  The sense-datum theory is usually taken to be a form of phenomenism; it will be treated as such  here.[39]  According to the sense-datum theorist, sense-data that are associated with experiences of seeing the sky, lapis lazuli, cobalt glass, etc., have a distinctive property; the traditional sense-datum theorist took this property to be the color blue (see, e.g., Moore 1953, 30, n.2), but let us speak more neutrally and call it ‘blue\('\)’ (Peacocke 1983, Ch. 1). Then, according to the sense-datum theorist, the phenomenist equation can be spelled out more informatively thus: