Fourth Level

A fourth level metaphor expresses as words neither its literal term nor its figurative term. If we say, "Here it comes chugging into its sty" we have very deep levels of language working here.

The word "chugging" implies a train, and the word "sty" implies a pig.

Thus

A = B

or

It (pig) = chugging (train)

When fourth level metaphors appear in poetry, they sometimes leave readers scratching their heads trying to figure out what the poet is talking about, but once readers are sensitized to such metaphors, they actually enjoy finding fourth level metaphors used in poetry. Emily Dickinson was fond of fourth level metaphors and used them in poems like "It sifts from leaden sieves."