Jacobean - Jacobin - Jacobite

These three words all start the same, because they all derive from the Latin form (Jacobus) of the name James. (The adjective Jamesian is applied to people whose surname is 'James', usually the American philosopher and psychologist William James (1842-1910) or his younger brother, the novelist Henry James (1843-1916), naturalized British in 1915.) The spellchecker can encourage confusion between the words starting with Jacob-. Such confusion is not uncommon, but a solecism in academic writing, because their meanings are quite distinct. The different meanings are as follows:

• Jacobean is an adjective used to describe a period of UK history, and various styles associated with it (e.g. Jacobean architecture, furniture and writing). This is the period of the King James who first united the kingdoms of England and Scotland, in 1603 when he inherited the English throne from his cousin Elizabeth I. He is most properly numbered as James VI and I, as he first inherited the throne of Scotland (in 1567), where he was the sixth James to be King; and only later became the first king of England to be called James. He is most usually called James I, as that is easier - and England is the larger, and more important partner, in the United Kingdom.
• His grandson King James II (more properly 'James VII and II'), who inherited the throne in 1685, and was deposed in the 'Glorious Revolution' of 1688, left a son called James Francis Edward. As the Stuarts lost the throne in 1688, his son Prince James became their leader after his father's death in 1701. His supporters thought of him as 'James VIII and III' - a name never recognized by the government; his opponents called him 'the Old Pretender'. The supporters of the Stuarts made two great risings (in their terms) or rebellions (to the Hanoverian kings in London), the first in 1715 under James himself, the second in 1745 under his son Charles Edward - 'Bonnie Prince Charlie' or the Young Pretender. Supporters of the exiled James II, the Old Pretender, and even of the Young Pretender were called Jacobites by the new Hanoverian kings.

So Jacobean is a term to describe a period of British history; Jacobite is a term to name a particular political grouping in British history. Both come from the name of a (British) King James.

• Jacobite has a quite different reference in the context of ecclesiastical history, where the Syrian Orthodox Church is sometimes known as the Jacobite Church, probably so called after the monk Jacob Baradaeus (c500-578 CE), who was largely responsible for its foundation. The Syrian Orthodox Church is committed to the heretical doctrine of Monophysitism, which is sometimes known as the Jacobite Heresy.

• Jacobin is different. It is a name for another political party, this time not an English one. This name comes from the ordinary French form of James, 'Jacques' (see also Jacques, for a note on its pronunciation). It was a term current in the French Revolution (1789) to label a particular political grouping or party. These were the extreme revolutionaries who used to meet in the Dominican Friary. The Dominicans had earlier been nick-named 'Jacobins', because their first establishment was at a church dedicated to St James (Sanctus Jacobus, in Latin; or Saint Jacques in French.) When the extremists took over the building, the nickname came too.

[It also appears that a generalised nickname for the peasant class in France, in rather earlier history, was Jacques Bonhomme - 'Good man James'. This name in turn became a label for a bloody and violent rising of the French peasantry in 1358, the (or la) Jacquerie. (Harvey, 1946)]

All three of these words have extended meanings. Jacobin has come to mean not only 'A sympathizer with the principles of the Jacobins of the French Revolution'; but generally 'an extreme radical in politics or social organization. About 1800, a nickname for any political reformer' (OED). Nowadays, Jacobin implies 'violent' reformer. Jacobean is sometimes applied to other people called James - for example, admirers of the American novelist Henry James (1843-1916) are sometimes called, half jokingly, Jacobeans. Unless you know precisely what you are doing, in the subject area in which you are writing, only use these words in the senses given above. (There is an academic joke about the three periods in stylistic development of Henry James's writing - "James the First, James the Second, and The Old Pretender.")

In mathematics, there is a term Jacobian, after the German mathematician Carl Jacobi.