Multiple developmental studies demonstrate that preverbal infants possess the capacity for complex conceptualization, categorization, and implicit reasoning prior to acquiring language.
The retrieved literature, particularly in developmental psychology regarding preverbal infants (e.g., studies on spatial categories and event sortals), consistently shows that human infants engage in advanced conceptual thinking and mental representation before they develop language. Therefore, the claim that humans are capable of thinking without language is well supported by empirical evidence.