Campbell, Kirsten. Jacques Lacan and Feminist Epistemology. Florence, KY, USA: Routledge, 2004.
Lacan argues that the position of exception to the phallic signifier is not that of negation or contradiction but of indeterminacy (S20: 103).
The not all of the female subject is a position which the symbolic does not capture. As a position which the law of the signifier does not determine, the not all is a limit to its claim to represent an infinite set of all (S20: 103). It marks both the limit of the phallic signifier (as its exception) and the failure of that limit (as its infinite excess). The not all is an objection to the universal claim of the masculine (S20: 103). The not all of a female subject is a position of a non-universal subject, and so is a position of specificity and particularity. The logic of that position is ‘one by one’ (S20: 10). In the position of not all, the female subject is a specific and particular subject: women ‘do not lend themselves to generalization. Not even, I say this parenthetically, to phallocentric generalization’ (1975e: 18). For Lacan, women do not lend themselves to generalization ‘since we cannot speak of more than one’ (1974: 40). 89
De Lauretis objection which sounds alot like Butler’s
De Lauretis emphasizes the radically indeterminate and unstable nature of this subject, and for this reason rejects a Lacanian theory of the subject. She argues that it proposes ‘a subject constructed in language alone, an “I” continuously prefigured and preempted by an unchangeable symbolic order’, and so cannot address a feminist notion of the subject as ‘a multiple, shifting, and often self-contradictory identity’ (1988: 9).
However, my reformulation of the later Lacanian account of the sexed subject emphasizes its social production as an unstable subject that can therefore be engendered as political. It does not conceive the female subject as an ontological femininity, nor as founded in sexual difference.
The position of the not all is not an ontological description of women, but rather a description of the position of the female subject in socio-symbolic relations. This concept of the female subject locates women neither ‘outside’ nor ‘inside’ the socio-symbolic order. Rose points out that ‘the former relegates women outside language and history, the latter simply subordinates them to both’ (1982a: 57). Rather, resistance can be found in the faltering of the phallic function, which provides the possibility for imagining the socio-symbolic contract otherwise. This possibility is that the phallic Symbolic order does not define all (others) because it fails to know the female subject.
The not all is a position that is neither ‘inside’ nor ‘outside’ the Symbolic order but is in excess of its phallic imaginary. It represents the failure of a metaphysics of phallic identity, and in that failing lies the possibility of an epistemological shift that is able to account for, and move beyond, its limits. This strategy recognizes that 
is a masculine fantasy that does not represent women. As such, does not describe ‘women’, but is rather a site of feminist contestation. The female subject becomes a position of strategic engagement that recognizes that in ‘feminist theory one speaks as a woman, although the subject “woman” is not a monolithic essence defined once and for all, but rather a site of multiple, complex and potentially contradictory sets of experience’ (Braidotti 1992: 182). This conception of the not all of women requires understanding the female subject not as an ontological ground of the feminist subject, but as a political project which aims to ‘bring about new forms of representation and definition of the female subject’ (Braidotti 1992: 182). It thereby reveals that the possibility of the feminist knower – a knower engaging in the transformation of the failure of the phallic signifier and the socio-symbolic order which it guarantees – is contingent upon a political project of new forms of the socio-symbolic relations and subjectivity. 89-90