Abstract Sortal concepts provide children with criteria for the categorical differentiation of count nouns and mass nouns in languages with a count/mass distinction. This article discusses the paradox encountered by Carey in her empirical studies of the continuity hypothesis , the view that innate infant perception of qualities and objects is identical to adult categorization in general (e.g. Pinker, 1984; McNamara, 1982). This view contrasts with the discontinuity hypothesis , the view that infant perception of qualities and objects is of an entirely different order from adult conceptualization of categorization and sortal plurality (e.g. Quine, 1960, 1969, 1973). Unfortunately, Carey's interpretation of her empirical studies leads to a paradox: she finds evidence for both continuity and discontinuity. Contrary to Quine's predictions, she finds evidence for adult-like infant perception of persistent physical objects by 4 months of age, but finds that children do not perceive ‘other kinds’ of sortal classification in an adult-like way until at least, 11 months of age, a surprising discontinuity. We argue that Quine and Carey both erroneously construe the perception of persistent physical objects as a sortal concept. We deploy the semiotic theory of C.S. Peirce (1839–1914) to analyze the studies presented by Carey and thereby reconcile the paradoxical interpretations of her empirical evidence. Contrary to Quine and Carey's common assumption, we claim that children's perception of physical objects (part of Peirce's proposed second category of innate conceptualization) is independent from the later development of true sortal categorization (a derived complication of Peirce's third innate category). In the Peircean analysis there is a fundamental continuity in the overall process of conceptual and linguistic acquisition from birth to adulthood, but at the same time, the Peircean model accounts for differences in cognitive and linguistic abilities empirically demonstrated to exist, between infants, young children, and adults.