 The core notion of a sense datum is an immediately given, minimal perceptual object, consisting in the case of vision of a shaped patch of color. Often, but not always, this datum was considered to be two dimensional. It typically was contrasted with the perception of a three-dimensional material object of a particular kind and displaying a panoply of further properties. In the classical period (the first several decades of the twentieth century), sense data were typically taken to be non-mental and mind-independent, and were often regarded as representing material objects. In some cases, sense data or their kin were taken to be elemental constituents in the composition or bundling of sense particulars. These particulars did not refer to material objects per se but, when conjoined, composed a perceptual world (as in Russell 1914a and 1914b). More recently, sense data have been viewed as mental items (e.g., Jackson 1977), and perhaps as leading to idealism (Robinson 1994). In a few cases, sense data have been equated with portions of the surface of a material object (Moore 1918–19: 23–24; Bermúdez 2000).