Analogy

In argument by analogy the speaker attempts to prove that because certain things are known to be true in something that can be observed they are likely to be true in something else which in so far as it can be observed is quite like the first. We continually argue by analogy in daily life.

Lincoln was really using analogy when he replied to the urging to change his army leaders during the Civil War, that he didn't think it wise to "swap horses while crossing a stream." Scientists use this method to draw conclusions when it is impossible to secure from actual observation or experiment a certain last step in the reasoning. The planet Mars and the earth are similar in practically all observable matters; they are about the same distance from the sun, they have the same surface conditions. The earth has living creatures upon it. Hence—so goes the reasoning of analogy—Mars is probably inhabited.

Reasoning by analogy is used to prove that universal suffrage is good for the United States because it has been good for one particular state. A student may argue by analogy that the elective system should be introduced into all high schools, because it has been followed in colleges. It may be asserted that a leading bank president will make a good university president, because he has managed one complex institution. The essence of all good reasoning by analogy is that the two things considered must be so nearly alike in all that is known that the presumption of belief is that they must also be alike in the one point the arguer is trying to establish. This is the test he must apply to his own analogy arguments.

 

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