Class Power Source

[Duff]

When 4e was new, they mentioned a "Ki" power source was coming. They later realized that they were starting to pigeonhole Ki as the "Asian" power source.

But ask yourself this about classes and power sources:
This class uses discipline to develop and harness an internal wellspring of power to accomplish things beyond the scope of most people.

Does that describe psions, monks, or both?

Thematically? Could be either. Or sorcerers as Kuruld noted

Mechanically:
Psion - Uses Psi points to enhance their powers
Battlemind - Uses Psi points to enhance their powers
Ardent - Uses Psi points to enhance their powers
Monk - Has the option to use one of their movement powers at the same time they use an attack power