Classifying Words in Japanese.

Japanese word break down into 2 main categories (jiritsugo and fuzokugo) which then both break down into smaller subcategories.

Jiritsugo (自立語) means words (語) that stand (立) by themselves (自); these words carry the meanings in a sentences and in that respect could be compared to the open word class in the English language as at their base forms both contain their language equivalent of nouns, verbs , adjectives, adverbs ect. 

However jiritsugo words are then broken down further into katsuyōgo and mukatsuyōgo. These are respectively, words that can be inflected and words that cannot be inflected. The katsuyōgo category has 3 types of words in it; verbs, '-i' adjectives and '-na' adjectives. 

Verbs in Japanese have a very simple inflectional pattern as they are all either a group 1 '-u' verb, a group 2 '-ru' verb or a group 3 which contains the two irregular verbs 'kuru' and 'suru'. All of these groups then have rules which allow the verb to be changed from the original jisho (dictionary) form into it's other forms, i.e. the -masu form which is the present tense of Japanese verbs. 

 There are also two kinds of adjectives in Japanese. Adjectives ending in '-i' that are known as keiyōshi and adjectives that end in '-na', keiyōdōshi. The keiyōshi are heavily related to verb phrases in English languages, for example the word 'akai' meaning 'red' would then be inflected to akakatta which changes the tense to past and the meaning to 'was red'. Keiyōdōshi are more closely related to adjectival nouns and more comparable to the adjectives of the English language, words like hansamuna (handsome), kireina (pretty or clean). 

Japanese adverbs (fukushi) cannot in inflected and fall under the second category in jiritsugo words, mukatsuyōgo. These adjectives are made by changing the ending of an adjective to create the adverb, in the same manner as adding the morpheme -ly to end of a word creates an adverb. This can be seen in Japanese by adding '-ku' to the end of '-i' adjectives. For example hayai hito means 'fast person' but hayaku kitte means come quickly.

Mukatsuyōgo also contains Japanese nouns (meishi) which means the naming part of speech which is the same as English nouns. As well as setsuzokushi (conjunctions) and rentaishi (prenominals). 

Fuzokugo (付属語) are words with no meaning and only serve to add the the grammatical set up of a sentence. Joshi (particals) are words like wa and ka which serve as subject and topic markers. These aren't really seen in English language and often are very confusing for speakers of English to grasp when learning Japanese.