Translation guide
In Japanese, nouns do not decline for case, number, or gender. Instead, grammatical relationships are shown by particles. Verbs and adjectives conjugate, but this is usually called 'conjugation', not 'declension'. This guide covers how to express the concept of declension when talking about language, and how to handle what declension does in English (showing case, number, gender) in Japanese.
The learner wants to discuss the grammatical phenomenon of declension, e.g., in Latin, German, or Russian.
The standard linguistic term for 'declension' (of nouns, pronouns, adjectives). Used in academic contexts.
Latin nouns have five declensions.
Literally 'case change'. Often used to refer to case inflection specifically, but can be used more broadly for declension.
Declension is important in German.
A broader term meaning 'inflection' or 'word form change', covering both declension and conjugation. Less precise but understandable.
This language has complex inflection.
The learner wants to know how to mark the role of a noun (subject, object, etc.) in a Japanese sentence, which is what declension does in many languages.
Japanese uses postpositional particles to indicate grammatical case. The most common are が (subject), を (object), に (indirect object/location), の (possessive), etc. These are not part of the noun itself but separate words.
The dog chased the cat.
In casual speech, particles are often dropped if the meaning is clear from context. The basic word order SOV helps identify roles.
The dog chased the cat. (casual)
The learner wants to indicate whether a noun is singular or plural, a common function of declension in many languages.
Japanese nouns generally do not change form for number. 本 can mean 'book' or 'books'. Number is inferred from context or specified with quantifiers.
I read a book / books.
To explicitly state quantity, use a number with a counter and の. This is not declension but a separate construction.
three books
The suffix たち can pluralize nouns referring to people or sometimes animals, but it's not a regular plural marker and often implies a group.
The learner wants to know how to indicate grammatical gender, as in languages with masculine/feminine/neuter nouns.
Nouns do not have gender. There are no articles or adjective agreements based on gender. Natural gender is expressed lexically (e.g., 男の子 'boy', 女の子 'girl').
That person is a teacher. (gender neutral)
In Japanese linguistics, 曲用 (declension) is for nouns, while 活用 (conjugation) is for verbs and adjectives. English speakers often use 'declension' loosely, but in Japanese, these are distinct terms.
verb conjugation
If you need to say 'declension' in everyday Japanese, 曲用 is understood by educated speakers, but you can also paraphrase: 「名詞の形が変わること」(the way nouns change form).