There are definitions for Self, Non Self and the Discriminative Intellect in the First Science.
The Non Self is defined
Everything from the Macrocosm, the Universe
To everything in the Microcosm, Man !
All emotions, all thought processes,
Is called the Non Self, O Noble One !
The Discriminative Intellect is Prajna and it is defined thus
That which distinguishes the Real from the Unreal
That which recognises the Self ultimately
That which differentiates Being from Non Being
Such an intellect is Prajna, O Noble One !
The Self is defined thus
Attributeless, actionless, eternal
Devoid of thoughts, forms
Without emotions, without persona
Ever liberated is the Self Absolute !
These three definitions are the base of the First Science, the Philosophia Prima