In yesterday’s installment, the two kids of the Lombard family in the comic strip One Big Happy, Ruthie and Joe, advance a devious — and transparently malicious — idea about the pragmatics of conversation. As a slogan,
Two nasties make a nice.
That is, saying two nasty things about someone counts as saying a nice thing about them, yuk yuk. We-e-ell, the kids maintain, with impish speciousness, that that’s just a special case of the general principle that
Two negatives make a positive.
First thing: such a slogan is a highly abbreviated formula in ordinary language of some significant technical principle, the virtue of the slogan being that it is striking and memorable; it’s an aide-memoire. But it’s just a label, and labels are not definitions.
Second thing: the kids’ version exploits a massive ambiguity in the adjectives negative / positive, and a corresponding ambiguity in the verb make. To which I now turn.