When spoken words are heard, they are decoded in terms of syntax (grammatical construction) and semantics (the meanings of words), generating conceptual thought. When thought (inner speech) is to be communicated through verbalized (outer) speech, meanings are encoded into appropriate vocabulary and syntax. The split between inner and outer speech is the objective manifestation of the split between the decoding and encoding verbal mechanisms. In turn this helps to establish the split between mind and body.
A chimpanzee taught to use sign language can neither arrange symbols syntactically nor can it ask questions. The art of critical argument is intimately bound up with the human ability to think rationally.
Linguistic ability evolves from infancy onwards parallel to the development of mental maturity. The earliest phase is Emotional. The infant is expressing its inner states of emotion or feeling with calls, cries, laughter, etc. and the verbal encoding mechanism plays the dominant role. The second phase is Social: the infant attempts to bring about some reaction in another person through verbal signals, such as through saying 'Mama' to get attention or point something out.
Developing this ability, the infant acquires descriptive vocabulary, and in doing so moves beyond the bounds of animal language to that which is distinctively human. At first this is naively intuitional, but vocabulary is gradually built up representing concrete objects and experiences, and the descriptive function of language comes into full flower. The capacity of the (left hemisphere) decoding mechanism becomes greatly increased. The unique feature of the descriptive function of language is that the statements may be factually true or factually false - the possibility of lying is implicit. And so the discrepancy develops between a specialized verbal left hemisphere, with a tendency to distort and lie, and an emotional, experiential, non-verbal (intuitive) right hemisphere.
Because the reality perceived by the right hemisphere conflicts with alterations (rationalizations, lies and fictions) perpetrated by the left, there is a tendency to negate or suppress the right hemisphere contents, and therefore also intuition, and for the left hemisphere way of seeing the world to become dominant. All of this is clearly demonstrated by the EEG, which differentiates brain arousal of the two hemispheres.
Developing from the specialization of the hemispheres, the third Cognitive phase of linguistic ability is the argumentative function. This includes the ability to ask questions. (Note: a chimpanzee taught to use sign language can neither arrange symbols syntactically nor can it ask questions). The art of critical argument is intimately bound up with the human ability to think rationally.
It is important to recognize that each level of language is permeated by the lower levels. For example, when arguing, there is also expression of feelings, signalling to attempt to obtain the antagonist's attention, and description to underpin the arguments by factual reference. There are also gestural accompaniments to the linguistic expression. A person who is not in touch with his emotions and feelings, however, will be split from such body language, and may be arguing quite to the contrary of what his body is saying. This is the mind-body split.
In the early stages of linguistic development the process of verbal elaboration is very different to the Cognitive phase. In the Emotional phase, language exists to satisfy emotional needs and is largely pre-verbal. Such words as are used are subjective and are associated with emotions and feelings. In the Social phase words are elaborated associatively rather than logically. Associations may be made with the concrete objects represented, both spatially and semantically in terms of differentials such as hot/cold, bright/dark, good/bad, etc. In the first part of childhood this must be so because the child does not possess either sufficient vocabulary or self-awareness to define the words in his mind in terms of other words.
After the age of 8 - 10 years the further development of the internalized language model results from a process of semantic elaboration. In other words, the content of the mind is related to itself by an ever more complex set of connections based on the definitions of words in terms of other words, and through the rules of grammar and logic. The earlier emotional and associative models of language drop from sight; the Semantic model becomes available to introspection and the split between inner and outer speech widens.