 According to the indirect realists, this directness is an illusion; we are in fact directly aware of experiential intermediaries, and we perceive the extramental world only indirectly, in virtue of being directly aware of these intermediaries. Most early indirect realists (e.g., Moore 1903, 1939; Russell 1912; Price 1950) thought of these intermediaries as phenomenal or mental particulars, typically called  sense-data.  Consider a hallucination of a red apple. Intuitively, the person having the hallucination seems to see something. This something is not, of course, an apple. But it is an object, according to sense-datum theorists, which is shaped like an apple and is really red. It is a sense-datum, a phenomenal (mental) individual which really has the qualities that it visually appears to have. Sense-data, however, are no ordinary objects: they are private, subjective, self-intimating, and the source of incorrigible knowledge. According to sense-datum theorists, sense-data are internal to one’s consciousness: they are not before one’s sense-organs. These theories claim that there is a hidden act-object structure in the perceptual awareness itself. Every perceptual awareness involves the act of being aware of phenomenal objects and their qualities that phenomenally determine this perceptual awareness, whether or not this awareness is a hallucination or a veridical perception of external objects.