5.4: Analogy

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Analogies are comparisons between two things to help in clarification or explanation. They can be used as simple illustrative tools to aid in understanding, like how you might explain to someone that rollerblading is like ice skating on hard, dry surfaces. We use analogies all the time, but for the current lesson, the focus will be on using analogies to make arguments.

An argument from analogy generally has the following form:

- A has properties P,Q,R… - B,C,D… have properties P,Q,R… - B,C,D… also have property Z - Therefore, A probably has property Z

That might make it sound more complicated than it actually is, but that’s the technical way in which they work. You observe that something has certain properties, you then observe that something else has many similar properties, AND they have more properties, so that first thing probably has the property as well. For example,

- In-line skating has all the wheels in a line and requires very good balance. - Ice skating has one blade in a straight line on each skate, requires very good balance, and I’m very bad at it. - Therefore, I am probably very bad at in-line skating.

Or,

- Playing Skee-Ball requires you roll a ball at a target and that makes it fun. - Bowling requires that you roll a ball at a target, so that probably makes it fun, too.

When making an argument from analogy, you should always remember to consider important disanalogies, because one important disanalogy can make the argument fall apart. For an analogy to work, all of the aspects that are being compared need to be true, relevant, important, and absent any important disanalogies! So, is the following a good analogy?

- Cars pollute a lot, so Tesla Roadsters pollute a lot.

Generally, arguments from analogy are stronger when there are more and closer analogies used in the argument (and Tesla Roadsters have a lot of similarities with regular cars), but a single important disanalogy (Tesla Roasters are electric cars) can destroy the argument.

What makes arguments from analogy better?

1) The argument cites more and closer analogies that are more important 2) There are fewer or less important disanalogies between the object in the conclusion and the other objects 3) The objects cited only in the premises are more diverse. 4) The conclusion is weaker

As an exercise, make an argument by analogy and then go about modifying it. How can it be made stronger? Why will that make it stronger?

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