According to Lev Vygotsky :

The correct answer is Language development facilitates cognitive development.

Lev Vygotsky, a prominent Soviet psychologist, proposed the Sociocultural Theory of Cognitive Development. According to Vygotsky, learning and cognitive development are inherently social processes deeply rooted in cultural context and language interactions.

Key principles of Vygotsky's theory regarding language and cognitive development include:

1. Language as a Tool for Thought: Vygotsky argued that language is the primary tool through which children acquire knowledge and organize their thinking. Initial speech functions socially, but gradually becomes internalized into private speech (self-talk) and inner speech, which directly guides cognitive processes, problem-solving, and self-regulation.

2. Language Facilitates Cognitive Development: Unlike Jean Piaget, who believed that cognitive development must precede language development, Vygotsky emphasized that language plays a profound role in shaping and accelerating cognitive development. Acquiring language provides children with concepts, categories, and logical structures necessary for higher-order cognitive functions.

3. Social Interaction: Social interaction and cultural tools, particularly language, act as mediators in a child's Zone of Proximal Development (ZPD), helping them transition from simple mental functions to complex cognitive abilities.

Therefore, according to Lev Vygotsky, language development actively facilitates cognitive development.