The procedure whereby the senses of touch, sight, smell, sound, or taste generate information about the objects touched, seen, etc. A fundamental concept of epistemology, observation has nevertheless proved hard to understand. Observations are more than the mere causal impact of external physical stimuli, since such stimuli only give rise to observations in a properly prepared and receptive mind. Nor are they well thought of in terms of atomistic ‘impressions’ (see Gestalt psychology, myth of the given, sense data). Observation seems to require the use of cognitive powers of classification and memory in tandem with the use of the senses. This is the partnership celebrated in the second half of Kant’s famous remark in the Critique of Pure Reason that ‘thoughts without content are empty, intuitions without concepts are blind’ (A51/B75). Making sense of this partnership is the basic problem of empiricism, and a central problem for any epistemology.