In Plato's Phaedo, Simmias, speaking about the immortality of the soul, says: "I think, Socrates, as perhaps you do yourself, that it is either impossible or very difficult to acquire clear knowledge about these matters in this life. And yet he is a weakling who does not test in every way what is said about them and persevere until he is worn out by studying them on every side. For he must do one of two things; either he must learn or discover the truth about these matters, or if that is impossible, he must take whatever human doctrine is best and hardest to disprove and, embarking upon it as upon a raft, sail upon it through life in the midst of dangers, unless he can sail upon some stronger vessel, some divine revelation, and make his voyage more safely and securely."¹