Q: Was “middle ground” originally a nautical and/or cartographic term? It’s still used commonly by mariners and mapmakers, but outside the seagoing community it seems mostly to be used figuratively.
A: Yes, “middle ground” was originally used by sailors and mapmakers. When it appeared in the 17th century, it referred to “a shallow place such as a bank or bar, esp. as a navigational obstruction,” according to the Oxford English Dictionary.
In the earliest OED example, the term is used as a proper name: “Within them lyeth a plate on the starboard side, a little to the n. wards of the Haven, called the Middle-ground” (from A Description & Plat of the Sea-Coasts of England, 1653, a guide for sailing in English waters).
The most recent Oxford citation is from a late 19th-century description of Humboldt Bay on the north coast of California: “Their burdens of detritus find fitful equipoise on the spit terminals, on the middle ground within, or on the bar without the entrance” (Overland Monthly, October 1896).
The OED, an etymological dictionary, says the nautical sense of the term is now obsolete, but two of the ten standard dictionaries we regularly consult have entries for it.
Merriam-Webster Unabridged defines it as “a shoal in a fairway having a channel on either side,” while Dictionary.com says it’s “a length of comparatively shallow water having channels on both sides.”
As you point out, the expression “middle ground” is still used by mariners and mapmakers. For example, the online International Dictionary of Marine Aids to Navigation describes the term this way: “Island or shoal which divides a fairway into two shipping channels; these subsequently join again into a single channel.”
And a glossary of nautical terms on the website of Practical Boat Owner, a British magazine, defines it as “A shallow bank which divides a channel or fairway into two parts. It is marked with Middle-ground buoys which usually indicate the deeper of the two channels so formed.”
As for the other senses of “middle ground,” in the 18th century it came to mean the middle distance in an artistic composition. The earliest OED example describes how painters divide their compositions “into fore-ground, middle-ground, and distance or back-ground” (from The Analysis of Beauty, 1753, by the English painter William Hogarth).
The modern figurative sense of “middle ground” showed up in the early 19th century, according to Oxford citations. The dictionary defines it as “a (metaphorical) place or position halfway between extremes; an area or position of moderation or possible compromise.”
The first OED example, which we’ve expanded, is from a treatise on religious imagination:
“But when, either by the refinements of rationalism—a gross misnomer—or by superstitious corruptions, the central facts of Christianity are obscured, no middle ground remains between the apathy of formality and the extravagance of enthusiasm.” (From Natural History of Enthusiasm, 1829, by Isaac Taylor.)
The dictionary’s most recent figurative example is from the late 20th century: “With Labour’s Tony Blair seeking to steal the political middleground by talking of lower taxes … the Tories will be under pressure to match the promises” (Daily Telegraph, London, Aug. 17, 1994).