We review concepts such as: Morpheme, morph, allomorph, suffix, prefix, prefix, circumfix, thematic vowels, interphases, infixes ... and explain how to analyze the internal structure one word: segmentation, commutation and recurrences of morphs, problems in segmentation : Amalagama, alomorfia, zero morph, empty morph, homonymy, supplementation, families with wealthy and educated voices, synonymy and polysemy of morphosms ... The system of brackets and tree is proposed to give an account of the internal hierarchical structure of word.