Today I was idly perusing the AD&D 2nd Edition Psionics Handbook and wondering what exactly it is about psionics that didn't quite work. Partly it's the complexity - I remember having a devil of a time figuring out how telepathic combat was supposed to work - but mostly I think it's because it isn't at all seamless with what D&D is trying to achieve. Which may seem like an odd thing to say, because D&D has never been Ron-Edwards-Coherent, but what it was during the TSR era was consistent in feel. Part of that came from aesthetics, philosophy of play, and so on, but partly it also came from the rules, and the psionics rules just weren't of a piece with the rest of the game. Instead of the Vancian magic system that existed for mages and the simple number-of-spells-per-day system for priests, instead you suddenly had to start thinking about Psionic Strength Points. Instead of spells being automatically successful, instead psionic powers were quasi-proficiencies which might succeed or fail.
But on the other hand, perversely, psionic powers were at the same time too much like magic. In the final analysis what you could do with psionics was not much different to what you could do with magic, and most of the book was just a big list of different 'powers' which may as well have just been a big list of new spells for wizards. It seemed, for want of a better term, a bit half-arsed.
Which is a shame. What I want in a psionics system is freedom. Whereas having predetermined spells that you have to learn out of a book, or be granted to you by a god, it makes much more sense to me to have a psionics system in which there are much fewer limits - the player is freer to use his imagination in manipulating reality with his mind, which is kind of the point. So instead of a psionic "school" of telekinesis with a limited number of powers, your character just has telekinesis and can do with it what he wants - does he want to fly? Push a tree over? Pick up a rock and fling it? Make the individual atoms in a stick of wood agitate until the wood bursts into flames? Fine, provided he simply makes an appropriate sacrifice. Or, your character has clairsentience - this means he can practice clairvoyance or clairaudience, stretch his mind into the future or past, see behind a wall into the next bedroom or see what is happening a continent away. Again, provided he makes an appropriate sacrifice.
What's an appropriate sacrifice? Since hit points measure physical and mental strain, simply reduce the psionicist character's hit points according to the 'strength' of whatever he's trying to do. Fling a rock? 1 hp. Move a mountain? That's more like 50.