 The distinction presupposes that things we perceive by our senses are mind-independent material objects, or substances, which possess qualities and quantities, have relations, and take part in events. Bases for the distinction come from the age-old attempt to learn what there is in the natural world, manage it for our purposes, and attain theoretical explanatory knowledge about it. They are located in the material and structural aspects of the universe, the psychology of sense perception, and their intersection. John Locke’s famous distinction has notably different variants in the seventeenth century and all of them are disputed. Other versions are advanced and debated through the eighteenth century. Although the distinction ceases to be of much interest during the heyday of idealism, it attracts attention during the mid to late twentieth century. More recently, questions about color that can be traced to the seventeenth century have come to the fore. (See M. Wilson 1992 on the early modern inheritance of twentieth century debates. See also the entries on  color,  auditory perception, and  touch.)