The greatest achievement of Reid's theory of perception is not the refutation of Hume's argument (cf. Chapter 3), but the distinction between sensation and perception. This distinction is closely connected with the distinction between act and object. For Reid defines sensation in terms of act and object as follows: 'Sensation is ... an act of mind, which may be distinguished from all others by this, that it hath no object distinct from the act itself (EIPMI 1; 27).