From the comments to my previous post:
And that Spinoza class sounds awesome. Nadler is the man. Maybe you could post the Davidson/Spinoza stuff. My sense is the comparison is much richer than just saying, gee, they're both kind of saying "there's just one kind of stuff with different aspects." But I wonder what you said, and if Nadler said anything interesting back.
I do think that there's a deeper connection between Davidson and Spinoza than that. I think the most straightforward expression of this is actually in "Aristotle's Action"; Davidson is really free with his historical connections there, and praises Spinoza for his dismissal of "the will" in favor of having ideas themselves having force. (This is Spinoza's famous criticism of Descartes as imagining ideas as being like "mute pictures on a wall".) Davidson and Spinoza both have a keen sense of humanity as being a special sort of thing within nature, and not something which is added to nature from outside, as "a kingdom within a kingdom". This basic sense that "We are just bodies, though mental-talk isn't body-talk" is one thing that makes Spinoza feel special among the early moderns, and makes him relatable in a way that someone like Malebranche isn't.
My Spinoza paper's main argument was that to make sense of the argument for E2P7 as actually being something like a good argument, we had to understand Spinoza as committed to there being only one "order of things in nature", with each "connection" being both a causal connection between ideas and a causal connection between bodies (depending on how we make sense of it -- and we can only make sense of it in one of those two ways, and not just as "connected things in nature", because of Spinoza's connection of causation with knowledge in E1Ax4, which is supposed to be a sufficient proof for E2P7). Now, it's still hard to see how the argument in E2P7D is supposed to work, but if all Spinoza wants to say there is "Look, there's just the one nature with its mess of causal connections", then it can at least begin to make sense how this claim could have such slim argumentative support. Any richer notion of "psychophysical parallelism" as being what E2P7 is talking about has a serious problem trying to make sense of the idea that this follows "evidently" from "The knowledge of an effect depends on and involves the knowledge of a cause". That's just not a wide enough base to build much off of.
And if I can get that much from E2P7, then it's pretty easy to see that Spinoza is an anomalous monist: he's committed to there being no psychophysical laws (because all explanations are internal to a single attribute), he holds that all causation is backed by strict physical laws (because all things in nature are at least modes of extension, and all causation is lawlike, by E1Ax3), and he's committed to there being (in some sense) psychophysical causal relations. Which are close to the three premises from which Davidson gets to anomalous monism in "Mental Events"; at any rate they're close enough that showing their consistency leads to an interesting position.
This last premise was the part I had to argue for the most, since Spinoza seems to flatly deny it in E3P2. Davidson has some arguments for what to say about this in "Spinoza's Causal Theory of the Affects", but I found some aspects of his reading of Spinoza to be unsatisfying (because he relies on Curley's reading of "Ethics", which Nadler used as a foil for a lot of the class). Thankfully Della Rocca's work was incredibly helpful here ("Representation and the Mind-Body Problem in Spinoza" is fantastic). The key twist was to treat "a causes b" as intensional, for Spinoza. You can change its truth-value by changing how 'a' or 'b' is described. So Spinoza's explicit rejections of cross-attribute causation do not show that he has to reject an extensional notion of cross-attribute causation, which is what's at issue for Davidson's argument. And then all of the standard "psychophysical parallelism" bits in "Ethics" are pretty smoothly handled by treating Spinoza as talking about psychophysical causation while not mentioning extensional causal relations, and the general close connection of the mind and the body through "Ethics" (especially in the treatment of the affects) becomes easy to understand. (This obviously has a "principle of charity" motivation to it, too, since the complete rejection of psychophysical causal relations is pretty nuts; Spinoza's mockery of Descartes's attempts to make sense of the soul literally moving the body look a lot more sensible if he has some other way of saying how our attitudes can make us move. If Spinoza's real gripe there is that the idea of a Cartesian mind which is totally separate from the body does not make sense (and so instead we should identify the mind and the body, while understanding it in two different ways), then BS is suddenly a much more attractive character for we modern naturalists.)
Della Rocca also has a nice little argument that "things" (as in "one and the same thing expressed in two ways", E2P7S) have to be modes: all there is (for Spinoza) is substance and its modes, E1P15D; "thing" as "substance" does not make sense in the context of E2P7S, since then "the circle in nature" might as well be identified with "the idea of the Panama Canal" as with "the idea of the circle'; ergo things=modes. So modes can expressed in multiple ways (as bodies and as ideas). This was the only place where Nadler had a problem with my paper: Spinoza never talks about modes that way, as if they could have different descriptions under different attributes. And he sometimes seems to speak of the mind and the body as two modes, not one. But my answer to that was to take the same line as I did with causation: Spinoza has an intensional notion of mode-identity. The truth-value of "a is the same mode as b" depends on how 'a' and 'b' are described.
Now, one big difference between Davidson and Spinoza is on the nature of psychological understanding. Spinoza is the theorist of man as "a sort of spiritual automaton"; Davidson does not believe in psychological laws. One interesting thing that I realized during this paper is that the way Davidson introduces "anomalous monism" does not entail accepting the three principles he argues from in "Mental Events"; the position Davidson defends in that paper is just one possible form anomalous monism can take. So the three principles Spinoza accepts which I said were "similar" to Davidson's are in fact sufficiently similar to make him a genuine anomalous monist by the terms of "Mental Events".
The way Davidson divides up his four categories (nomological monism [materialism], nomological dualism [interactionism, parallelism, epiphenomenalism], anomalous dualism [Cartesian dualism], and anomalous monism) is by looking at whether one accepts or rejects psychophysical laws, and whether one identifies mental events with physical events or not. Spinoza clearly rejects psychophysical laws and identifies mental events and physical events. So Spinoza is an anomalous monist despite holding a nomological view of the mental. Which is an interesting sort of position.
One thing I didn't deal with in my paper (except very briefly) was adjudicating between Davidson and Spinoza on the topic of psychological laws. Davidson I think gets this just right: the anomalism of the mental is just the sort of freedom we should want the mind to have. I can't see the attraction Spinoza is supposed to have here; his lists of affects just felt tedious, though some of the definitions are clever, and I just don't see how the conatus argument in E3P6 is supposed to work at all. (Della Rocca and Nadler both said that the argument just doesn't work; it's a key part of the book where the argumentation is just shoddy, as with E1P6D. In fairness to Spinoza, his bad arguments are at least very clearly laid out.) This isn't even to mention the really embarrassing parts of Spinoza's psychology, like the incredibly simplistic account of memory in E2P18S. The interesting stuff in "Ethics" seems to me to largely be in the broadly naturalistic picture Spinoza offers, and in the fun Descartes-bashing and anti-religion stuff sprinkled throughout. (I think it's this last bit that Nadler got most excited about.)
I should read "Spinoza's Heresy" some day to see just how E5P23 is supposed to get dealt with; Nadler's view seems to be that the "eternal" part of the mind is just the abstract idea of its essence. Which seems to fit with the demonstration well enough, but I can't see how it fits into the book. On Nadler's reading, Spinoza just thinks that the soul is mortal and dies with the body, end of story; which makes all of the stuff about the "intellectual love of God" and "the eternity of the mind" that closes the book out very, very weird. On Nadler's reading it seems like all of the weirdness is superficial; really Spinoza is not saying anything that a materialist would have any problems with. But it feels like Spinoza has something in the background here that's going lost; that superficial weirdness is really weird, in a way that (e.g.) his doubletalk about the value of "religion" is not. The praise of religion is plausibly just Spinoza trying to win over converts to his anti-religious way of thinking; the stuff about the amor intellectus Dei doesn't seem like something that we're supposed to just slough off once we are converted to Spinozism. It's supposed to be genuinely liberating in some way; the sad passions are somehow being combated by the eternal part of the mind. This part of Spinoza is just dark to me. I don't get it.