Foster-Harris's theories about writing were rooted in Aristotelian philosophy, and his book elucidates those theories and provides practical instruction in clear thinking and clear prose.
This book is both a sleeper and also an important book for explaining the craft of writing fiction. I say it is a sleeper because it is easy to dismiss because of the chatty conservative religious voice that it has due to its 1944 origin.
The meat of the book is a metaphor the author uses
If you are studying the craft of writing fiction then "The Basic Formulas of Fiction" does provide a major piece of the craft.