This is why we cannot measure forces in terms of an abstract unity, or determine their respective quality and quantity by using the real state of forces in a system as a criterion. We have said that active forces are the superior, dominant and stronger forces. But inferior forces can prevail without ceasing to be inferior in quantity and reactive in quality, without ceasing to be slaves in this sense. One of the finest remarks in The Will to Power is: "The strong always have to be defended against the weak" (VP I 395). We cannot use the state of a system of forces as it in fact is, or the result of the struggle between forces, in order to decide which are active and which are reactive. Nietzsche remarks, against Darwinism and evolutionism, "Supposing, however, that this struggle exists — and it does indeed occur — its outcome is the reverse of that desired by the school of Darwin, of that which one ought perhaps to desire with them: namely, the defeat of the stronger, the more privileged, the fortunate exceptions" (TI, "Expeditions of an Untimely Man" 14 pp. 75-6). It is primarily in this sense that interpretation is such a difficult art — we must judge whether the forces which prevail are inferior or superior, reactive or active; whether they prevail as dominated or dominant. In this area there are no facts, only interpretations. The measurement of forces must not be conceived of as a procedure of abstract physics but rather as the fundamental act of a concrete physics, not as an indifferent technique but as the art of interpreting difference and quality independently of fact. (Nietzsche sometimes says; "Outside of the existing social order". VP III 8).
This problem reopens an old argument, a famous debate between Callicles and Socrates (Gorgias; discussion on "nature and convention", 481-527). The resemblance is so striking that it seems to us that Nietzsche is close to Callicles and that Callicles is immediately completed by Nietzsche. Callicles strives to distinguish nature and law. Everything that separates a force from what it can do he calls law. Law, in this sense, expresses the triumph of the weak over the strong. Nietzsche adds: the triumph of reaction over action. Indeed, everything which separates a force is reactive as is the state of a force separated from what it can do. Every force which goes to the limit of its power is, on the contrary, active. It is not a law that every force goes to the limit, it is even the opposite of a law. — Socrates replies to Callicles that there is no way of distinguishing nature and law; for the weak can only prevail if, by banding together, they can form a stronger force than the strong. Law triumphs from the point of view of nature itself. Callicles does not complain of not having been understood, he begins again. The slave does not stop being a slave by being triumphant; when the weak triumph it is not by forming a greater force but by separating force from what it can do. Forces must not be compared abstractly; from the point of view of nature concrete force is that which goes to its ultimate consequences, to the limit of power or desire. Socrates objects a second time; "what matters for you Callicles is pleasure ... You define all good in terms of pleasure."
We can see here what happens between the sophist and the dialectician, on which side the good faith and the rigorous reasoning is. Callicles is aggressive but has no ressentiment. He prefers to give up talking because it is clear that Socrates does not understand the first time and the second time speaks of something else. How can he explain to Socrates that "desire" is not the a**ociation of a pleasure and a pain, the pain of experiencing it and the pleasure of satisfying it? How can he explain that pleasure and pain are reactions, properties of reactive forces, the proof of adaptation or lack of it? And how can Socrates be made to understand that the weak do not form a stronger force? Socrates has partially misunderstood and partially misheard — he is too full of dialectical ressentiment and the spirit of revenge. He who is so exacting towards others, so fastidious when they reply to him...