I call desolation what is entirely the opposite of what is described in the third rule, as darkness of soul, turmoil of spirit, inclination to what is low and earthly, restlessness rising from many disturbances and temptations which lead to want of faith, want of hope, want of love. The soul is wholly slothful, tepid, sad, and separated, as it were, from its Creator and Lord. For just as consolation is the opposite of desolation, so the thoughts that spring from consolation are the opposite of those that spring from desolation. Analogy is a comparison or an intuitive inference of a similarity of an actual or assumed relationship, in some way, between two things in order to go from the known to the unknown. I see it now.
Analogy is essential to human knowing because knowledge develops from the known to the unknown.
In literature, figures of speech such as metaphors, similes, allegories, parables, etc., are specific kinds of analogy. They knew how to do this even though the human race had only studied aspects of Mars through astronomy, physics, etc. By analogy with the physical laws operative on our own planet, they could recognize and extrapolate the similarities and differences of Mars from those of Earth. However, they had to assume the existence of some relationship with aspects of Earth which they already understood. To do this, they had to use an analogous way of thinking.