Perhaps Heraclitus lived before Parmenides, perhaps he lived after, perhaps he lived at the same time. Whichever way, his sayings cry out to be read … - Catherine Rowett

Philosophy has come to include, for us, a wide range of theoretical questions that typically look beyond what we can answer by experimental enquiries. While science asks how matter behaves, and tests its theories with observation, philosophy asks what matter is, or how observation can teach us anything. While mathematics asks what the sum of 2 and 7 is, philosophy asks what the number 2 is, and whether 2 plus 7 could ever make anything but 9.

For Heraclitus, the logos is something that we need to learn to notice if we are to understand the true significance of the world. It manifests itself all around us but, Heraclitus suggests, only a few intelligent people ever realize what is going on.

Besides the ‘how many?’ question, Empedocles seems to be answering two other ancient questions: ‘How did the world come to be as it now is?’ and ‘How did it come to have the creatures that it now has?’. [...] His answers are subtle and intricate.