I'm glad Greenberg addressed this. Modernism and enlightenment are at time intersecting or start to appear enmeshed. Yet, modernism differentiates itself, in that we are not spectating modernism to become enlightened, but by the act of modernism itself we are in the process of enlightenment.
Enlightenment is "inward" or connection with oneself, while modernism is "outward" (human to human connection) and the art and philosophy of modernism ignites a inward outward transcendance, that directs our thoughts to a higher level or an "upward" (human divine connection).
My take on Modernism growing out of, and enlightenment as going inward, is relatable to the theories of inward outward on a micro and macro level. I will link the essay that explains the theory of inward/outward. It says, "Another metaphorical use of inside - outside is apparent when we see someone walking along, head down, lost in thought. We too, when we are having a powerful experience, might say to a friend, "I wish I could tell you what's going on inside me!" or "Something is going on deep inside me, but I can't put it into words." Someone may say he has images running through his head or that he has images in his head that he wishes he could paint. And, if he can paint them, express them, he may feel better. He feels he has made something invisible and private, visible and public, has taken what is only inside him and made it outside." To read the full essay you can go to this link: http://www.psychological-observations.com/key-concepts/inward-outward
I found it insightful and helpful to understand to build on my theory of what Greenberg is trying to convey in his point here.