Lakoff thinks of Metaphorical Reasoning using a – what else? – metaphor. It’s a mathematical metaphor that treats Love is a Journey as a mapping between a subset of a Target domain (Love) and a subset of a Source domain (physical journeys).
Mapping between source and target domains
As a believer in the Logjam Metaphor for Concepts, I find that altogether too tidy. Kludge Theory of Metaphor