The most important exception from this viewpoint was that of Descartes.Although he rejected atomism, he did agree that bodies only really possess primary qualities.Although none of the major seventeenth century philosophers were sceptics, this new philosophy, having no convincing refutation of scepticism, encouraged it amongst its readers.
By adopting the term 'idea' for all mental objects Locke declared his intent to assimilate the intellectual and the sensory to each other, and to make the sensory the model for both.
If we accept that we are directly aware of ideas in the mind and not of external things, it becomes pressing to prove that there are really any external things at all.
Atomists believed that bodies are made from minute particles.
Further, they believed that the particles and the bodies made from them, possess primary and not secondary properties.
Berkeley therefore, rather than abandon direct realism, chose to modify the principle of the mind-dependence of the physical world.
According to Berkeley, the mind independence of objects is not absolute, but relative.
Descartes, in an attempt to highlight the possibility that there may be no external world, suggested that our experience might be the product of an evil demon whose intent was to deceive us.
In an attempt to refute such sceptical possibilities Descartes tried to prove, a priori, the existence of a good God.
The combination of Atomism and Newton's mechanistic and thus deterministic view of the world created major difficulties in understanding how it was possible for immaterial spirits such as God or the soul, to be related to the physical world.
The principal difficulty was in understanding how a material and immaterial substance could causally interact.