If minds are brains, we just do not need the hypothesis that they are souls too. Dualist explanations
are inherently less simple than materialist ones, as they posit the existence of two kinds of things
rather than one. Simplicity is not a virtue all by itself, as we see in the hypothesis of the first great
philosopher-scientist, Thales, that everything is water. Einstein said that everything should be as
simple as possible but not simpler, and Thales' hypothesis is just too simple, as was Aristotle's
somewhat more complicated story that the four fundamental elements include earth, air, and fire as
well as water. Modern chemistry sees the need to consider more than a hundred elements, including
hydrogen and oxygen, which combine to produce water. Similarly, it is possible that there could be
phenomena that require explanations invoking soul or spirit in addition to matter and energy.
However, the rapidly progressing development of neuroscientific explanations of many mental
phenomena suggests that souls are no more part of our best general explanatory account than is
caloric, which was thought to be the substance of heat before the advent of the theory that heat is just
molecular motion.