Abstract Since the days of Democritus, Plato, and Aristotle the main concern of philosophers of mind has been whether there is an independent realm of the mental beyond the realm of the physical. This question has mainly been understood as that of whether there are independent mental substances — souls or selves. Most of what has been written in the philosophy of mind during the last seventy to eighty years, however, has instead been concerned with the question of whether there are independent or irreducible mental properties. To many it has seemed obviously true that there are no mental substances, but with properties things are different. The history of answers to questions such as ‘Is being in pain or thinking about Paris really something physical?’ (including the answers associated with logical behaviourism, the identity theory, functionalism, and supervenience theories) has been told time and again. Nonetheless, it is worth taking a new look at it.