In recent years renewed interest in Thomas Reid's philosophy has led to fruitful discussion of Reid's theories of sensation and perception. Although certain aspects of these topics can be discussed without setting out Reid's version of the primary-secondary quality distinction, the ultimate evaluation of Reid's work on both sensation and perception requires discussion of his views on primary and secondary qualities. Current Reid literature virtually ignores this important topic. This paper is an attempt to remedy this situation. In addition to setting out Reid's position on primary and secondary qualities I will discuss Reid's curious relation to the New Science of his day and will explain how Reid thought he could reintroduce the primary-secondary quality distinction despite Berkeley's attacks on the doctrine.In both of his major works, An Inquiry Into The Human Mind, and Essays On The Intellectual Powers Of Man, Thomas Reid was intent upon examining the philosophical problems of human knowledge. In the Inquiry perception received his exclusive attention. In the Essays other cognitive operations were examined as well. The impetus for these investigations was provided by Reid's negative assessment of the achievements of his philosophical predecessors.