Entry updated 30 March 2026. Tagged: Theme.
Term occasionally used in sf criticism for a crucial forking-place in Time, whose manipulation via Time Travel or alteration by sheer happenstance may radically affect the future that follows, typically spawning an Alternate History. "Jonbar hinge", "nexus point" and "point of divergence" have also been used synonymously.
The headword name derives from Jack Williamson's The Legion of Time (May-July 1938 Astounding; rev 1952), which deals with Changewar between the potential future empires of Jonbar (good) and Gyronchi (bad). The former is named for the character John Barr: the fiercely contested jonbar point is the moment when as a small boy Barr picks up either a Magnet, inspiring him to a life of science which ultimately brings Jonbar into existence, or a pebble, leading Barr to obscurity and the world to Gyronchi. In Isaac Asimov's The End of Eternity (1955), such key points are carefully calculated by watchful Time Police to achieve maximal effect from minimal interference: thus, for example, a brief delay caused by minor sabotage eliminates a Future War in the following century.
Most works of Alternate History develop their changed future from a single explicit or implied point of divergence. Notable examples include the 1588 assassination of Queen Elizabeth I and subsequent triumph of the Spanish Armada Invasion in Pavane (coll of linked stories 1968; exp rev 1969) by Keith Roberts, and the twelfth-century survival of Richard I and hence the Plantagenet dynasty (leading to a much earlier British Empire) in the back-story of the Lord Darcy sequence by Randall Garrett. The innumerable World War Two turning points whereby Hitler Wins can be simple as the successful German invasion by sea in Len Deighton's SS-GB: Nazi-Occupied Britain 1941 (1978).
There are many quasi-fictional Thought Experiments in historical extrapolation from a particular branch of divergence, such as those collected in If It had Happened Otherwise: Lapses into Imaginary History (anth 1931; vt If: or History Rewritten 1931; exp 1972) edited by J C Squire, or What Might Have Been: Imaginary History from Twelve Leading Historians (anth 2004) edited by Andrew Roberts (1963- ). A humorous take on such speculations is "If Grant Had Been Drinking at Appomattox" (6 December 1930 The New Yorker) by James Thurber. [DRL]
see also: Chrononauts.
further reading
- Brian W Aldiss. "Judgement at Jonbar" (Spring 1964 SF Horizons) [pp13-37: mag/]
- Brian W Aldiss. The Jonbar Point: Essays from SF Horizons (Reading, Berkshire: Ansible Editions, 2020) [nonfiction: coll: two studies first published in SF Horizons including the above: introduction by Christopher Priest: pb/photographic]
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