This term, meaning a type of metamorphosis, is yet another one coined by Shakespeare. It is from Ariel’s song in The Tempest (I,ii):
Full fathom five thy father lies;
Of his bones are coral made:
Those pearls that were his eyes;
Nothing of him that doth fade,
But doth suffer a sea-change
Into something rich and strange.
Quite literally, the sea had metamorphosed the corpse of Ferdinand’s father into something else. Shakespeare quite literally meant simply a change wrought by the sea, but starting in the 20th century, usage came to focus on the extent of the metamorphosis rather than the agent of the change. Early metaphorical use was done in allusion to Shakespeare, as in this line from Ezra Pound’s 1917 collection Lustra:
Full many a fathomed sea-change in the eyes That sought with him the salt sea victories.
By mid-century, the term was being used without direct allusion. From Albert C. Baugh’s 1948 A Literary History of England:
An interesting paper suggesting that romance is transplanted epic, which has undergone a kind of sea-change in the passage.
(Source: Oxford English Dictionary, 2nd Edition)
Copyright 1997-2013, by David Wilton