The paper starts with some familiar "Alfanoesque bravado": "the Doctrine of Types, as formulated by Leiter, is manifestly unsupported both by Nietzsche's texts and as an empirical hypothesis" (1). Oh goodness! In his paper, Alfano doesn't actually discuss the empirical evidence (though Knobe and I do in "The Case for Nietzschean Moral Psychology"). He does discuss the textual evidence, yet by the end summarizes the view he accepts as follows:
Nietzsche thinks that beliefs and actions, including their moral beliefs and actions, are to be explained largely in terms of their psycho-physical types. Psycho-physical types in turn are to be understood as constellations of largely stable but nevertheless mutable and interrelated drives. (13)I would have thought that was my view, and I'm certainly happy with Alfano's formulation. So where is the disagreement?
My official formulation of the "Doctrine of Types" (NOM, 8) is as follows (Alfano quotes it):
Each person has a fixed psycho-physical constitution, which defines him as a particular type of person.If I understand Alfano correctly, he has two primary, though perhaps not entirely consistent, objections: first, he thinks that type-facts are not "fixed" (he raises this a half-dozen times throughout the paper); and second, he thinks some of the textual evidence that type-facts figure in the explanation of moral beliefs and actions only supports the claim that they figure in the explanation of the beliefs of "philosophers."
The tension in Alfano's criticism arises from the fact that if a "type-fact" (a psycho-physical fact about a person) does figure in the explanation of belief and action, then something must be "fixed" about it, i.e., whatever it is that makes it the type that it is. (Types can't be types, after all, unless there is something that always makes it the case that some token is an instance of its kind.) In the end (see above), he is explicit that type-facts are explanatory, and even in his second criticism, he seems to allow that type-facts are explanatory of the beliefs of philosophers, so it seems like he must agree that some kind of fixedness is key.
What I think Alfano's critique brings out is that there is an important ambiguity in talk of "fixed psycho-physical constitution." Alfano seems to take "fixed" to mean atemporally fixed, since he contrasts it most often with "mutable,"and his examples of "mutability" seem to be temporally sensitive. He is right to call attention to this, as has Janaway.
But think for a moment of Freud, whom Nietzsche influenced and who also holds a Doctrine of Types in my (and I think Alfano's) sense. Freud believed persons had a fixed psycho-physical constitution: putting aside Thanatos, every human being, on Freud's view, has a fundamental drive for oral, anal, and genital pleasure. These drives are, on the Freudian story, obviously fixed in one sense: we are supposed to be born with them, and they remain with us throughout our lives. But they are highly mutable, that is, the psychodynamic story of any person's development is the story of how these drives are repressed, modified, and sublimated. The sense in which Freud holds a Doctrine of Types--as I take it every interpretation of his thought acknowledges he does--clearly can not be a sense which rules out dramatic mutability. As Alfano puts it regarding Nietzsche (though thinking, wrongly, that I am disagreeing): "Drives survive, swell, and abate depending on their 'nutriment'" (3), a point I emphasize in NOM.
On the second point (my textual evidence and "philosophers"): Alfano quite fairly points out that some of the passages in support of the Doctrine of Types that I discuss in NOM (Alfano doesn't discuss them all) are primarily about "philosophers": this is true of GS P:2; BGE 6; and BGE 187. Since Alfano thinks the Doctrine of Types applies in these cases, he needs to explain why they do not apply more generally. Alfano ends up admitting that there are two other passages in which Nietzsche, in fact, deploys the Doctrine of Types to explain the beliefs and actions of non-philosophers, but says this is "pretty weak evidence" (11). That is a pretty feeble response! Two passages from the published corpus that Alfano discusses (and other passages from the Nachlass that he doesn't mention, but that I cite, since they are of a piece with the published work) support the broader Doctrine of Types, and Alfano simply dismisses the evidence!
But the dialectical strategy is more problematic than that. Alfano owes us an explanation of why Nietzsche would think philosophers are different in kind from the rest of humanity, such that the explanation of their beliefs and action would be different--and different in a surprising way, i.e., that the beliefs and actions of philosophers are explicable by the Doctrine of Types, but the beliefs and actions of ordinary 'herd animals' are not. Alfano has no explanation, unsurprisingly.
He also breezes by a crucial passage (GM III:7), in which Nietzsche proposes that "[e]very animal--therefore la bête philosophe too" aims for a maximum feeling of power. Here Nietzsche quite explicitly treats philosophers as instances of the human kind, which should hardly be surprising for a naturalist like Nietzsche. Is there any evidence that Nietzsche thinks philosophers are different in kind from the rest of humanity? I'm not aware of any, and Alfano cites none. (Alfano quite correctly objects  that calling the desire for a maximum feeling of power a 'type-fact' is not illuminating, though I would put the point differently than he does: it is a characteristic of the human type, but it does not illuminate the difference between human beings (the latter being Alfano's correct point.)
In conclusion, a few points about textual interpretation:
(1) Alfano claims that in GS:2, the claim about the Doctrine of Types is specific to "persons," which is an "honorific category" which rules out "those who fail to integrate, harmonize, or at least wall off their drives from one another" (5). GS 2 by itself obviously does not support that interpretation: one would need evidence that Nietzsche uses the term "Person" in this way.
(2) Alfano claims that the notion of "necessity" in GM P:2 is that of "normative necessity" (namely "what would be fitting, worthy, or appropriate depends on one's psycho-physical type" ). I do not see the grounds for that in the German, which reads:
Vielmehr mit der Nothwendigkeit, mit der ein Baum seine Früchte trägt, wachsen aus uns unsre Gedanken, unsre Werthe, unsre Ja’s und Nein’s und Wenn’s und Ob’s — verwandt und bezüglich allesamt unter einander und Zeugnisse Eines Willens, Einer Gesundheit, Eines Erdreichs, Einer Sonne.Trees do not yield fruit in accord with a "normative" necessity. (Alfano makes the same claim again at p. 10 in his MS, with respect to Twilight, "The Four Great Errors," section 2, but again the German does not support that reading.)
(3) Alfano makes a hash of the discussion of Cornaro in the "Four Great Errors" section of Twilight. He claims:
[T]he physiological facts [about metabolism] are not determinative. Nietzsche emphatically does not claim that Cornaro ate little because and only because his metabolism was slow. Indeed, he even suggests that, at times, Cornaro ate a great deal. How else can we make sense of the assertion that "he got sick when he ate more?" So, as before, type-facts do not determine behavior. (9)This gloss contradicts the passage Alfano quotes (9), where Nietzsche says that Cornaro "was not free to eat either a little or a lot, his frugality was not 'freely willed': he got sick when he ate more." In other words, a type-fact about Cornaro, namely his slow metabolism, explains why he always returned to a slender diet, namely, because he was made sick by trying to eat anything else.
I should say I particularly liked Alfano's gloss on the "enchanting abundance of types" (12) with which Nietzsche is concerned:
There are higher and lower men. There are slaves, nobles, and priests. Philosophers are often discussed as a type, as are free spirits, free thinkers, and good Europeans. There is of course the overman [sic], and his blinking counterpart, the last man. Nietzsche also discusses poets as a type, as well as saints and nihilists. The fourth book of Zarathustra is a veritable menagerie of types: the king, the leech, the magician, the retired pope, the ugliest human, the voluntary beggar and the shadow. (12)As with everyone I bother to critique at any length on this blog, Alfano is worth reading, and not only on this topic. But he has certainly helped me see some important ambiguities in my initial formulation of the Doctrine of Types that require clarification.