In the first part, this article shows that the notion of transcategoriality, which is present in several types of languages (inflectional, isolating, agglutinative), serves to reconcile two antinomic forces of human linguistic activity: to satisfy cognitive-communicative needs and to limit the effort/to optimise linguistic systems. In the second part, the article examines a triangular dynamic model which comprises three macro-categories, namely lexeme, grammeme, pragmateme, and then, it discusses the differences between these three macro-categories. In the third and last part, it argues for the existence of transcategoriality in Vietnamese, an isolating language without inflectional morphology. It discusses this issue by analyzing some markers such as: thành công, đẹp, mới, thì, and mà.