Nyāya Sūtras 200

The means of valid cognition have been examined; now the object of valid cognition is examined. And that begins with the self; therefore the self is investigated: Is the self merely an aggregate of body, sense organs, mind, intellect, and sensation, or is it distinct from them?

Whence is the doubt? Because designation is established in both ways. "Designation" is the expression of the relation of an action and an instrument to an agent.

That is of two kinds: [designation] of a whole by a part—"The tree stands by its roots," "The palace is supported by pillars"; and designation of one thing by another—"He cuts with an axe," "He sees with a lamp." And this designation exists: "He sees with the eye," "He cognizes with the mind," "He deliberates with the intellect," "He experiences pleasure and pain with the body." In that case, it is not determined whether it is [designation] of a whole by a part, namely of the aggregate of the body and so on, or of one thing by another, namely of something distinct from it.

This designation is of one thing by another. Why?

Because of the apprehension of a single object by sight and by touch.

A certain object is grasped by sight, and that same object is grasped by touch as well: "That which I saw with the eye, that very thing I now touch with [the organ of] touch," and "That which I touched with [the organ of] touch, that very thing I now see with the eye." And these two cognitions, having a single object and having a single agent, are synthesized.

And they do not have the aggregate as their agent, nor do they have a single sense organ as their agent. Therefore, that grasper of a single object through the eye and through the organ of touch, who synthesizes the two cognitions having different causes and different agents but having the same object, is the self, which is a distinct entity.

How, then, do they not have a single sense organ as agent? Because a sense organ can synthesize only the apprehension of its own object, having no other agent, but not the apprehension of a different object by a different sense organ. How do they not have the aggregate as agent? Because this single entity experiences the two synthesized cognitions having different causes and having oneself as agent, not the aggregate. Why? For in the aggregate, the non-synthesis of the apprehension of a different object by each individual [component] has not ceased, just as with a different sense organ.