An Introduction to Critical Thinking and Creativity - always yours

EVALUATING ANALOGICAL ARGUMENTS 197
erties that support the conclusion. This is perhaps the most important part of analogical
reasoning because it helps us understand why an analogy is supposed to
work. The argument must highlight important aspects of similarity, if the analogy
plays any role at all in supporting the conclusion. Then you can start evaluating
the argument, using the principles below.
21.1 EVALUATING ANALOGICAL ARGUMENTS
There is no mechanical method for evaluating analogical arguments, but here is a
checklist of the main criteria:
• Truth: Are the two things really similar in the way described? Obviously, an
argument is not acceptable if it has a false premise. In the third argument
above, if it turns out that you do not like outdoor activities and much prefer
sleeping in bed, then you are not like my friend and the argument should be
rejected.
• Relevance: Are the shared properties relevant to the conclusion? Even when
the source and target are similar, the properties they share must be relevant
to the conclusion for the analogical argument to be acceptable. In other
words, having the shared properties increases the probability of having the
inferred property. To use a concrete example, suppose we change the third
argument above slightly:
You are just like my friend since you both like to eat chocolates.
My friend likes rock climbing.
You will also like rock climbing.
This is clearly a lousy argument, even if the premises are true. A preference
for chocolate does not make a person more likely to enjoy rock climbing. In
other words, the common property is simply irrelevant to the inferred property.
Notice that we need to use our commonsense and background knowledge
to determine relevance. It is not enough to focus on the argument
only. For example, if scientists discover that the majority of people who
like chocolates actually enjoy rock climbing, then our background knowledge
has changed, and this argument would become more convincing. This
shows that analogical reasoning is typically a kind of inductive reasoning.
• Number and diversity: Are there many shared properties of different types?
The strength of an analogical argument depends not just on the relevance
of the shared property. The number of shared properties makes a difference
also. If both you and my friend enjoy outdoor activities, and in addition you
are both agile, with good physical strength and balance, then it is more likely
that you will like rock climbing. In short, finding more relevant properties
shared by the source and the target can strengthen an analogical argument.