According to Plato's Timaeus, time is the motion of light

What is it about?

This chapter is about the movement of sunlight and the concept of time in Timaeus’ cosmology in Plato’s Timaeus. It argues for three connected theses: (i) that light is a grounding principle of his account; (ii) that Timaeus puts forward a proposal for the calculation of a cosmic calendar, i.e., the counting of time according to the movement of sunlight throughout the whole world; and (iii) that he understands time (chronos) as the movement of all heavenly bodies relative to the motion of light streaming from the sun.

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Photo by Javier Miranda on Unsplash

Photo by Javier Miranda on Unsplash

Why is it important?

This chapter argues that the Timaeus’ cosmology is grounded on the visibility of the world; one of its axioms is the presence of a continuous and mobile body of light in the world originated from the Sun. It shows how this concept of visibility allows Plato to distinguish cosmic night- and- days as temporary positions relative to the Sun. This imports some refinement to his concept of day: he is aware that neither a solar nor a sidereal day would work as the unit for the calendar he would like to build, for they are all place-dependent. A calendar that would allow us to know the position of all the heavenly bodies must take this intrinsic feature of our observation into account.

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