What phenomenon illustrates 'linguistic creativity' in children according to the discussion of behaviorism?

The phenomenon of using incorrect past tense forms, such as saying "runned" instead of "ran," effectively illustrates linguistic creativity in children. This creative usage reflects a child's understanding of language rules and their playful application of these rules to generate new forms.

Children learn language through exposure and mimicry; however, when they apply grammatical rules, they often do so in novel ways. For instance, children learn that many verbs take an '-ed' form to indicate the past tense, and they apply this pattern even when it leads to an incorrect form. This tendency showcases their ability to creatively use the rules of language they have acquired, rather than merely rote repeating what they hear from adults.

In contrast, the other options presented do not illustrate the same level of creativity. Using correct past tense forms indicates compliance with grammatical rules rather than creativity. Creating new words does demonstrate creativity but may not directly relate to the behavioral aspect of language acquisition emphasized in behaviorism. Lastly, forming sentences only heard from adults reflects imitation rather than the inventive process of language creation demonstrated by using incorrect verb forms.