alteritynuzlocke:

In Alterity, TMs and HMs are move licenses. “This Pokemon is now allowed to use this move in-battle.” That’s it. No magical rays of light, no rewriting of DNA. The license disc contains the League’s official move specs and some basic instructional material, but it’s up to the trainer and the Pokemon to physically master the move, same as any other battle technique. It can take minutes, or days, or years. Some Pokemon never manage to learn the more arcane ones.

Just because the species is supposedly able to learn a technique doesn’t mean every individual can actually do so, just like not every human can learn advanced physics or bench press 500 lbs. Several of the ‘allowed’ TMs make no sense at all for certain species and are pretty much impossible to learn. On the opposite end, there are a lot of cool things Pokemon can do that they are not actually allowed to use in an official League battle, because the technique doesn’t fall within the limits of an ‘official’ move.

(HMs have an additional function in that their out-of-battle use is strictly regulated and pretty much the cornerstone of the economy, but that’s a post for another day.)