 A. J. Ayer (1940), contra Price and others, argued that the existence of sense data is not a factual question but a matter of linguistic convention. He held that all theorists of perception might agree on the phenomenal facts about seeing pennies but disagree on the implications for the real shapes of pennies. One theorist holds that, as the observer changes position, the penny appears elliptical but stays round; the theorist endorses sense data (by Illusion). Another theorist agrees about the series of elliptical appearances with a moving observer but holds that, when the penny looks elliptical, it has changed shape to become elliptical (Ayer 1940: 17–18). According to Ayer, the competing theories can’t be differentiated empirically (they agree on the elliptical appearances) and so they become recommendations about perceptual language. Ayer (1940: ch. 1) found that the Argument from Illusion supports choosing sense-data language. He developed the language of phenomenalism, in which statements about material objects are understood as statements about actual and possible sense data (1940: ch. 5). In his scheme, even though sense data do not exist unsensed (possible sense data are merely hypothetical), they need not be classed as mental states (1940: 76–78). Ayer (1940: 61–65) departed from the other main theorists in rejecting an act-object analysis of sensations and their objects  (item 8).