 The aim of the ancient sceptics was not to achieve knowledge of nature; it was to attain “tranquillity in matters of opinion” (kata doxan ataraxia) (Sextus PH 1.15). Something similar may be said about the Epicureans. Their movement can be regarded as a “secular religion” (Milton 2002: 182), which aimed to achieve a knowlege of nature only insofar as this promoted peace of mind. (For a more vigorous defence of the scientific credentials of Epicureanism, see Asmis 1984.) But even if this is true, the writings of Epicurus and his followers do embody a distinctive form of empiricism. It is, first of all, a tabula rasa empiricism, holding that the evidence of the senses is “the base and foundation” of all our knowledge (Sextus M VII 1.216). But it differs from some other forms of empiricism both in regarding as infallible the immediate deliverances of perception and allowing for the mind to be affected by external objects in ways independent of the five senses. Epicurean empiricism is also more tolerant than that of the medical writers and sceptics, since it accepts inferences to unobservable causes. It is not, in other words, an explanatory empiricism. Indeed this seems to be the reason why the more sceptical Sextus counts Epicureans among the “dogmatists” (PH 1.3).