An analogy is a comparison that shows how seemingly different things are similar in some relevant way. They can be extremely helpful for relating new or complex ideas to people, because you can draw connections to things with which they’re already familiar.
Analogies can also be amusing methods of description that stretch our imaginations. Consider this example, from newspaper columnist Sydney J. Harris’s "What True Education Should Do:"
“Pupils are more like oysters than sausages. The job of teaching is not to stuff them and then seal them up, but to help them open and reveal the riches within. There are pearls in each of us, if only we knew how to cultivate them with ardor and persistence.”
The comparison here tells us something important about how the author believes teaching should work: not by bombarding a student with facts or by rote memorization (“stuffing” them), but rather by fostering their own inner strengths and skills.
Note also that this analogy reveals a secondary belief: Harris contrasts a view of education as being externally-based with one he prefers in which it is internally constructed.
The trick to building a successful comparison is making sure that the similarities between two things are relevant to both of them. If the elements aren’t important to both, then the analogy falls apart without illustrating anything.
This analogy was presented by a commenter in response to a blog post about nuclear energy:
“Talking about use of nuclear energy is like terminating the human race, think about the effects it would have on the human body, the massive radiations released from the fusion of atoms can cause lifelong mutations that can be transferred from generation to generation.”
The comparison here is supposedly between “talking about use of nuclear energy” and “terminating the human race.”
Why does the commenter think these two things are similar? He offers two reasons. First, there are effects on the human body from nuclear radiation.
That’s true, if the radiation is poorly contained. But nuclear energy doesn’t guarantee catastrophic human exposure to radiation.
Even less clear is the effect that terminating the human race has on our bodies. One would assume that it wouldn’t be pleasant, but that’s hardly helpful to understanding his point.
The second reason that this commenter uses to justify his analogy is that genetic mutations “can be transferred from generation to generation.”
Aside from the fact that most mutations that arise from exposure to radiation make reproduction difficult, if the human race were terminated, there would be no new generations to pass mutations on to. This part of the analogy doesn’t even make sense.
A weak analogy doesn’t necessarily mean that a person’s ideas are invalid. Some concerns over the drawbacks of nuclear energy are definitely worth discussing, even if this particular commenter failed to articulate them intelligibly.
Still, the first step to convincing someone else to listen to you is logical consistency. If you can’t explain your position properly, then you can’t expect anyone else to agree with it.