Scots: an outline history
The first speakers of the Old English ancestor of Scots arrived in what is now southern Scotland in the sixth century CE. These people were descendants of Germanic invaders who had arrived in the south-east of what is now England from the early fifth century. Their variety of Old English is known as Old Northumbrian, a northern sub-dialect of Old Anglian, the Old English dialect spoken over a wide territory stretching from the English Midlands to the Scottish Lowlands. The area that these first Old English speakers occupied, in what was later to become Scotland, is characterised by place-names with early Old English elements. This area consists of a wide swathe of what is now south-eastern and southern Scotland, with less extensive settlements along the Solway and, perhaps rather later, in Kyle in mid-Ayrshire.
Early predominance of Gaelic
Before the twelfth century the English-speaking part of Scotland was limited to these south-eastern and southern areas (except perhaps for the royal court of King Malcolm III and his queen, Margaret, a princess of the ancient royal house of Wessex, whom he married about 1070). By contrast, there is good chronicle and place-name evidence that by the tenth and eleventh centuries the Gaelic language was socially dominant throughout much of Scotland, including the English-speaking south-east. In origin Gaelic was the native language of the Scots of Alba, the kingdom centred north of the Forth and Clyde, whose kings in the tenth and eleventh centuries also gained dominion of the more southerly parts of what was to become an expanded Scottish kingdom.
The family tree of Scots
Until the late eleventh century the increasing linguistic dominance of Scotland by Gaelic continued, but this trend was reversed with the accession of the Normanized kings of Scotland, particularly King David I (1124–53) and his immediate successors. Thereafter place-names and other indications show a spread of the English-speaking area beyond the south-east, first to other parts of southern Scotland, then in the late twelfth and thirteenth centuries to eastern Scotland north of the Forth.
The spread of Pre-Scots
This expansion of English in Scotland was brought about by several important groups of immigrants who came to Scotland at the invitation of the king: English-speaking servants and retainers of the new Anglo-Norman and Flemish landowners, and of the monks from England and France; and English-speaking ‘pioneer burgesses’, chiefly from south-east Scotland and from northern England, who settled in the new royal and baronial burghs of Scotland that the king and his supporters had founded.
Influence of Old Norse
Though the language of the royal court and the baronage of Scotland was now Norman French, later to become Anglo-Norman, the native tongue of many of these immigrants of lesser rank was a variety of Northern English heavily influenced in pronunciation, vocabulary and grammar by the Old Norse language brought to northern and midland England by Viking-era invaders and settlers. This Norse-influenced Northern English was the principal, though probably not the only, language of the early Scottish burghs, and its contribution to the formation of the language later known as Scots is probably even greater than that of the original Old Northumbrian spoken in south-eastern and southern Scotland.
Emergence of Scots
Gradually the variety of Northern English spoken in Scotland began to diverge from the Northern English spoken in England, and the Scots language (although it wasn’t yet called Scots) emerged from the thirteenth century onwards: Older Scots, subdivided into Early Scots (up to around 1450) and Middle Scots (from around 1450 to around 1700), and Modern Scots (from around 1700 to the present day). This categorisation may be compared with the usual periods distinguished for English: Old English or Anglo-Saxon (up to around 1100), Middle English (from around 1100 to around 1500), Early Modern English (from around 1500 to around 1700) and Late Modern English (from around 1700 to the present day).
Smith, Jeremy. (2017) Scots: an outline history. Online https://dsl.ac.uk/about-scots/an-outline-history-of-scots/origins/