Analogies

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.

- What is x in analogy a? What is y? What is A?
- 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.