At the beginning of the twentieth century, since external phenomena often mask the essence of reality, the French linguist Gustave Guillaume recommended that il would be insufficient to observe external phenomena, linguistic facts. The psychomechanics of language formulated by Gustave Guillaume follows the strategy of observing the essence through external phenomena, recommends studying the mental structures preceding the speech act through speech. Inherited from psychomechanics of language, Samir Bajrić’s linguistic neoteny is largely based on the observation of the speaker’s metal spaces and seeks to reveal the cognitive relationships between the speaker and the language during appropriation of one language or another language. Inspired by biological neoteny, linguistic neoteny is interested in human particularities due to neotenic phenomena; while respecting the rule of functionality, the process of appropriation of the language is accompanied by that of the growth of the speaker. On this context, on the one hand, we are going to elucidate the mutation of cognitive relations between the speaker and the language that he learns successively by a binary approach as well as by a ternary approach; on the other hand, we will reveal the philosophical foundation of linguistic neoteny, namely existential philosophy. Clearly, the initial objective is to elucidate, in a cognitive and philosophical way, the mental spaces of the speaker in the journey towards harmony between man and language.