The particle は is what's called a kakari-joshi 係助詞. This class of particles are special in that they require the predicate to be in a particular form. In the case of the particle は, the sentence must be in the predicative form (shūshikei 終止形).
What is a "Topic"?
i. To understand は, we need to know what is meant by “topic.” The topic (shudai 主題) of a sentence can be an animate or inanimate entity (of one or more components), and that entity is what provides a starting point for conversation. A topic must also be something based on previously established information, whether it be from the ongoing conversation, one not too far back in the past, or from common sense.
The topic is considered to be “old information.” In order for something to be registered information, though, you may need to use ga が first to establish it. Essentially, information needs to be new before it can be grammatically treated as old information. This distinction between new information and known information is exemplified in Ex. 1.
1. 昔々、あるところに、おじいさんとおばあさんが住んでいました。おじいさんは山へ柴刈りに、おばあさんは川へ洗濯に行きました。
Mukashi mukashi, aru tokoro ni, ojiisan to obāsan ga sunde imashita. Ojiisan wa yama e shibakari ni, obāsan wa kawa e sentaku ni ikimashita.
Long, long ago, there lived an old man and woman. One day, the old man went to the mountains to gather firewood, and the old woman went to the river to wash clothes.
This sentence is the opening to one of the most important fairy-tales of Japan, Momotarō 桃太郎. At the beginning, the reader doesn't know anything about the story. This is why the particle が is used to mark the subject. Once the characters are established, they are then treated as the topic in the following sentence, thus marked by は. Note that although the comment that follows may still be new information, the topic itself is no longer new.
2. あれは私の帽子です。
Are wa watashi no bōshi desu.
That's my hat.
Although the comment, the hat being the speaker's, is "new information," the recognition of the hat is not.
In Japanese, phrases may be topicalized and put at or near the front of the sentence, after which point a comment is made about said topic. The comment could be already known or new information, but the topic is something implied to be known to both speaker and listener(s). The topic, as mentioned above, is deemed to be an entity known to others and oneself. Often times, this is based on a common sense assessment of reality.
3. お名前は何ですか。
O-namae wa nan desu ka?
What's your name?
Sentence Note: Everyone has a name. Even if this statement weren't completely true, it's practically true. This is all the information one needs to know about the human world to understand how "your name" can be grammatically treated as "old/registered" knowledge. You know the person you're talking to has a name; you just don't know what that person's name is, which is why the question forms the comment about the topic.
4. トイレはどこですか。
Toire wa doko desu ka?
Where is the toilet?
Sentence Note: When you ask this to someone, you're assuming that there is a toilet nearby. The existence of toilets can be rather easily ascertained based on one's surroundings. The fact that you're asking this means you've already determined that there is one, and you're also implying that the existence and knowledge of its location is something that others might help you find out.
5. 火星は赤いです。
Kasei wa akai desu.
Mars is red.
Sentence Note: Most people know about Mars. It has been a part of human fascination for a long time, and so the acknowledgment of its existence is well established. It being red is also something that is so well known that it can be viewed as a generic statement.
6. 日本は島の国です。
Nihon wa shima no kuni desu.
Japan is an island nation.
Sentence Note: Japan is known by most people as an island nation.
7. ウサギはかわいいですね。
Usagi wa kawaii desu ne.
Rabbits are cute, aren't they?
Sentence Note: Wherever rabbits exist, there are humans that know about them.
The Zero-Pronoun
ii. Whenever the topic is semantically the same as the subject or even the object of a sentence, the particle は does not mark both. It only functions as the topic marker. All sorts of things can be topicalized, which makes it seem like は has far more functions than it actually does. Semantically, it is very similar to the English expression “as for X.” It's the "X" in this expression that は stands for, and nothing more. However, using “as for” heavily in translation will result in unnatural English. Using one’s own intuition on what is proper English will come to play here. Nonetheless, it's a perfect stepping stone for understanding how this particle functions grammatically.
8a. 私は毎日ジムに行きます。
Watashi wa mainichi jimu ni ikimasu.
I go to the gym every day.
Ex. 8a can alternatively be translated as, “As for me, I go to the gym every day.” The purpose of は is two-fold. It establishes that “I” is the topic, but it also differentiates it from other possible topics like “he” or “she.” As such, the reason why watashi 私 would even be used instead of just being dropped—which is usually the case—is because the speaker has become the center of conversation. Although the subject of this sentence is “I,” the 私 of this sentence corresponds to the "me" in “as for me.” The “I” that corresponds to the subject is not spoken because it would be semantically redundant. In fact, watashi wa watashi ga 私は私が is ungrammatical.
This is where the concept of a zero-pronoun comes into play. A zero-pronoun is a pronoun used to refer to the subject of a Japanese sentence when it is omitted because it is juxtaposed with a topic that happens to be the same thing. It is the grammatical fix to the grammaticalized rule of omitting semantically redundant elements. More broadly, a zero-pronoun is used in place of an entity that is semantically the same as the topic. Thus, this can be applied to other situations as we will see as well. With a zero-pronoun in mind, we can view 8a as follows:
8b. 私は毎日ジムに行きます。
Watashi-wa (ø-ga) jimu-ni ikimasu.
As for me, (I) go to the gym every day.
ø = Watashi 私
9a. ケーキはもう食べました。
Kēki wa mō tabemashita.
The cake, I already ate it.
Grammar Note: The particle は appears to mark the direct object, but in reality, it simply marks the topic which also happens to be the object, but the object is expressed with an unexpressed zero-pronoun. Thus, Ex. 9a can be viewed alternatively as follows:
9b. ケーキはもう食べました。
Kēki-wa mō (ø-wo) tabemashita.
The cake, I already ate it.
ø = Kēki ケーキ
The Variety of Topicalized Phrases
iii. The particle は has few restrictions on what it can topicalize. It may topicalize time phrases, location phrases, etc. This is exemplified in the following examples.
10. 日本では地震がよく起きます。
Nihon de wa jishin ga yoku okimasu.
In Japan, earthquakes often happen.
11. 今日は韓国語を勉強します。
Kyō wa kankokugo wo benkyō shimasu.
Today, I will study Korean.
12. 私はお茶です。
Watashi wa ocha desu.
I’ll have tea.
Grammar Note: Whenever learners don’t fully understand the concept of topicalization, they fail to understand that topic ≠ subject. Sentences like Ex. 12 are great examples of this. The underlying subject would be what the speaker wants to drink. This sentence pattern is so famous that it actually goes by the name unagi-bun ウナギ文, with the sentence 私はウナギです (I'll have eel ≠ I'm not eel) being the source of inspiration.
13. こんにゃくは太りません。
Kon'nyaku wa futorimasen.
You won't put on weight from konjac. (≠ Konjac won't put on weight).
Grammar Note: Ex. 13 is another famous example of how different は is from a subject marker. This sentence is referred to by the name kon'nyaku-bun こんにゃく文. These sentences are always explanatory in nature, and what is dropped from the sentence is the 'head' of the attribute phrase. In this case, it's the verb futoru 太る (to put on weight). What is dropped is "food." So, you could rephrase the translation as "Konjac (is a food that) you won't gain weight (from)."
14. 趣味はバスケが兄で、ピアノが姉です。
Shumi wa basuke ga ani de, piano ga ane desu.
As for hobbies, my older brother does basketball and my older sister does piano.
Grammar Note: This is another example of こんにゃく文 where the speaker has chosen not to actual use the word for "to do," and is instead attributing his/her siblings to those activities.
15. こちらは（私の）弟です。
Kochira wa (watashi no) otōto desu.
This is my little brother.
16. 彼女は｛中国人・日本人・アメリカ人・イギリス人｝です。
Kanojo wa [chūgokujin/nihonjin/amerikajin/igirisujin] desu.
She is [Chinese/Japanese/American/British].
17. 中国経済には問題がある。
Chūgoku keizai ni wa mondai ga aru.
There is/are problem(s) in the Chinese economy.
Grammar Note: Due to English phrasing constraints, it may not always be possible to place the topicalized phrase of a Japanese sentence at the front of the English translation. However, the fact that the は phrase in question is being topicalized and the fact that said は phrase forms the basis for the upcoming conversation do not change.
18. 私は行きません。
Watashi wa ikimasen.
I won’t go.
19. 彼は先生ではありません。
Kare wa sensei de wa arimasen.
He is not a teacher.
Grammar Notes:
1. Ex. 18 and Ex. 19 are examples of the particle は bringing out the meaning of “X isn’t but something/someone else might be/do Z.” This implicit contrast is something that, depending on the context, may become even more profound (See Usage 2). As for Ex. 19, it could be that another person is a teacher, or "he" could be something other than a teacher. If the particle が were used, the sentences would become examples of exhaustive-listing. Remember, exhaustive-listing is still exhaustive if X simply refers to one entity and one entity only.
2. The は in ではありません is not the topic は. Rather, it is one usage of the contrast marker は (Usage 2).
Generic Statements
iv. Many conversations are started off by mentioning something everyone already knows. However, implying that the listener(s) knows is subjective in nature. This is because one can never definitively know what someone else does or doesn’t know. This usage of は is very different from the exhaustive-listing statements that が can make. Whereas an exhaustive-listing sentence is limited semantically solely to what’s explicitly stated, は is far more open-ended due to its generic nature. There is always a chance for the speaker to imply “I know that X is Z, but I don’t know about Y.”
20. リンゴは果物です。
Ringo wa kudamono desu.
Apples are fruits/Apple is a fruit.
21. 空は青い。
Sora wa aoi.
The sky is blue.
22. 宇宙は広い。
Uchū wa hiroi.
The universe is wide.
23. 太陽は明るい。
Taiyō wa akarui.
The sun is bright.
24. 月は地球の衛星です。
Tsuki wa chikyū no eisei desu.
The Moon is Earth's satellite.
25. 夜は暗い。
Yoru wa kurai.
Night is dark.
26. 花は美しい。
Hana wa utsukushii.
Flowers are beautiful.
27. 春は素晴らしいですね。
Haru wa subarashii desu ne.
Spring is wonderful, isn't it?
28. 世界は小さい。
Sekai wa chiisai desu ne.
The world is small.
Sentence Note: Ex. 28 is actually the translation of the famous tune "It's a small world after all.”
29. 数学は難しいですね。
Sūgaku wa muzukashii desu ne.
Math is difficult, isn’t it?
Sentence Note: As a demonstration of the last point from above, this statement should be interpreted as meaning “I’m not sure about other subjects being hard, but math is, isn’t it?”
Attribute Phrases: X wa は Y ga が
v. As we have actually already seen in our introduction to Japanese grammar, one of the most common ways to describe something is by following a topicalized phrase (X) with は with a neutral statement (Y) followed by が. In the examples below, there are generally two kinds of translations. The first reflects the nature of the Japanese grammar whereas the second rephrases it into more natural English. As you will see, the resulting translation indicates how this grammar is essentially identical to making generic statements.
30. 象は鼻が長い。
Zō wa hana ga nagai.
As for (a/the) elephant(s), their nose(s) are long.
Elephants have long noses.
Grammar Note: It's important to understanding that the topic is elephants, not their noses. The particle が does mark the nose's length as the (new) information of the sentence, but imagine this sentence being the start or part of a longer discussion about elephants. We've actually already learned how the particle no marks attributes. So, you may wonder if the following sentence is correct:
31. 象の鼻が長い。
Zō no hana ga nagai.
Elephant noses are long.
This sentence is, in fact, grammatical, but its nuance is not the same. Focus is placed solely on elephant noses, and the speaker is purposely pointing out their length to the listener.
32. 象の鼻は長い。
Zō no hana wa nagai.
Elephant noses are long.
This sentence is also possible, but now the speaker is just talking about elephant noses with no particular emphasis on the comment.
33. 日本は神社が多い。
Nihon wa jinja ga ōi.
As for Japan, there are many Shinto shrines.
Japan has many Shinto shrines.
34. 秋はサンマが最高だ。
Aki wa samma ga saikō da.
As for autumn, Pacific saury is the best.
In autumn, Pacific saury is the best.
35. 冬には気温が下がります。
Fuyu ni wa kion ga sagarimasu.
In winter, the temperature goes down.
36. その仕事は、私がします。
Sono shigoto wa, watashi ga shimasu.
As for that job, I’ll do it.
37. キリンは首が長い。
Kirin wa kubi ga nagai.
As for giraffes, their necks are long.
Giraffes have long necks.
38. （私は）頭が痛いです。
(Watashi wa) atama ga itai desu.
(As for me), my head hurts.
I have a headache.
39. （私は）お腹が空きました。
(Watashi wa) onaka ga sukimashita.
I’m hungry.
Literally: (As for me), my stomach is empty.
40. （私は）喉が渇きました。
(Watashi wa) nodo ga kawakimashita.
I’m thirsty.
Literally: (As for me), my throat is parched.
Grammar Note: In both Ex. 39 and Ex. 40, it is more natural to drop the pronoun. Although we haven't studied verbal conjugations, it must be noted that the -TA marker at the end of these expressions SHOULD NOT be interpreted as past tense. Instead, it should be viewed as a present perfect tense with a heavy emphasis on the state having reached its state 'now.' When someone says either of these phrases, they're not saying that their "stomach WAS" empty or that their "throat WAS parched." They are experiencing hunger/thirst, so be the better Japanese learner and get them something rather than assume they've already had something.
Questions
vi. As opposed to the questions made with が, those made with は have the interrogative (question) phrase as the predicate. This is because the questions formed with は imply that the question (topic) at hand should be evident/relevant to the listener(s) as well. This pattern will be how most of the questions you ask are formed, and they tend to have a softer tone than does created with が (See Lesson 11).
Word Note: As seen in Ex. 3, when nani 何 (what) is used as the predicate and followed by the copula, it undergoes a sound change and becomes nan なん.
41. サム君はいつ来る？
Samu-kun wa itsu kuru?
When is Sam coming?
42. 今日は何曜日ですか。
Kyō wa nan’yōbi desu ka?
What day is it today?
43.（あなたは）誰ですか。
(Anata wa) dare desu ka?
Who are you?
44. 病院はどこですか。
Byōin wa doko desu ka?
Where is the hospital?
45. 趣味は何ですか。
Shumi wa nan desu ka?
What are your hobbies?
On top of being a topic marker, は is also the particle of contrast (taihi 対比), which can be seen in its usage of marking the topic. There is a line of thought that the contrast meaning of は is actually the primary meaning of は. Within a given sentence, several は may appear. Each one will have a different level of contrast implied. When は doesn't appear to be contrasting anything, it may very well just be used as a topic marker.
46. 私は昨日は昼食は取らなかったんです。
Watashi wa kinō wa chūshoku wa toranakatta n desu.
Yesterday, I didn't have lunch.
Although the presence of 私は could imply a contrast with other people, the sentence is bringing oneself to the forefront of conversation, which would likely be on purpose in this scenario. With this being this case, it is viewed as the topic. Both the words for "yesterday" and "lunch" are marked with は because they contrast with other scenarios. For instance, the speaker may have eaten lunch today, and he may have eaten breakfast and/or dinner that day.
47. 今日は行きます。（→ 明日は行きません）
Kyō wa ikimasu. (→ Asu wa ikimasen)
I'm going today. (→ I'm not going tomorrow)
48. 旦那さんは上海へ行きます。（→ 奥さんは北京へ行きます）
Dan'na-san wa Shanhai e ikimasu. (→ Oku-san wa Pekin e ikimasu)
His/her husband is going to Shanghai. (→ His/her wife is going to Beijing)
49. 大阪へは行きます。（→ 京都へは行きません）
Ōsaka e wa ikimasu (→ Kyōto e wa ikimasen)
I'm going to Osaka. (→ I'm not going to Kyoto)
50. ルールにない事は、私は何も言いません。
Rūru ni nai koto wa, watashi wa nani mo iimasen.
I will say nothing about anything not in the rules.
Grammar Note: The use of 私は adds greater emphasis to the sentence. The speaker is drawing contrast with their stance as opposed to others. The は after koto 事 can also be viewed as both being the topic and a point of contrast. Meaning, the speaker may talk about things in the rules, and the topic is still very much about what is not in the rules.
51. 本当は嬉しいです。
Hontō wa ureshii desu.
I'm actually happy.
Grammar Note: Hontō 本当 is an adverbial noun, and in this sentence, it is being used in the sense of "in actuality." The implication is that although the speaker may not appear happy, they are, in fact, happy.
52. 「日本料理は好きですか」「タイ料理は好きです」
"Nihon ryōri wa o-suki desu ka?" "Tai ryōri wa suki desu."
"Do you like Japanese cuisine?" I like Thai food(, but not Japanese cuisine.)
Grammar Note: The reply provides an indirect means of saying that one doesn't like Japanese cuisine. Although this is inferred by the reply, such responses are deemed politer than just saying no.
53. 犬は好きですが、猫はどうも･･･
Inu wa suki desu ga, neko wa dōmo...
I like dogs, but cats...
Grammar Note: The が seen after です is the conjunctive particle が, which is separate from its use as a subject marker. For now, simply know that it is the "but" in this example and the ones that follow.
54. コーヒーは飲まないが、ビールは飲むよ。
Kōhii wa nomanai ga, biiru wa nomu yo.
I don't drink coffee, but I drink beer.
55. 鉛筆はありませんが、ペンはありますよ。
Empitsu wa arimasen ga, pen wa arimasu yo.
There aren't pencils, but there are pens.
I don't have pencils, but I have pens.
Grammar Note: The verb aru ある may also mean "to have (an inanimate object)."
56. 象の鼻は長いが、象以外の鼻も長い。
Zō no hana wa nagai ga, zō-igai no hana mo nagai.
Elephant noses are long, but there are other noses that are long other than elephants'.
57. 象は鼻が長くて、尻尾が短いです。
Zō wa hana ga nagakute, shippo ga mijikai desu.
As for elephants, their noses are long and their tails are short.
58. 象は確かに鼻は長いが、尻尾はかなり短いです。
Zō wa tashika ni hana wa nagai ga, shippo wa kanari mijikai desu.
As for elephants, their noses are certainly long, but their tails are pretty short.
59. 象（だけ）が鼻が長い。
Zō (dake) ga hana ga nagai.
Elephants (are the (only one's) that have) long noses.
Grammar Note: Although Exs. 56-59 add some more complexity, in combination with Exs. 30-32, they help better illustrate how changing up が and は affects meaning. Even without knowing the extra grammar points or words, the role that these particles play follow what is to be expected from their descriptions. Ex. 56 is talking about noses, and the contrast that follows is still about noses. Ex. 57 is simply about describing elephants, and so the length of their noses and tails aren't being contrasted. In Ex. 58, though, these facts are being contrasted, and the topic is still on elephants, which is why there are three instances of は in the same sentence. Then there's the existence of XがYがZ in Ex. 59. It is possible to have two subjects like this in a Japanese sentence, but in this structure it is best to view [YがZ] as a single predicate unit which is being paired with the exhaustive meaning of が.
60. あれはオオカミではない、狐だよ。
Are wa ōkami de wa nai, kitsune da yo.
That isn't a wolf; it's a fox.
Grammar Note: This example demonstrates how the は in ではない is the contrasting は. Also note how Japanese uses a comma instead of a semi-colon.
61. 運航のダイヤには影響はない。
Unkō no daiya ni wa eikyō wa nai.
There is no effect on the operating schedule.
Sentence Notes: 運航 refers to the operation of aircraft or ships. When referring to the operation of busses or other similar motorized vehicles, it is spelled as 運行. Be careful to pronounce these words with a LHHH (low-high-high-high) intonation as the word unko うんこ with a HLL (high-low-low) intonation means "poop."
Grammar Note: The contrastive は is used heavily with negative sentences. The intent of the speaker is to imply that other scenarios may still be possible but that the one being mentioned is not the case. Meaning, the speaker mentioning the operating schedule isn't implying that there won't be a change in quality of flight. The promise is limited to there being no effect on the timing, which is also why 運航のダイヤに is topicalized.
Another usage of the particle は is to express a bare minimum (saiteigen 最低限)--"at least." This is primarily used with number expressions but it is not limited to them, as is demonstrated by Ex. 59.
62. 少なくとも２に時間はかかります。
Sukunakutomo nijikan wa kakarimasu.
It will take at least two hours.
63. 10人は来ます。
Jūnin wa kimasu.
At least ten people will come.
64 10万円は必要です。
Jūman'en wa hitsuyō desu.
It will need at least 100,00 yen.
65. 牛乳ぐらいは買ってください。
Gyūnyū gurai wa katte kudasai.
At least buy milk, please.
Grammar Note: The particle kurai/gurai くらい・ぐらい is frequently used with this function of the particle は to express "at least." It can actually be inserted similarly to the other example sentences in this section. Its addition creates a greater emphatic tone.
66. 盲腸（虫垂炎）の手術でも1000ドルはかかります。
Mōchō (chūsuien) no shujutsu demo sen-doru wa kakarimasu.
Even appendix (appendicitis) surgery will cost at least a thousand dollars.