I agree that there isn't always a straightforward distinction between sociology and metaphysics in Latour's work. However, that isn't really the important point. What is obvious from Latour's self-evidently sociological writings (e.g. Reassembling the Social, Paris: Invisible City, etc.) is that 'the social' is a very narrow, particular portion of the world. Latour constantly refers to how isolated, specific and fragile it is -- how it needs to be constantly taken up and rewoven and how until things are tied into the social they are not themselves social. In other words, there is no 'always already' social -- the social has to be composed; and it is composed from non-social things.
P.S. Actually I’m sympathetic to both arguments, even though they seem antithetical at first. Circling Squares says plasma is a sociological concept, while Harman says it’s a metaphysical concept.
In The Prince and the Wolf Latour gave primarily a sociological and epistemological explanation:
So plasma is what appears once the so-called natural sciences are added to the pot, so to speak, and made to circulate, not to cover the whole. (…) So, what people don’t understand is that when you do science studies you have completely different views of all that. The whole space is actually empty. And then in this very, very empty space where ignorance is the rule basically, you have circulating in the full vein, the very, very, very full vein, which is the circulation of active and formatted knowledge about mathematics, and about chemistry, and about physics, and about sociology, and about economics. So it is a reversal of background and foreground. Plasma is what you do when, to your shock, you make all of the formatted knowledge circulate inside the landscape. (p. 81)
Now, how do you call what is not formatted plasma? I mean, you can abandon the word if you want. But I think that’s the point with our criticisms: we are never in awe of or in dispute with the natural sciences. We like them because they occupy so little space! And when you’re struck by the ecological crisis, immediately you recognize a completely different territory. Here we know barely anything; we are in a state of complete ignorance. And then you have this very, very small channel of knowledge in the middle of a completely empty space. So suddenly you breathe (lots of space!) but then you are terrified by our shared ignorance, and then the question of reassembling the collective becomes central. (p. 82)
So if you take an organization (I’m very obsessed by the question of organization now). No organization would work one minute if it were not constantly drawing on this reserve of… so-called unformatted plasma. The point is just that we don’t know what it is exactly, of course. (p. 83)
So, plasma is completely… I mean it is a concept. If you want to show where the plasma is, I say everywhere
because it is… it’s not the unformatted that’s the difficulty here. It’s what is in between the formatting. Maybe this is not a very good metaphor. But it’s a very, very different landscape, once the background and foreground have been reversed and the sciences have been added to the landscape, instead of being what defined the landscape. (p. 84)
So this passage would seem to support Circling Squares’ argument. However, in Reassembling the Social, just after he first mentions “the strange figure of the ‘plasma’” (p. 50), Latour goes on to say
Most social scientists would adamantly resist the idea that they have to indulge in metaphysics to define the social. But such an attitude means nothing more than sticking to one metaphysics, usually a very poor one…” (p. 51).
He constantly argues for sociology to practice metaphysics and praises Tarde for doing so: “What is most useful for ANT is that Tarde does not make the social science break away from philosophy or even metaphysics” (p. 15). Harman therefore is also right to consider the concept of plasma within the metaphysics that Latour puts forward.
So is plasma a sociological or a metaphysical concept? I would say it’s both. This however doesn’t necessarily have to mean that it does work as such. Remember that Latour advocates the use of ‘weak terms’ as infra-language. So a concept like plasma is kind of a probe: it is sent forth as part of an experiment, the result of which can be either success or failure (and probably there is some zombie state in-between the two). My guess is that Latour probably wanted to use the concept as both sociological and metaphysical, but it is designed in such a way that if it fails as one (e.g. as a metaphysical concept when put under scrutiny by a philosopher like Harman), it can still carry on as a sociological concept. (After all Latour did say that “Maybe this is not a very good metaphor. ” ) I heard some people criticise this strategy as flip-flopping or being slippery, but it is consistent with Latour’s pragmatist commitments.
I believe that these sentiments are so commonplace in Latour's work that citations would be superfluous; however, the following posts contain more detail if such is needed:
Never does the social seem to be all encompassing -- far from it. In fact, Latour is at pains, particularly in Paris: Invisible City to show over and over again just how disconnected most of 'Paris' is. Indeed, Paris as a totality is seen to be profoundly fragile and totally dependent upon its sociality. 'Social' describes the filaments that hold Paris together qua a city -- it doesn't describe the elements that hold it together in any other sense; it doesn't describe the bonds holding together the atoms composing a street lamp on the Champs-Élysées. Or, rather, it doesn't so long as there isn't some institution socialising those bonds and tying them into the social somehow. If these bonds were social in the absence of any such institution then the social would be always already there, any- and everywhere that there were relations of any kind; it would require no composition and politics (as the progressive composition of the common world) would be pointless.
And politics is the point: take a look at Latour's recent essay 'Paris, invisible city: The plasma' -- the essay that my original post was actually commenting on. In that essay (particularly the last few paragraphs) Latour is quite explicit that the importance of plasma is political -- that if things are not always already bound up into a given social configuration then politics becomes necessary to compose and bring together those previously unsocialised elements to make a new common world. Never is it implied that these 'extra-social' elements are plasma in the sense that Harman suggests -- that of ephemeral phantoms transcending all relationality. The plasma is only implied to be those elements that are not yet circulating in social networks.
If the police chief turns off his CCTV cameras he's closed off part of the social. The streets he was previously looking at haven't evaporated -- they still enjoy other kinds of relations and other kinds of existence, he's just temporarily disconnected them from his portion of the social network of Paris. If a person dies from an unknown illness the pathogen is perfectly real but it is not social since it cannot be formatted in such a way as to circulate in social networks. And so on. (See the second post listed above for more on this.)
The main point is simply this: if you take social association to be a synonym for every kind of relation altogether (i.e. take it to be metaphysical in and of itself) rather than taking it to denote a particular kind of relation then Latour's entire sociology takes on a completely different meaning. The social ceases to be narrow, particular and requiring composition and it becomes sprawling, all encompassing and limitless. Its outside (its plasma) ceases to be other assemblages of unsocialised things enjoying and employing other kinds of relationality and instead becomes something phantosmagorical, ephemeral and occult, transcending all relation.
This little, seemingly innocent abstraction -- from social qua kind of relation to social qua all relation -- changes the meaning of pretty much everything.
Of course people are free to interpret Latour's work as they see fit and it does make a very interesting metaphysics if you abstract it from the particularities. However, what I am trying to resist is the idea that Latour's sociology can be easily abstracted from all the particularities it explicitly presupposes and lose nothing in translation.
While I very much like his version, Harman's Latour is very different to the Latour one encounters actually reading the primary texts. The translation of Latour's sociology into a metaphysics involves a large degree of transformation -- transformation that isn't always adequately acknowledged. There's nothing wrong with transformation but, unacknowledged, it will, I fear, prove misleading and confusing, conflating, as it does, quite different sets of ideas.