 Leibniz, Hume, Reid, Brentano, and James held a variety of positions on unity. Briefly, for Leibniz (see the entry on  Leibniz’s philosophy of mind)  unified consciousness and the noncompositeness, the indivisibility that he took to be required for it seem to have served as his model of a monad, the building block of all reality. With Hume (1739), things are more complicated. It should have followed from his atomism that there is no unified consciousness, just “a bundle of different perceptions” ([1739] 1962: 252). Yet, in a famous appendix, he says that there is something he cannot render consistent with his atomism (p. 636). He never tells us what it is but it may have been that consciousness strongly appears to be more than a bundle of independent ‘perceptions’. Reid (1785), almost an exact contemporary of Kant’s, made extensive use of the unity of consciousness, among other things to run Descartes’ argument from unity to indivisibility the other way around. Brentano (1874) argued that all the conscious states of a person at a time will and perhaps must be unified with one another. (He combined this view with another strong thesis, that all mental states are conscious.) Finally, late in the 19th century James developed a detailed treatment of synchronic (or ‘at a time’) unity of consciousness. We will discuss his view later (see also entries on  David Hume,  Thomas Reid,  Franz Brentano,  and  William James).  