The cat and the hamster

About this video

Nina has just got a hamster. Our cat loves going out in the garden, she says, and a hamster is a furry pet, just like a cat, so the hamster will love the garden too. Her mum looks worried. This is an argument from analogy: two things are alike in some ways, so they are probably alike in another way too. It is not a proof; like learning from examples, it can only make a conclusion likely.

Whether it works depends on which likenesses and differences there are, and whether they are connected to the conclusion. Being furry has nothing to do with enjoying a garden. And the differences matter a lot: a hamster is tiny, it can't climb back over a fence, and birds and cats hunt animals its size. So Nina's argument is weak.

Compare: last winter the pipe in Gran's shed froze and burst; our shed has the same kind of pipe, no heating, and is in the same cold town; so our pipe could burst too. Here the likenesses are exactly the ones that make pipes freeze, so the argument is strong. The test this animation ends on: is the way they are alike connected to the conclusion, and do any differences matter for it? This video goes with the Just Like... lesson of Logic Level 2 on Knaph.

Transcript

1. 0:00A hamster is furry, just like a cat. So it'll love the garden too!
2. 0:05Alike in being furry. But tiny, can't climb a fence, hunted by cats and birds.
3. 0:12The differences are exactly about going outside. Weak.
4. 0:17Gran's shed pipe burst. Ours has the same pipe, no heating, the same cold. Strong.
5. 0:26Ask, is the likeness connected to the conclusion?
6. 0:31Alike in the ways that matter, or not at all.