> I’m no philosopher, but if your argument hinges on moving goalposts until purity is reached, and your basic assumption is that the requirements for purity are

> I’m no philosopher, but if your argument hinges on moving goalposts until purity is reached, and your basic assumption is that the requirements for purity are infinite, then it’s not a very useful argument. I imagine many definitions are initially rather broad and only get refined down over time. Laertius gives us a classic example: > Plato defined man thus: “Man is a two-footed, featherless animal,” and was much praised for the definition; so Diogenes plucked a cock and brought it into his school, and said, “This is Plato’s man.” On which account this addition was made to the definition, “With broad flat nails.” I don’t think it’s correct to think of that as infinitely moving goalposts, however. More that the weakness of definitions isn’t always immediately transparent.