Last year, I reviewed a book that contained style guidelines for beer. Usual enough, but these came from the Beer Judge Certification Program (BJCP)--which is not usual. Google "beer styles" and the BJCP's are the third option. There's a BJCP app. As the public gets more and more familiar with the idea of beer style, they look to a guide to describe what a doppelbock is or what distinguishes a saison from a biere de garde. I tend to get a lot of blowback when I suggest it, but for those people, the BJCP guidelines cause more harm than good.
Let's start with the broadest critique first: there's no such thing as style. What we refer to styles are useful categories that help us understand general characteristics about beer. But styles are not, like humulus lupulus, genetically-specific species that can reside happily in taxonomic perpetuity. A style is more like an ethnography; it gathers together the incomplete, blurry, and constantly-changing history of the style and offers a provisional designation.
Almost everyone, encountering the concept of beer styles for the first time, thinks they represent unanimous consensus and are fixed. Like the ancient wine appellations of Europe, to know what a mild ale is now is to know what it was in London two hundred years ago. But since beer is a recipe-based beverage and a commercial product, styles fluctuate constantly. Most styles look different today than they did 100 years ago.
To narrow the critique a bit, the trouble grows when we begin to parse the larger categories (which do have historical and regional significance) into small sub-categories. For the BJCP, there's a method to this madness; they're trying to offer guidelines so that judges can evaluate several beers in a flight. Yet the division into sub-categories is mostly an artificial process of distinguishing between categories of beers that have no historical or regional distinction and which may not vary much at all by gravity or ingredients. Even the BJCP recognizes this reality: "Many styles are quite broad and can encompass multiple stylistically accurate variants."
In the context of a judging panel, there have to be criteria. But the descriptions that appear in the BJCP aren't prescriptive, they're descriptive--a fact almost certainly lost on most average beer drinkers. There's nothing innate about "English pale ales" as written in the BJCP. I wish people would hold these concepts lightly and leave them behind when they don't seem useful.
Let's say you've got an amber lager in front of you and you'd like to know if it's supposed to be a Vienna lager or a marzen. It's fantastic to understand what distinguish those two styles historically, and to know how the development of Vienna and Munich roasts help define the malts that made them famous. But let's say that beer was brewed stronger than either style and made with American hops (which, if you're sitting in an American brewpub, will likely be the case). In the context of judging the beer, you might be able to say whether it's brewed "to style," or not, but so what? At this point in your tasting experience, the idea of trying to match it to a style is just a distraction.
Anyway, I wish the BJCP guidelines were less broadly available and average drinkers were mainly consulting guidelines that were broader, had more (and better*) histories, and less technical. The BJCP guidelines are great for judges, but not so good for the public.
*Each style described in the BJCP guidelines is accompanied by a brief history, and many are pretty bad. I wish they'd clean them up--at this point, good, reliable historical research is broadly available.