Descartes’ greatest achievement occurs in a very brief moment in Meditatin 1 when, when exploring whether we can be certain of the self and body he wonders whether he might be mad or dreaming. At that moment the subject ($) is distinguished from the self (I(a)). He discovers that the subject is void, emptiness, freedom, the possibility of self-creation.  The subject is not the self and, indeed, the self is, as Descartes suggested, a perpetual question to us.  Subject is an excess over every identity and the failure of every identity.  Subject is the slipperiness of any identity or ego.  This is where so much post-structuralist thought gets it wrong with Descartes:  it confuses subject with the ego (I(a)) or the self, missing that subject is essentially the failure of any self or ego to be what it takes itself to be.  Subject names the possibility of writing the self otherwise; the failure of every essence.  It is that which contests all essences of gender, ethnicity, nationality, embodiment, and all the rest.  It is the perpetual possibility of being otherwise and the abyss of being anything.  It is for that reason that it is right to call the subject void or emptiness.  It is here that the possibility of the anarchy lies, as well as our freedom and autonomy.