinking should be
apparent. This awareness, hopefully, will translate into some
action—further reading in sources that deal with logic and
related subjects. Recently, materials on logic, critical thinking,