Middle Irish is a fusional, VSO, nominative-accusative language.
Nouns decline for two genders: masculine, feminine, though traces of neuter declension persist; three numbers: singular, dual, plural; and five cases: nominative, accusative, genitive, prepositional, vocative. Adjectives agree with nouns in gender, number, and case.
Verbs conjugate for three tenses: past, present, future; four moods: indicative, subjunctive, conditional, imperative; independent and dependent forms. Verbs conjugate for three persons and an impersonal, agentless form (agent). There are a number of preverbal particles marking the negative, interrogative, subjunctive, relative clauses, etc.
Prepositions inflect for person and number. Different prepositions govern different cases, depending on intended semantics.