Not a sentence but a formula. The Greek has no main verb: Σφαῖρα TERMψυχῆς MOTIFαὐτοειδής — "a sphere of soul, true to its own form," and then a single ὅταν-clause. It is a nominal definition, like an entry in a notebook, not an argument. Αὐτοειδής means "having its own shape," that is, not having taken its shape from something else: the sphere is a sphere precisely in being undeformed.

Four corruptions, not one. The condition is given by four negations, each a distinct deformation: ἐκτείνηται ἐπί τι ("is stretched toward something" — the desire that draws the soul outward); ἔσω συντρέχῃ ("runs together inward" — the contraction of fear or dejection); σπειρᾶται ("is spread out, scattered"); συνιζάνῃ ("settles, collapses"). The first two are opposite vices, the second two the loss of collectedness and the loss of support. A sphere can be spoilt in more than one way.

Light in place of action. The one positive predicate is φωτὶ λάμπηται, "is lit with light." The sphere does nothing: it shines, and thereby sees. Cf. 8.57, where the mind is a ray (τάσις) that neither forces through nor collapses but stands and illuminates; here the two images are joined — the figure of the sphere gives invulnerability, the light gives knowledge.

Two truths in one look. τὴν ἀλήθειαν … τὴν πάντων καὶ τὴν ἐν αὑτῇ — "the truth of all things and the truth within itself." One faculty sees both the world and itself; it is the same property with which the book opens (11.1: ἑαυτὴν ὁρᾷ). Here it is given not as an item in a list but as an optics.

Why the image is Empedoclean. The Σφαῖρος of Empedocles is the perfect spherical state of the cosmos under the rule of Love. Marcus transfers the figure from the cosmos to the soul and makes it the norm of an inward condition: whole, neither stretched out nor pressed in. Cf. 8.41, where the same sphere is called untouchable by impediments. The governing discipline is assent, the sustaining one desire.