Psychologists know that reasoning human beings do not spontaneously follow the rules of formal logic when using implication. Addressing this phenomenon, Piaget employed the concept of "significant implication," which exists when the meaning of a subsequent proposition is "included" in the meaning of an earlier one, and is not merely correlated. Appearing early in the development of the child, significant implication was thought to be the precursor to children's comprehension of necessity. Piaget also differentiated between proactive implications, which are reasons for preceding implications, and retroactive implications, which depend on the questions subjects are capable of asking as they work on understanding. Two studies were conducted to investigate whether individuals' capacity to correctly use implication is linked to possession, in a given situation, of a model organizing meanings in terms of reason. Results of a developmental study of children between 5 and 13 years of age indicated that their ability to manipulate implication depended on the richness of a model each subject had established or that he or she was capable of establishing. Adult subjects correctly manipulated implications when in a situation within which they could reorganize and/or transform meanings, as they searched for the reasons permitting them to do so. Implications of the findings for researchers are briefly discussed. (RH)