Abstract: We investigated the proposition understanding of children 8-10 year of age,adolescents and adults.128 participants took part in our test.We used the proposition-figure match task and tested all of the 5 kinds of proposition.Our results support three main conclusions:(A) Young children are capable of propositional reasoning which is contrary to the claims of Piaget.The youngest subjects were able to draw valid conclusions well above chance to one model proposition;(B) Our findings corroborate the model theory of propositional reasoning which suggests that reasoning depends on a mastery of referential language and on the ability to search for counterexamples.Most of the subjects performed better with one-model proposition than with multiple-model proposition.(C) There is a significant development of ability from childhood to adulthood,especially in the multiple-models proposition.And it is possible to identify some of the major components of the improvement.

Key words: Deductive reasoning, proposition understanding, development, mental model theory