Functional grammar analyzes language based on choices and how grammar constructs meaning in context. It looks at analyzing experience, interaction, and message construction. Functional grammar in ESP deals with analyzing processes, participants, circumstances, mood, modality, and clause combining. Notional grammar expresses ideas and social behaviors that do not vary across languages. Functional grammar is useful for ESP as it focuses on actual language use and human thinking. Some advantages are that it provides an inventory of language elements and is based on factual study of language use.