Although Piaget’s fame belongs to experimental psychology and to the science of cognitive development, he himself conceived his work as providing a synthesis of biology, epistemology, and logic. He worked in terms of a dynamic model of learning, or dialectical progression (see Hegel) in which perceptual inputs are modified by existing structures of knowledge (‘assimilation’) and these in turn are modified to ‘accommodate’ the inputs (see also reflective equilibrium). His empirical methods with young children have proved controversial, the question being whether what he regarded as levels of development were more the artefact of children not properly understanding questions they were being set. However, his status as a pioneer of naturalized epistemology is assured. Influential books included The Language and Thought of the Child (1923, trs. 1926) The Child’s Conception of the World (1926, trs. 1929) and The Child’s Conception of Physical Reality (1926, trs. 1960).