Psionic Ability

Psionic Ability or PSI is one of the basic statistics in System Shock 2.

Overview
The maximum effective Psionic Ability level is 10, although most Psionic skills benefit from a PSI up to 8. The player can only permanently upgrade Psionic Ability to level 6, while the next two levels require a combination of the following items/Psionic Disciplines:
 * A PsiBoost™ Implant (+1)
 * A Psi Booster (+1)
 * A WormSkin Armor (+2)
 * Recursive Psionic Amplification (RPA) (+2)

Overloading a Psi Power casts it with a bonus of +2, to a maximum effective PSI of 10 (player needs to have PSI 8 already before casting to reach PSI 10). It is not possible to reach PSI 9 or 10 without Overloading.

Psionic Ability increases the Psi Points of the player and influences the duration/effectiveness of Psionic Disciplines. The amount of bonus Psi Points given depends on the difficulty:

Psionic Ability vs maximum Psi Points Table

 * Maximum Psi Points of the player change when upgrading the PSI stat, but they are not affected in any way by the items, RPA, nor overloading.
 * The only other thing affecting the player's maximum Psi Points is unlocking main Tiers of Psi Powers. Each Tier adds to the max Psi Points a value of 2x the level of the Tier (no matter the skill level), e.g. Tier 3 adds 6 to the max Psi Points. The total bonus to max Psi Points is thus 30.

Псионика