Section 13 is very complicated, very deep, and very important in understanding Nietzsche. The focus is on a contrast between lambs and birds of prey, in order to understand the origin of the concept of "good" as born from ressentiment. It is quite natural that lambs may consider birds of prey to be evil, since they kill and carry off lambs. And from this, it may also be understandable that lambs consider everything unlike birds of prey--themselves, for instance--to be good.
While Nietzsche accepts these conclusions as understandable, he denies that they can be used to reproach or condemn birds of prey for killing lambs. It would be as absurd to ask a bird of prey not to kill as it would be to ask a lamb to kill. Killing is an expression of strength, and it is only through a misunderstanding caused by language that we manage to see the bird of prey as somehow distinct from its expression of strength.
To illustrate his point, Nietzsche takes as an example the sentence "lightning flashes." Grammar would lead us to conclude that there is a subject--"lightning"--and a predicate--"flashes." But what is the lightning if not the flash? Nietzsche argues that grammar, and only grammar, has led us to think of actions in terms of subjects and predicates. In reality, he suggests, "'the doer' is merely a fiction added to the deed--the deed is everything."
Grammar has thus led us to think of a bird of prey as somehow separate from its expressions of strength, and thereby free either to kill or not to kill. On the contrary, Nietzsche suggests, the bird of prey is the strength is the killing. The lamb's morality is in no position to hold the bird of prey accountable for killing: that would be equivalent to blaming it for existing.
When slave morality lauds its conception of "good," praising all those who do not kill, hurt, or offend, it is essentially praising all those who are too powerless to cause any harm for not causing any harm. It interprets the inaction resulting from impotence as a positive, meritorious deed, as enduring ills and leaving revenge to God. Slave morality depends on the belief in a subject (or a "soul") which is independent of its deeds, so that it can interpret its weakness as freedom, and its inaction as praiseworthy.
Section 14 is a rather over-the-top depiction of slave morality being forged in a sweaty, smelly hole full of hatred and muttering. It culminates with the claim that "justice" is an invention of slave morality made out as an ideal that masters brazenly disregard. Slave morality does not seek revenge, but waits for the "Judgment of God" that will restore justice.
Section 15 provides textual evidence from early Christian writings, particularly Tertullian, to show hatred and ressentiment being paraded as "Christian love." These writers expend a great deal of voyeuristic energy inventing all sorts of tortures for sinners not welcomed into the kingdom of heaven.
Nietzsche concludes with the remark that the struggle between "good and evil" and "good and bad" is one of the oldest and greatest on earth, and that the "good and evil" of ressentiment has unquestionably come out on top. He asks, however, if there might be a resurgence of the overthrown master morality, suggesting that we might will this with all our might.
One of the greatest deceptions of language, according to Nietzsche, is the subject-predicate form of grammar. Because all sentences are divided into a subject and a predicate, we are led to believe that there are actors (subjects) and deed (predicates) and that the two can be separated. As a result, we come to think of killing as something distinct from a bird of prey, something that it does. Nietzsche points out that grammar would similarly suggest to us that flashing is something distinct from lightning, something that it does. And just as there is no lightning distinct from the flash, Nietzsche suggests that there is no bird of prey distinct from the killing.
This argument does not simply suggest that killing is in a bird of prey's "nature" and that "it wouldn't be a bird of prey if it didn't kill things." In Nietzschean metaphysics, there is no such thing as the bird of prey as common wisdom would understand it. Gilles Deleuze interprets Nietzsche as suggesting that nothing exists but forces. We might simplify Deleuze's analysis by suggesting that only verbs truly exist: nouns and subjects are just the conveniences of grammar. While we might talk about a bird of prey killing a lamb, really there is just one force acting upon another. Of course, using "force" as a noun is a mistake, as it simply substitutes one noun for another.
This discussion of metaphysics gets very tricky very quickly, and because we are so accustomed to thinking in terms of subjects and predicates, it is very difficult to imagine a world that consists solely of forces acting on one another. Rather than dwell too long on this question, we leave the metaphysics here, encouraging the reader to sort out what consequences this metaphysics might have on our concept of personal identity, epistemology, and much else besides, and to ask whether Nietzsche's account is plausible and how it might be tested. For now, we will focus on the immediate consequences for the moral philosophy Nietzsche is discussing in this essay.
At first glance, it might appear that Nietzsche is denying free will: we cannot hold the bird of prey accountable since it could not act otherwise. On this interpretation, Nietzsche would essentially be claiming that none of us are free to do anything and none of us can be held accountable for anything. This interpretation is about 10% true. To claim that the bird of prey has no free will is about as opposite to Nietzsche's position as can be. Nietzsche would rather claim that there is no bird of prey independent of its will. To talk about a bird of prey as "having" free will is again to make the subject- predicate error. Will is not a "thing" that one "has": a will is, essentially, what one is. The bird of prey is its will, and that will wills the death of the lamb. Not to kill the lamb would require a different will, that is, a different creature altogether. If we say the bird of prey should not have killed the lamb, we are saying that the bird of prey should have been a different animal.
The earlier interpretation was 10% correct in supposing that none of us can be held accountable for our actions. According to Nietzsche, we can't; at least, not in the sense that current law and morality would have us be accountable. Nietzsche suggests that justice, as we understand it, is an invention of the powerless: they are unable to take their own revenge, to make their own right, and so they invent an abstract ideal of "justice" that will prove them right, in heaven if not on earth. According to Nietzsche, we are not accountable to some higher ideal of justice, but we are accountable to ourselves, and if we are worth our salt, we will be far harsher judges than any higher ideal could be. Thus, in Nietzsche's view, murderers who kill for the sake of money do not transgress any external moral code, but they allow themselves to be controlled by money and thereby show themselves to be weak-willed and shallow.
This summary and commentary should make abundantly clear how difficult Nietzsche interpretation can be. We still find ourselves facing many questions: on what standard would Nietzsche judge a murderer to be weak-willed and shallow? If we are nothing more than wills, what does it mean to be weak-willed? And how might Kauffman interpret Nietzsche's closing remark that we should hope that master morality will return to challenge slave morality if Kauffman so firmly insists that Nietzsche is not a defender of master morality? These are just a few of the questions that remain; the commentary that follows will try to make some headway toward possible answers.