A "thing-in-itself" is just as absurd as a "sense-in-itself," a "meaning-in-itself." There is no such thing as a "fact-in-itself," for a meaning must always be given to it before it can become a fact.
The answer to the question, "What is that?" is a process of fixing a meaning from a different standpoint. The "essence" the "essential factor," is something which is only seen as a whole in perspective, and which presupposes a basis which is multifarious. Fundamentally the question is "What is that for me?" (for us, for everything that lives, etc. etc.).
A thing would be defined when all creatures had asked and answered this question, "What is that?" concerning it. Supposing that one single creature, with its own relations and standpoint in regard to all things, were lacking, that thing would still remain undefined.
In short: the essence of a thing is really only an opinion concerning that "thing." Or, better still; "it is worth" is actually what is meant by "it is" or by "that is."
One may not ask: "Who interprets, then?" for the act of interpreting itself as a form of the Will to Power, manifests itself (not as "Being," but as a process, as Becoming) as a passion.
The origin of "things" is wholly the work of the idealising, thinking, willing, and feeling subject. The concept thing as well as all its attributes.—Even "the subject" is a creation of this order, a "thing" like all others: a simplification, aiming at a definition of the power that fixes, invents, and thinks, as such, as distinct from all isolated fixing, inventing, and thinking. Thus a capacity defined or distinct from all other individual capacities; at bottom action conceived collectively in regard to all the action which has yet to come (action and the probability of similar action).
557.
The qualities of a thing are its effects upon other "things."
If one imagines other "things" to be non-existent, a thing has no qualities.
That is to say; there is nothing without other things.