Japanese nouns have no grammatical number, gender or article aspect. The noun hon (本) may refer to a single book or several books; hito (人) can mean "person" or "people"; and ki (木) can be "tree" or "trees". Where number is important, it can be indicated by providing a quantity (often with a counter word) or (rarely) by adding a suffix. Words for people are usually understood as singular. Thus Tanaka-san usually means Mr./Ms. Tanaka. Words that refer to people and animals can be made to indicate a group of individuals through the addition of a collective suffix (a noun suffix that indicates a group), such as -tachi, but this is not a true plural: the meaning is closer to the English phrase "and company". A group described as Tanaka-san-tachi may include people not named Tanaka. Some Japanese nouns are effectively plural, such as hitobito "people" and wareware "we/us", while the word tomodachi "friend" is considered singular, although plural in form.
Verbs are conjugated to show tenses, of which there are two: past and present, or non-past, which is used for the present and the future. For verbs that represent an ongoing process, the -te iru form indicates a continuous (or progressive) tense. For others that represent a change of state, the -te iru form indicates a perfect tense. For example, kite iru means "He has come (and is still here)", but tabete iru means "He is eating".
Questions (both with an interrogative pronoun and yes/no questions) have the same structure as affirmative sentences, but with intonation rising at the end. In the formal register, the question particle -ka is added. For example, Ii desu (いいです。) "It is OK" becomes Ii desu-ka (いいですか？) "Is it OK?". In a more informal tone sometimes the particle -no (の) is added instead to show a personal interest of the speaker: Dōshite konai-no? "Why aren't (you) coming?". Some simple queries are formed simply by mentioning the topic with an interrogative intonation to call for the hearer's attention: Kore-wa? "(What about) this?"; Namae-wa? (名前は？) "(What's your) name?".
Negatives are formed by inflecting the verb. For example, Pan-o taberu (パンを食べる。) "I will eat bread" or "I eat bread" becomes Pan-o tabenai (パンを食べない。) "I will not eat bread" or "I do not eat bread".
The so-called -te verb form is used for a variety of purposes: either progressive or perfect aspect (see above); combining verbs in a temporal sequence (Asagohan-o tabete sugu dekakeru "I'll eat breakfast and leave at once"), simple commands, conditional statements and permissions (Dekakete-mo ii? "May I go out?"), etc.
The word da (plain), desu (polite) is the copula verb. It corresponds approximately to the English be, but often takes on other roles, including a marker for tense, when the verb is conjugated into its past form datta (plain), deshita (polite). This comes into use because only keiyōshi adjectives and verbs can carry tense in Japanese. Two additional common verbs are used to indicate existence ("there is") or, in some contexts, property: aru (negative nai) and iru (negative inai), for inanimate and animate things, respectively. For example, Neko ga iru "There's a cat", Ii kangae-ga nai "[I] haven't got a good idea". Note that the negative forms of the verbs iru and aru are actually i-adjectives and inflect as such, e.g. Neko ga inakatta "There was no cat".
The verb "to do" (suru, polite form shimasu) is often used to make verbs from nouns (ryōri suru "to cook", benkyō suru "to study", etc.) and has been productive in creating modern slang words. Japanese also has a huge number of compound verbs to express concepts that are described in English using a verb and a preposition (e.g. tobidasu "to fly out, to flee," from tobu "to fly, to jump" + dasu "to put out, to emit").
There are three types of adjective (see also Japanese adjectives):
形容詞 keiyōshi, or i adjectives, which have a conjugating ending i (い) (such as あつい atsui "to be hot") which can become past (あつかった atsukatta "it was hot"), or negative (あつくない atsuku nai "it is not hot"). Note that nai is also an i adjective, which can become past (あつくなかった atsuku nakatta "it was not hot").
暑い日 atsui hi "a hot day".
形容動詞 keiyōdōshi, or na adjectives, which are followed by a form of the copula, usually na. For example hen (strange)
変なひと hen na hito "a strange person".
連体詞 rentaishi, also called true adjectives, such as ano "that"
あの山 ano yama "that mountain".
Both keiyōshi and keiyōdōshi may predicate sentences. For example,
ご飯が熱い。 Gohan-ga atsui. "The rice is hot."
彼は変だ。 Kare-wa hen da. "He's strange."
Both inflect, though they do not show the full range of conjugation found in true verbs. The rentaishi in Modern Japanese are few in number, and unlike the other words, are limited to directly modifying nouns. They never predicate sentences. Examples include ookina "big", kono "this", iwayuru "so-called" and taishita "amazing".
Both keiyōdōshi and keiyōshi form adverbs, by following with ni in the case of keiyōdōshi:
変になる hen ni naru "become strange",
and by changing i to ku in the case of keiyōshi:
熱くなる atsuku naru "become hot".
The grammatical function of nouns is indicated by postpositions, also called particles. These include for example:
が ga for the nominative case. Not necessarily a subject.
彼がやった。Kare ga yatta. "He did it."
に ni for the dative case.
田中さんにあげて下さい。 Tanaka-san ni agete kudasai "Please give it to Mr. Tanaka."
It is also used for the lative case, indicating a motion to a location.
日本 に行きたい。 Nihon ni ikitai "I want to go to Japan."
の no for the genitive case, or nominalizing phrases.
私のカメラ。 watashi no kamera "my camera"
スキーに行くのが好きです。 Sukī-ni iku no ga suki desu "(I) like going skiing."
を o for the accusative case. Not necessarily an object.
何を食べますか。 Nani o tabemasu ka? "What will (you) eat?"
は wa for the topic. It can co-exist with case markers above except no, and it overrides ga and o.
私はタイ料理がいいです。 Watashi wa tai-ryōri ga ii desu. "As for me, Thai food is good." The nominative marker ga after watashi is hidden under wa. (Note that English generally makes no distinction between sentence topic and subject.)
Note: The difference between wa and ga goes beyond the English distinction between sentence topic and subject. While wa indicates the topic, which the rest of the sentence describes or acts upon, it carries the implication that the subject indicated by wa is not unique, or may be part of a larger group.
Ikeda-san wa yonjū-ni sai da. "As for Mr. Ikeda, he is forty-two years old." Others in the group may also be of that age.
Absence of wa often means the subject is the focus of the sentence.
Ikeda-san ga yonjū-ni sai da. "It is Mr. Ikeda who is forty-two years old." This is a reply to an implicit or explicit question who in this group is forty-two years old.
source : wikipedia