It's all in the hops
No, IPA is a beer of today. It was inspired by the idea of those old ales, of beers that were robust and heavily hopped. They were modernised in the 1980s and again in the 2000s, and now again in the twenty-teens by the citrusy, tropical, resinous and bold hops of Northwest America and how they taste best when you drink them fresh.
IPA now means one thing: hops. Lots and lots of fragrant, bright, citrusy hops. And we typically need a prefix to tell us what to expect in what’s become a big family of hop-forward beers: American IPA, Double IPA, Triple IPA, Session IPA, New England IPA, DDH IPA, Red IPA, Sour IPA, Fruit IPA, and all the rest.