What is mastered in Brown's third stage of language development?

In Brown's third stage of language development, children typically master the use of possessive -s. This stage, often observed in children aged 2.5 to 3 years, marks a significant advancement in their language skills, particularly in expressing ownership and relationships. The possessive form allows children to construct more complex sentences and communicate their thoughts more effectively, indicating their understanding of noun relationships.

Mastery of possessive -s is crucial because it reflects not only grammatical understanding but also cognitive development around personal identity and the concept of ownership. Children begin to form possessive phrases like "Mommy's hat" or "Johnny's toy," which shows their ability to use language as a tool for social interaction and expression of their environment.

The other options relate to different aspects of language development occurring in earlier or later stages. For instance, plural -s generally appears earlier in development, while past tense -ed and present progressive -ing typically occur after the mastery of possessive forms. Each of these morphemes represents important milestones in a child's linguistic growth, but in the context of the third stage, possessive -s is the key focus.