Marcus Aurelius, Meditations 8.59

The sun appears to be poured down, and in all directions indeed it is diffused, yet it is not effused. For this diffusion is extension. Accordingly its rays are called extensions, because they are extended.

But one may judge what kind of a thing a ray is, if he looks at the sun's light passing through a narrow opening into a darkened room, for it is extended in a right line, and as it were is divided when it meets with any solid body which stands in the way and intercepts the air beyond; but there the light remains fixed, and does not glide or fall off.

Such then ought to be the outpouring and diffusion of the understanding, and it should in no way be an effusion, but an extension, and it should make no violent or impetuous collision with the obstacles which are in its way; nor yet fall down, but be fixed, and enlighten that which receives it.

For a body will deprive itself of the illumination, if it does not admit it.

—Marcus Aurelius, Meditations, Book 8 (tr Long)

I once met a freshman at M.I.T. who was struggling to tell me how light was both like a wave and a particle, while at the same time being neither. To his credit, he was trying awfully hard, but he ended up falling back on a rather amusing claim. “Well, we’re the scientists, so you’re just going to have to trust us.” I’d heard that from theologians discussing the Holy Trinity all the time, so I understood completely.

The scientists may always be working on explaining exactly why it is happening, though we can all surely describe a little something about how it is happening. Light seems to move straight from its source, far faster than I can follow it, and when it comes up against an object, it will behave in all sorts of interesting ways.

The rays of light may be absorbed, or reflected, or bent, or spread about, but they continue to act upon things, to extend outward, and not simply to fall away or cease to be. The rays are not effused, Marcus Aurelius says, but diffused, in that they do not flow away like a liquid but are cast toward things and at things. Using another analogy, the rays of light stand firm and are always directed, even as they do not force themselves with violence upon things.

This can tell us something about why light is often used as an image of understanding, and why the actions of mind can be fittingly compared to illumination.

Light radiates outward from its source, coming in contact with the objects around it, acting upon them, making them clear and visible as the rays move into them, through them, around them, and off of them.

So too, mind radiates outward from its source, coming in contact with the objects around it, acting upon them, making them clear and intelligible as the thoughts move into them, through them, around them, and off of them.

As the sun is to things as visible, so mind is to things as intelligible. As light remains focused, so thought should remain focused. As a ray casts itself upon things, so understanding casts itself upon things. It acts, reacts, is diffused, and transforms, yet it does not overwhelm what it meets, or just fade into nothingness.

This is all the more fitting for the Stoic, because just as light remains directed yet adaptable to objects, mind remains directed yet adaptable to the circumstances of our lives. For a man to cast his own light is not to blind others, or to burn away what is around him, but for the brightness to show him the clear path for his own choices and actions.

Mind is diffused, not effused.

Written in 6/2008