The first of four Relatively Adequate Hypotheses in World Hypotheses: A Study in Evidence (1942), _Chapter VII: Formism_, has the root metaphor of _similarity_. This is a common sense approach that dates back to ancient Greek philosophy.
_Formism_ can be compared to other Relatively Adequate Hypotheses in Root Metaphor, Categories, Theory of Truth.
This chapter provides a lead-in to _Chapter IX: Mechanism_, that provides a challenge to formism where temporal and spatial structure (e.g. with gravitation and inertia). The lack of determinateness iw a weakness with formism.