 Traditionally, empiricists have argued that all concepts derive from sensations. Concepts were understood to be formed from copies of sensory representations and assembled in accordance with a set of general-purpose learning rules, e.g., Hume’s principles of association (Hume 1739/1978). On this view, the content of any concept must be analyzable in terms of its perceptual basis. Any purported concept that fails this test embodies a confusion. Thus David Hume ends his Enquiry with the famous remark: