Language, i. e. spoken language, is one aspect of human activity. A human being communicates with others in daily life, and language is one of the media of their communication. However, it is not a thing outside of him, but a phonomenon found in his activity itself.
It is a social custom learned after his birth, but his mother influences him not only after the birth, but also possibly when he is still in her womb.
A human being can easily become bilingual, trilingual, etc, if he learns the languages probably before his puberty. Adult people, however, find it difficult to learn a foreign language. It is necessary to scientifically confirm when and how his ability of learning his mother tongue solidifies.
There are a few people who can exactly recite extremely long poems or historical legends, but everyone does not have such an ability. However, everyone can freely speak his native language.
The languages in the world have various structures and systems, but certain circumstances necessitate them to have common features.
Utterances can be short, long, or extremely long. One utterance includes one or more sentences, and one sentence includes one or more words. Why has an utterance such a structure?
It is impossible to memorize whole sentences uttered by various people, to say nothing of whole utterances, because kinds of sentences are almost infinite and there is no limit of the length of sentences. However, one language has a finite set of words, and everyone can learn before his puberty the basic vocabulary at least with the grammatical rules which combine words into sentences.
Words are combinations of a meaning (a concept) with a sound-shape. Children automatically acquire the concepts of the things and events in daily life, and they learn to combine a concept with a sound-shape which is approved by the linguistic community.
In order to discriminate several thousand words of one language, the sound-shapes of words necessarily have some definite structure. Therefore, they are combinations of syllables, which consist of one or more consonants plus a vowel or a diphthong (plus one or more consonants).
The set of consonants or vowels (and diphthongs) is not a random one, but a systematic one, so that it is easy to memorize them.
The sets of consonants and vowels can be systematic on account of the distictive features, which are very easy for a human being to memorize, because they are due to the articulations which are innately possible for him.