Didn't I once say these terms, "brawler" and "beat-'em-up", were synonymous? Well, they're not, I was wrong, and I'm going to redefine and clarify them moving forward. This is more than a matter of arbitrarily distinguishing terms just to make my own language clearer, it's about distinguishing a type of game from a type of gameplay. A historically established genre from an observationally established classification.
Let's start with "beat-'em-up". This is a pretty well-known term that I'm going to borrow from the mainstream and use in the traditional sense. It refers to a style of game rather than a style of gameplay, one built on the traditions of Renegade, Double Dragon, and Final Fight. A beat-'em-up is just a game that looks and is structured like these games - a combat-driven sidescroller set on a limited X-Y plane (usually presented isometrically) that pits the player in a series of arena battles. Why are these games beat-'em-ups? Because that's what they've come to be called. It's not a constructive term, it's a high-level label. There could be anything underneath the skin of a beat-'em-up - Bucky O'Hare is a shooter, Castle Crashers is an action RPG, and Double Dragon is a brawler. The beat-'em-up could use multiple styles of gameplay, too - Alien Storm's got brawling, scrolling shooting, and gallery shooting; Battletoads has hyperspeed vehicle platforming levels. But there's little denying that the favorite style of gameplay for the beat-'em-up is brawling, and therein lies the confusion of terms.
|Final Fight, the archetypical beat-'em-up. All beat-'em-ups look essentially like this.|
And what, again, is "brawling"? That's a style of gameplay built around one-on-one melee combat with reactive (counter-based) foes. And as we've said previously of the translation from style of gameplay to genre of game (paragraph 2), a "brawler" is just a game that develops brawling as its primary mechanic. So a brawler is a combat action game where most ("most" being subjective of course) of the challenge and interest comes from independently threatening foes. Why are these games brawlers? Because they are intrinsically linked by shared gameplay fundamentals.
That means many beat-'em-ups are in fact brawlers, like River City Ransom, Final Fight, and Streets of Rage. In fact it's no surprise that the beat-'em-up was a favorite of fighting game developers like Capcom and SNK, as brawling is closely linked to one-on-one fighting games.
|Double Dragon is a beat-'em-up made up almost entirely of brawling|
But it's possible to have a beat-'em-up that isn't a brawler, like Bucky O'Hare, a shooter that only looks, but doesn't play, like Final Fight. Faster, wider beat-'em-ups with long enemy lists like Turtles in Time and X-Men never seemed like brawlers to me (though I'd have to play them more to truly get a feel for whether the enemies are well-rounded or if the challenge is coming from structured setups).
|Bucky O'Hare is a beat-'em-up built around shooting and platforming instead of brawling|
And it's also possible to have a brawler that isn't a beat-'em-up, like Red Steel 2, a first-person sword-fighting game that's all about dueling gangs of enemies... but looks/controls nothing like Final Fight. In fact I wrote an entire three part feature about first-person brawlers a while back.
|One of my favorite brawlers of all time is Zeno Clash, which isn't a beat-'em-up at all|
So they're related ideas, there's no doubt. And it's no mistake that they can be used interchangeably to refer to the same game. The idea is simply that one is a surface level description that doesn't tell you about how the game plays - in that sense, the beat-'em-up is a wide open genre in that you can do anything with it (and it's that much more disappointing that 90% of them are generic brawlers). The other identifies a kindred spirit that ran through many beat-'em-ups but transcends a historical movement or any singular style of presentation.