for every ability they gain they must lose the service of 1 of their followers, and for every four abilities gained 1 point of strength is permanently lost.Magic-Users:
for with each psionic ability gained the magic-user will lose the ability to remember a spell. That is, with gaining of the first ability the magic-user will be able to use one less 1st level spell, when the second ability is gained he will lose two additional spell levels (i.e. two 1st level spells or one 2nd level spell), and so on. At no time may the magic-user remember more high level spells than low level ones, and if he is able to use 6th level spells, for example, and he selects one, he must be able to remember at least one spell of each of the other five levels.Clerics:
for every psionic ability gained the cleric will lose two of his other advantages. First, he will lose one spell, exactly the same as a magic-user loses spell ability. Second, the cleric loses the ability to turn away undead monsters as he gains psionic powers, so that for each psionic ability gained the cleric ranks a level lower in the ability to turn undead. Thus, a 10th level cleric with four psionic abilities would have a loss of 10 spell levels and turn undead as a 6tyh level cleric.Thieves:
In addition to the penalties noted for fighting men, however, thieves also lose 1 point of dexterity for each four psionic abilities gained.Say what you will about the efficacy of these proposed balancing factors but they're actually quite interesting. For example, psionic ability would seem to be at odds with magic, since an increase in psionic potency is met with a concomitant decrease in magical potency. Psionic ability also somehow weakens the physical body, as evidenced by the loss of Strength and Dexterity by fighting men and thieves (There's also the implication that thieves are a sub-class of fighters but that's a different topic). Finally, there's the decrease in a cleric's ability to turn the undead the more psionically powerfully he becomes. What's up with that?
Again, I'm not certain that these penalties for possessing psionics make up for the benefits gained, but there's no question that they're very suggestive about the metaphysics behind psionics. With the exception of the undead aspect, there's even a certain logic to it all (and there may even be with the undead, though I haven't yet figured it out). Any new psionics system would be wise, I think, to look to Supplement III for inspiration, even if using different details. I like psionics to feel odd and alien and somehow contrary to the ordinary rules of the D&D world. That's part of what makes them compelling to me and why I think they deserve their own mechanics, distinct from those of spellcasting.