A key principle in the design of Painshill is illusion. This particularly affects spatial awareness - the lake, because it changes shape and cannot be seen all at once, has often deceived visitors as to its actual size, as has the pine forest at the western end of the gardens. The open lawns were made to seem doubly large by cleverly placed plantings, again because they could not be seen in one view. Buildings, too, could be deceptive, such as the Hermitage, which had a totally different back from its front and would be taken for another building when approached late in the circuit from the rear. Many of the buildings created illusion in being made of a different material from that which they appeared to be made from - the portico of the Temple of Bacchus and the Gothic Temple were of wood to resemble stone, and the Mausoleum, Gothic Tower and Ruined Abbey were of brick rendered to look like stone. The wooden five-arch bridge was often mistaken for stone. The grotto, again basically brick, was given a dressing of 'tufa' to look like a natural cave. Illusion could extend to an entire area.

The whole of Grotto Island was covered with 'tufa' constructions of various shapes and sizes as if to suggest an extensive outcrop of marine rock. Large boulders were strewn around the cascade to give the impression of mountainous terrain. The pine wood would suggest a forest. There is something theatrical, too, in Hamilton's design. His control of illusion nods to the perspectives of a theatre as well as of a painting, and the buildings have sometimes been compared to a theatre or even a film set. The Kentian tableau, because it is of three dimensions, owes as much to the theatre as it does to art. And the amphitheatre, though so called because of the tiered nature of the plantings, suggests by name a link with the world of the theatre. In the eighteenth century the word 'theatre' could denote a place where things happened (compare the more modern 'theatre of war') as well as the more specific meaning of a place of performance; and a good many things happened at Painshill.

The metaphor of the theatre occurred to Hamilton when describing in a letter the political turmoil of 'this theatrical winter'. Painshill may be seen as a garden with a political flavour in a broad sense of the word, inasmuch as the natural landscape look was being cultivated by the Whig Opposition, whose watchword was Liberty, expressed in gardening terms as freedom from geometrical constraints and from the authoritarian tyranny of design exemplified in Louis XIV's Versailles. As we shall see, Hamilton's work and social milieu brought him into the Opposition camp even though he himself was not politically active. There was also a moral dimension to the gardens. Stephen Duck, in the poem quoted earlier, gives implicit approval to the vineyard as a source of giving pleasure, and Hamilton's transformation of the land from infertile to productive was very much in tune with the moral tenor of the times, although self-interest was permissible at the same time: 'were this sort of Husbandry practised in many other Parts of England, it would be of great Service to the Public, and amply increase the Value of the Lands to the Proprietor'. Painshill was not created in a vacuum, and Hamilton was well aware of contemporary developments in garden layout, some of which must have rubbed off on him. Writers such as Alexander Pope had been calling for a more natural approach much earlier in the century, though the relaxation of straight lines took time to happen in practice. It was not until the 1730s that the more naturalistic look started to come in, and for some years geometry lingered on, often in conjunction with its opposite, especially in those gardens such as Stowe which had originally been constructed along bold formal lin.