An argument is a relationship between a set of premises and
a conclusion. But people rarely express in words all the premises
they are using. Most arguments contain some premises that are
assumed but not stated, implicit rather than explicit.
Suppose we are planning a hiking trip, and I tell you that Sally
can't come because she has a broken leg. My argument clearly
assumes that people with broken legs can't go hiking, but I
didn't state that premise, because it was too obvious.
When we analyze an argument, it is important to identify the
assumed premises. They can then be labeled--using letters
instead of numbers to distinguish them from explicit premises--
and included in the diagram.
There are two basic rules we should follow in interpreting or
analyzing an argument by providing assumed premises:
|1. ||The premise we supply should close the logical gap between the stated premise and the conclusion, and|
|2. ||The premise we supply should not commit us to more than is
Suppose you are taking French, and you learn that some of your
classmates are failing; you infer they they do not enjoy the
subject. The task, now, is to identify the assumed premise in
Consider the following candidates:
A. French is a Romance language.
B. Paris is beautiful in the springtime.
C. People never enjoy something that they find difficult.
D. Students do not enjoy subjects in which they are failing.
Using rule 1, I can eliminate candidates A and B. Neither of them
helps close the gap in the argument as stated; neither
premise is relevant to the conclusion.
Rule 2 helps me choose between the remaining candidates.
Notice that C is a much more sweeping generalization than D;
C applies to all people and all activities, whereas D applies
only to students and the subjects they are studying. Because
premise D closes the gap in the argument, without committing
me to as much as C does, it is the one I should use.