For a lifetime, the philosopher Karl R. Popper, who hails from Vienna, engaged with the pre-Socratics Parmenides, Xenophanes, Heraclitus, and others. Europe owes them the foundation of its philosophy, science, and humanism. In this unique collection of texts, it becomes clear how the founding fathers of philosophy and natural science contemplated problems. Popper demonstrates in his clear language the astonishing diversity and enduring relevance of early Greek thought. "Parmenides opened my eyes to the poetic beauty of the earth and the starry sky. He taught me to view them with a new exploratory perspective." Karl R. Popper.