The lectures held at the Sorbonne in 1942 provide a clear summary of Jean Piaget's developmental psychological research up to that point. In particular, his detailed engagement with Gestalt theory offers insight into his theory development and patterns of argumentation. Through his analysis and critique of Gestalt theory, he concludes that perception cannot be the fundamental mechanism of intelligence development, but rather that it is based on actions. Since these actions take place in a space, the operations—internalized actions—have a mathematical structure. Piaget traces their development across central dimensions and stages, taking into account both social and biological-psychological factors.