Based on a series of 12 experiments with deaf persons, this study shows that oral language is not the necessary condition for conceptualization. It reaches the conclusion that “logical, intelligent thinking does not need the support of a symbolic system, as it exists in the living language of society.” The study demonstrates that the thinking processes of the deaf can be explained without recourse to language. The author suggests that “a non-verbal approach to thinking may be a fruitful one for studying thinking in general.”