THEAETETUS: Certainly not.
SOCRATES: When I perceive I must become percipient of something—there can be no such thing as perceiving and perceiving nothing; the object, whether it become sweet, bitter, or of any other quality, must have relation to a percipient; nothing can become sweet which is sweet to no one.
THEAETETUS: Certainly not.
SOCRATES: Then the inference is, that we (the agent and patient) are or become in relation to one another; there is a law which binds us one to the other, but not to any other existence, nor each of us to himself; and therefore we can only be bound to one another; so that whether a person says that a thing is or becomes, he must say that it is or becomes to or of or in relation to something else; but he must not say or allow any one else to say that anything is or becomes absolutely:—such is our conclusion.
THEAETETUS: Very true, Socrates.
SOCRATES: Then, if that which acts upon me has relation to me and to no other, I and no other am the percipient of it?
THEAETETUS: Of course.
SOCRATES: Then my perception is true to me, being inseparable from my own being; and, as Protagoras says, to myself I am judge of what is and what is not to me.
THEAETETUS: I suppose so.
SOCRATES: How then, if I never err, and if my mind never trips in the conception of being or becoming, can I fail of knowing that which I perceive?