Full Idea
The fundamental role of metaphor is to project inference patterns from the source domain to the target domain. Much of our reasoning is therefore metaphorical.
Gist of Idea
Metaphors project inference patterns, so much reasoning is metaphorical
Source
G Lakoff / M Johnson (Philosophy in the Flesh [1999], 08)
A Reaction
'Project' presumably means an inference in one domain is thereby legitimate in the other, which seems dubious. In 'Juliet is the sun' how could that be true? It is better to talk of 'understandings' than of 'inferences'. We understand Romeo better.
Book Reference
Lakoff,G/Johnson,M: 'Philosophy in the Flesh' [Basic Books 1999], p.128