It's only natural to try to get at the unknown from the known. But it can be dangerous. Consider this:

(a) "The economy is like a stove. A stove overheats when the temperature is too high. So when the economy approaches full employment, we have to cool it down by raising interest rates."

Or another one from the economists:

(b) "The government is like a family. No family can borrow so much and survive. So we have to cut social programs and balance the budget."

Why are these analogies bad? Is it the premises, or the form itself? Or premises in one case and form in another?

The general form of an analogy is:

x is like y

y is A

Therefore, x is A.

  1. What is x in analogy a? What is y? What is A?
  2. What is x in analogy b? What is y? What is A?

This form is invalid. All kinds of silly arguments fit it, including the ones above. A good analogy, which still should be evaluated with care, has the form:

x is like y with respect to being A

y is A

Therefore, x is A.



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