One of Gottlieb’s central insights is that, as he wrote in his previous volume, “The Dream of Reason,” which covered thought from the Greeks to the Renaissance, “the history of philosophy is more the history of a sharply inquisitive cast of mind than the history of a sharply defined discipline.” You might say that philosophy is what we call thought in its first, molten state, before it has had a chance to solidify into a scientific discipline, like psychology or cosmology. When scientists ask how people think or how the universe was created, they are addressing the same questions posed by philosophy hundreds or even thousands of years earlier. This is why, Gottlieb observes, people complain that philosophy never seems to be making progress: “Any corner of it that comes generally to be regarded as useful soon ceases to be called philosophy.”