 4.216–1059. The basic theory is then applied to sense-perception, and above all to vision and visualization, including dreams. (The non-visual senses are addressed too, even though, technically speaking, they rely not on simulacra but either on direct contact with their object or on other kinds of effluence.) Lucretius devotes a substantial section to describing optical illusions, which his atomic theory claims to be able to account for without sacrificing its fundamental position that it is never the senses that lie, only our interpretations of their data. Indeed, he defends this latter Epicurean paradox by deploying a classic self-refutation argument against the sceptical alternative: to deny that we have access to knowledge through the senses (its only possible entry route) is a philosophical stance that disqualifies its own adherents by depriving them of any possible grounds for its assertion (4.469–521).