(1711-1776) Scottish empiricist philosopher; criticized rational proofs for existence of God; denied miracles. Wrote An Enquiry Concerning the Human Understanding . Regarding his theory of knowledge: all knowledge derives
from perceptions . Perceptions consist in 1. impressions (original experiences); 2. ideas (copies or memories of impressions). Impressions are 1. prior to and more
lively than ideas; 2. sensations of external sense data (i.e., color, etc.); 3. reflections on internal feelings (i.e., emotions); 4. copied by memory or imagination to form
simple ideas. Simple ideas combine to form complex ideas according to the laws of association of ideas: law of resemblance (similar ideas associate); law of contiguity
(ideas together in space or time associate); law of causality (the constant conjunction or sequence of ideas suggests causal association). Valid knowledge
consists in ideas reducible to specific impressions. Ideas like causality, substance, the self, and God cannot be reduced to impressions, hence are convenient
grammatical fictions. We cannot know an external world. "As no beings are ever present to the mind but perceptions , we can never observe a relation of cause and
effect between perceptions and objects."