  As adults, we recognize physical objects as bounded entities that persist through space and time; they ‘hold together’ as units, and their paths, when they move, are continuous. In addition, objects causally interact upon contact with each other. Do we learn these properties of objects by experience, and if so, by what sort of experience? Empiricist thinkers have argued that these properties are learned, and have proposed several different types of experience as requisite input to such learning. Helmholtz (1867/1962) suggested that moving around objects and manipulating them were necessary for building a concept of an object. Quine (1960) looked to language as the relevant source of information, and Piaget (1954) proposed that sensorimotor coordinations led to construction of the concept of a physical object. Indeed, Piaget famously argued that infants altogether lack object permanence (1977), the understanding that objects persist in time and space, until the latter half of the second year of life.