The Inner Ring
A subject on which Lewis has composed an entire essay, the "Inner Ring" has a significant presence in the plot of That Hideous Strength. It is a vague solidarity belonging to those inside this ring of status, excluding all outsiders. Mark, being an insecure sociologist, is obsessed with discovering and integrating himself into one of these inner rings, whether it be at Bracton College or higher up in the N.I.C.E. He notices, idolizes, and then dismisses several of these rings when greater ones present themselves, such as Curry's ring, then Feverstone's ring, then that of the N.I.C.E. When he finally has the opportunity to join the highest inner ring, that of the leadership of the N.I.C.E. ("headed" by Alcasan), however, he discovers that it isn't desirable after all, and the inner ring is empty and vain.
Progress vs Tradition
Lewis takes an unusual stance for a science fiction writer on the matter of progress; he seems to be firmly against scientific and material progress when it involves breaking away from traditional morality and values. This novel echoes the fears Lewis expresses in The Abolition of Man; when scientific progress advances far enough, humanity will destroy itself by taking away the things that make it human. This fear is embodied in the resurrected and disembodied head of Alcasan, which leads the N.I.C.E. in its attempts to take over and transform the world.
Sanctification
The main religious message here is that of sanctification; instead of merely forgiving the sins of all the evildoers (with the exception of Mark and Jane), as some Christian writers might do, Lewis makes a stronger statement. The N.I.C.E. is too far gone, so he has it destroyed with fire and brimstone, demonstrating the process of sanctification by burning out all that is wrong with the world. By being destroyed, Edgestow becomes clean again. Sanctification is not a comfortable process, and it requires suffering to create beauty and holiness.
Good and Evil
Like many of Lewis's novels, the distinction between the organizations of good and evil is sharp and clear, even exaggerated to further his point. The N.I.C.E. is clearly the enemy here; with a purely amoral and almost Satanic worldview, they intend to amass ultimate power and take over the world with the ideals of scientific progress. Their opposition is the party of St. Anne's, led by the distinguished and Christlike Dr. Elwin Ransom. In contrast to the dark and monochromatic N.I.C.E., St. Anne's seems to radiate with color, hope, and love. The forces of light and darkness thus do battle, resulting in the victory of the former through the purging of the latter.
