To today’s reader it may seem unusual that the philosopher’s first order of knowledge is number and calculation, yet that is what Socrates prescribes. On November 28, 2021 participants from the Toronto Philosophy and Calgary Philosophy Meetup groups discussed the reasons why, in our fifth session on Plato’s Republic. We continued the dialogue on the nature of time that began in episode 4, and considered the differences, uncertainties, and probabilities that exist in the changing present – the state of “coming to be” that never “is”, in contrast to the eternal being of the past and future. In the present, the philosopher is able to navigate the physical world of differences and distinguish truth from falsehood, when equipped first with knowledge of number and calculation, then plane and solid geometry, and finally astronomy. Unlike the Guardians and the prisoner in the cave whose knowledge is restricted by their teachers to the visible, the philosopher can summon reason and apply dialectic to understand invisible first principles. Is knowledge derived solely from sensory perception? How does our technology change perception, and how do we train the mind? These were among the questions raised that will help bring us to a conclusion on the nature of justice when we finish our six-part series on The Republic in two weeks.