Decades ago, when I was little, I read this joke in Mad Magazine:
Do your feet smell? Does your nose run? You may be built upside-down.
I giggled for a short time — just a couple of days, I think — at the surprising coincidence of the two verb senses, and the double pun, and then got on with whatever boys in short pants do during those parts of the day that are not taken up with giggling. But I see now that there is something linguistically interesting about the joke: the two questions convey the effect of a conditional. So the content of the joke could be phrased (though for some reason much less amusingly) like this:
If your feet smell and your nose runs then you may be built upside-down.
This similarity of effect between interrogative clauses and conditional clauses has a connection to the historical reason for an identity of form between the words introducing the interrogative subordinate clause in (1) and the conditional clause in (2).
(1) I don't know if the car will start.
(2) We won't go if the car won't start.
The two ifs share an etymology, but they have grown apart.
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