Different Origins of Language and Thought

The Russian psychologist Lev Vygotsky argued that thought and language develop separately in a child until about two years of age, when they merge. Before two years, thought is preverbal and experienced more in action (Piaget's sensorimotor stage); a child's earliest utterances, such as crying when uncomfortable, are more automatic reflexes than thought-based. Around two years of age, a child expresses thought verbally, and speech begins to reflect rationality; children then become able to manipulate thoughts using soundless speech. Vygotsky believed that during this period, the development of language and thinking become interdependent — conceptual thinking depends on the quality of inner speech and vice versa.

Thought is used without language when the vehicle of thinking is non-verbal, such as visual or movement-related. Language is used without thought when expressing feelings or exchanging pleasantries, for example, 'Good morning! How are you?' 'Very well, I am fine.' When the two functions overlap, they can be used together to produce verbal thought and rational speech. …