The purpose of this paper is to make a sentence systemic within the category of structural grammar for the modality in which a speaker expresses his attitude. It is the priority of a language to communicate meaning. By eliminating the theoretical description of traditional grammar, this paper also aims to illustrate the concepts of nine modal verbs through a systemic network. The concept of modality includes both the epistemic and the deontic characteristics of modality. Epistemic modality is associated with either knowledge or belief on the part of a speaker who gives his own judgments about the state of affairs, events, or actions. However, deontic modality is related to either the possibility or the necessity of acts that a speaker performs to give permission or fulfill an obligation. In conclusion, all the subsystems are described within the framework of the systemic network, with the intention of including all the potential options of the semantic functions available in a situation.