Where the psychologist catalogues associations, Peirce performs a logical analysis and finds a single principle underneath them all. The law of mind is not mechanical, because it is irreversible: once an idea has spread and been generalized, the process cannot run backward, any more than a person can unlearn a language. Time itself, for Peirce, has the structure of this law.
For one idea to affect another, the two must be continuous — feeling cannot leap across an absolute gap. Peirce therefore takes continuity (synecheia) as the master conception of philosophy. Personality is a coordination of ideas living in continuity, not an instantaneous thing; it reaches into the future, which is why a person can make promises and pursue purposes.
The essay ends at a striking metaphysical destination: if mind is the primal stuff, then matter is mind whose habits have become so fixed that spontaneity has all but died out of it — “effete mind,” hidebound with habit. Physical law is thus a limiting case of the law of mind, and the old dualism of mechanism and spirit dissolves into a single story of habit-taking.
From “The Law of Mind,” The Monist, July 1892 — the central paper of Peirce’s cosmological series.