Anti-nesting principles, in consciousness studies, are principles according to which one stream of consciousness cannot "nest" inside another. According to such principles, a conscious being cannot have conscious subparts -- at least under certain conditions -- even if it meets all other plausible structural criteria for being a conscious system. Probably the best-known anti-nesting principles are due to Hilary Putnam (1965, p. 434) and Giulio Tononi (2012, p. 297). Putnam's version is presented bare, and almost unmotivated, and has been criticized by Ned Block (1981, p. 74-76). Tononi's version is more clearly motivated within his "Integrated Information Theory" of consciousness, but still (I think) has significant shortcomings.
In this forthcoming paper in Philosophia, Francois Kammerer takes another swing at an anti-nesting principle.
Though relatively neglected, nesting issues are immensely important to consciousness studies. Intuitively or pre-theoretically, it seems very plausible that neither subparts of people nor groups of people are literally phenomenally conscious. (Unless maybe the brain as a whole is the relevant subpart.) If we want to retain this intuitive idea, then either (a.) there must be some structural feature that individuals have, which groups and subparts of individuals do not, which is plausibly necessary for consciousness, or (b.) consciousness must not nest for some other reason even in cases where human groups or subparts would have the structural features otherwise necessary for consciousness.
In "If Materialism Is True, the United States Is Probably Conscious", I argue that human groups do have all the structural features that materialists normally regard as characteristic of conscious systems. A materialist who accepts that claim but wishes nonetheless to deny that groups of people are literally phenomenally conscious might then be attracted to an anti-nesting principle.
Kammerer's principle is a bit complex. Here it is in his own words:
"Given a whole W that instantiates the functional property P, such that W’s instantiation of P is normally sufficient for W to instantiate the conscious mental state S, W does not instantiate S if W has at least one subpart that plays a role in its functional organization which fulfills at the same time the two following conditions:
(A) The performing of this role by the subpart requires (given the nature of this functional role and our theory of consciousness) that this subpart has conscious mental states (beliefs, emotions, hopes, experiences, desires, etc.) that represent W (what it is, what it does, what it should do). That is to say, this subpart has a functional property Q, Q being a sufficient condition for the subpart having the conscious mental state R (where R is a mental state representing W). (B) If such a functional role (i.e., a functional role of such a kind that it requires that the subpart performing it has conscious mental states representing W) was not performed by at least one of the subparts of W, W would no longer have the property P (or any other functional property sufficient for the having of S). In other words: if no subpart of W had R, then W would no longer have S."
Short, somewhat simplified version: If the reason a larger entity acts like it’s conscious is that it contains smaller entities within it who have conscious representations of that larger entity, then that larger entity is not in fact conscious. (I hope that's fair, and not too simple to capture Kammerer's main idea.)
Though Kammerer's anti-nesting principle avoids some of the (apparent) problems with Putnam's and Tononi's principles, and is perhaps the best-developed anti-nesting principle to date, I'm not convinced that we should embrace it.
I'm working on a formal reply (which I'll probably post a link to later), but my main thoughts are three:
First, Kammerer's principle doesn't appear to fulfill the intended(?) role of excluding group-level consciousness among actually existing humans, since it excludes group consciousness in only a limited range of cases.
Second, Kammerer's principle appears to make the existence of consciousness at the group level depend oddly on factors on the individual-person level that might have no influence on group-level functioning (such as whether an individual's thinking of herself as part of the group is emotionally motivating to her, which might vary with her mood even while her participation in the group remains the same, creating "dancing qualia" cases).
Third, it appears to be unmotivated by a general theory that would explain why satisfying or failing to satisfy (A) or (B) would be crucial to the absence or presence of group-level consciousness.
None of these three points would be news to Kammerer, so to make them stick would require more development than I'm going to give them today. But before doing that, I thought I solicit reactions from others -- either to the general issue of anti-nesting principles or to Kammerer's specific principle.
Update Jan. 26, 2016:
I have now drafted a more formal reply essay here.
Martian Rabbit Superorganisms, Yeah! (May 4, 2012)