维果茨基还强调了语言的出现在区分人类和其他动物方面的重要性。在维果茨基看来，语言是影响儿童认知发展的最重要的心理工具。通过获得知识，儿童获得了以新的方式思考的手段，并获得了理解世界的新的认知工具。对维果斯基来说，思维和言语的分析是心理学的一项主要任务，而核心问题是“思维与言语的关系”(Gredler, 2005)。他确定了儿童使用语言的三个不同阶段。首先，语言主要用于交流。它指的是社交用语。对维果斯基来说，语言开始独立于思想而发展。然后，思考变成了语言，孩子们开始使用以自我为中心的或私人的语言来引导他们自己的思考。皮亚杰和维果茨基都注意到，在解决问题时，学龄前儿童会自言自语。皮亚杰把这种自我导向的行为称为以自我为中心的言语，维果茨基把它称为一种私人言语。他认为，私人谈话起源于儿童与其他人的互动以及这些互动;他们开始使用父母的指导意见来规范自己的行为。自言自语，如在执行任务时大声说话或低语，是指自言自语。研究表明，儿童在面对更具挑战性的任务时，往往会增加自言自语的次数(Gredler, 2005)。孩子们开始使用私人语言来组织(计划、指导或评估)他们的行为。私人语言的使用在学龄前达到高峰，然后下降。对维果斯基来说，这种私人话语的减少首先会转化为内在话语，然后转化为言语思维。在语言发展的最后阶段，以自我为中心的话语变成了内在的话语，儿童开始用内在的话语来引导他们的思维和行为。内心的话语是为自己说话，而不是没有言语的交流.
Vygotsky also gave importance the emergence of speech in terms of distinguishing humans from other animals. In Vygotksy’s view, language was the most important psychological tool that influences children’s cognitive development. By acquiring knowledge a child is supported the means to think in new ways and obtains a new cognitive tool for making sense of the world. For Vygotsky, the analysis of thinking and speech was a major task for psychology, and the central problem was “the relationship of thought to word” (Gredler, 2005). He identified three different stages in children’s use of language. At first, language is primarily used for communication. It refers social speech. For Vygotsky, speech begins to develop independent of thought. And then, thinking becomes verbal and children begin to use egocentric or private speech to guide their own thinking. Both Piaget and Vygotsky observed that as in problem solving situations pre-school children talking to themselves. While Piaget referred the self directed behavior as egocentric speech, Vygotsky labeled to it as a private speech. He claimed that private speech originated in the children’s interaction with other people and with these interactions; they start to use their parent’s instructional comments to regulate their own behavior. Private speech such as talking aloud or whispering while performing a task refers speech for oneself. Researches indicated that children tend to increase the amount of self-talk when facing more challenging tasks (Gredler, 2005). Children start using private speech to organize (plan, direct, or evaluate) their behaviors. The use of private speech peaks during preschool years and then decreases. For Vygotsky, this decrease with private speech turns first into inner speech and then into verbal thinking. At last stage of language development, egocentric speech becomes inner speech and children start to use inner speech to guide their thinking and actions. The inner speech is speech for oneself, not for communication without words