The period from about 1730 to about 1800 was one of the brightest in the history of the Scottish universities (and one of the dimmest in the history of the English ones). Why this was so has never been established; it may perhaps be attributed to an influx of wealth and self‐confidence following the Treaty of Union in 1707, coupled with lack of clerical control over the universities. The main figures of the Scottish Enlightenment were Francis Hutcheson (1694–1746), Adam Ferguson (1723–1816), David Hume, Adam Smith, and Dugald Stewart (1753–1828). It is difficult to generalize about the thought of a loosely connected group of people, but the Scottish Enlightenment tried to construct first principles of politics and society free from the religious underpinnings that had previously been thought essential even by liberals such as Locke. Hume and Smith developed classical economics.
The Scottish Enlightenment had reciprocal links with France and America. Hume spent several years in France, where he wrote his Treatise of Human Nature. Smith and Turgot admired each other's work. Jefferson owed much to a Scottish teacher at William and Mary College, and much of mainstream liberal thought may have reached America through such routes. Although the Declaration of Independence sounds very Lockean, it reflects Locke inherited through the Scottish Enlightenment (and thus secularized) rather than directly.