DOI: 10.1111/j.1468-0378.2010.00439.x Two Unities of Consciousness Elizabeth Schechter Abstract: This paper argues for a distinction between possession of a unified consciousness and possession of a single stream of consciousness. Although the distinction has widespread applic- ability in discussions of the structure of consciousness and of pathologies of conscious experience, I will illustrate its importance primarily using the debate about consciousness in split-brain subjects, suggesting that those who have argued that split-brain subjects have two streams of consciousness apiece and those who have argued that they have a unified consciousness may both be right. 1 Introduction This paper is about what it is for consciousness to be unified, and whether it might be possible for a subject to enjoy a consciousness that was unified in one important sense, but not in another. I draw a distinction between two ways of thinking about the unity of consciousness, a distinction that has not been widely recognized or sufficiently appreciated in discussions of conscious unity or of pathologies of consciousness. This is the distinction between the coherence of conscious experience on the one hand, and the co-consciousness of experiences on the other. After explaining the concepts of conscious unity that I call ‘coherence unity’ and ‘conscious singularity’, I will consider whether they might in fact pick out at least partly dissociable aspects of conscious mental life. Here is how the rest of the paper will go. Sections 2 and 3 explain the two concepts of conscious unity: conscious singularity, or possession of a single stream of consciousness, addressed in Section 2, and coherence unity, the subject of Section 3. Section 4 notes that there are bound to be conceptual connections between conscious singularity and coherence unity, as well as empirical connections between conscious states’ coherence and their co-consciousness. For this reason, one might maintain that there is only a single phenomenon picked out by these two concepts. One might, that is, maintain that a subject with a coherence unified consciousness must have a single stream of consciousness, and vice versa. So far as I know, in fact, no one has rejected both halves of this biconditional. I nonetheless present arguments for its rejection in the second part of this paper. The first half of the biconditional—which states that any subject with a single stream of consciousness must have a coherence unified consciousness—is tackled European Journal of Philosophy ]]]:]] ISSN 0966-8373 pp. 1–22 r 2010 Blackwell Publishing Ltd., 9600 Garsington Road, Oxford OX4 2DQ, UK and 350 Main Street, Malden, MA 02148, USA.