‘Puzzles about first principles’ examines the importance of Parmenides. Parmenides is important for his powerful distinction between appearance and reality. He throws at us the challenge of whether we should trust our reason or our senses, in circumstances when they seem to conflict. Parmenides did for science what Plato would later do for morality and aesthetics as well: he alerts us to the fact that opinions are just opinions, and they may differ widely. To search for knowledge is to search for access to the truth, not to collect other people's opinions, and philosophy conducts its unrelenting search for truth in the steps of Parmenides.