Gradual process 〜ていく、〜てくる (〜teiku, 〜tekuru) + Beforehand 〜ておく (〜teoku)

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にほんごがわかってきた!
Nihongo ga wakatte kita!
I am starting to understand Japanese!

Gradual process

The verbs いく and くる attached to other verbs can express the gradual process of something.
〜ていく will focus on the starting point, while 〜てくる will focus on the end point.

Take these two sentences for instance:

A gaggle of geese flew away.
ガチョウのむれはとんでいった
Gachou no mure wa tonde itta.

If the geese flew towards you, you can switch the verb to くる.

A gaggle of geese flew in.
ガチョウのむれはとんできた
Gachou no mure wa tonde kita.

These sentences can also be translated as 'the geese went away flying' and 'the geese came flying in'.
It shows a process of the geese flying away or flying in.

You can also use these expressions with time. Let's say that you have decided to learn 10 kanji a day, you can say....

From now on, everyday, I am going to remember 10 kanji.
これからまいにち、あたらしいかんじをじゅうまいおぼえていくつもりです。
Korekara mainichi, atarashii kanji o juu mai oboeteiku tsumori desu.

This concept might be a little bit hard to grasp, but it will make sense to you in time. 

This expression is often used when you are instructing others to do something. 

So, let's start first by doing some light stretches.
それでは、まずはかるいストレッチをしていきましょう
Sorede wa, mazu wa karui sutorecchi o shiteikimashou.

In this sense, it is marking the starting point of something that will be going on for a while.

On the other hand, 〜てくる adds the nuance that an action or a state is getting close to you in time. It means that you are looking back at the continuation of an action or state from a moment in the past up to the current point in time.

We've done light stretches up to this point.
ここまではかるいストレッチをしてきました
Koko made wa karui sutorecchi o shitekimashita.

If you are still mixed up about these expressions, do not hesitate to contact me!

You will also see these expressions being written in hiragana
The kanji for いく is 行く and for くる is 来る, but since the meaning is not literal in this case, we write these in hiragana.

To keep writing out (something)
かきだしていく
Kakidashiteiku

To become more visible
みえてくる
Mietekuru

With adjectives + なっていく / なってくる

When you describe a change of state, you will often combine adjectives with the verb なる and plugging in いく or くる.

To become quieter
しずかになっていく
Shizuka ni natteiku

Do not forget that with い-adjectives, it takes く with なる!

To become happier
うれしくなってくる
Ureshiku nattekuru

Some verbs only work with 〜てくる. This is the case for perception verbs, such as きこえる (to hear), においがする (to smell), and みえる (to see), which are verbs that convey your physical experience.

When these verbs are combined with 〜てくる, it expresses the gradual process of perceiving something.

I started to hear the sounds of birds.
とりのおとがきこえてきた
Tori no oto ga kikoete kita.

If you only say とりのおとがきこえた, it only expresses that you heard the sounds of birds, thus not making it dynamic. The sentence can also be translated as 'sounds of birds came in'.

It started to smell curry.
カレーのにおいがしてきた
Karee no nioi ga shite kita.

You can view this sentence as the smell left the kitchen, floated in the air and reached your senses.

The island finally came into view!
ついにしまがみえてきたぞ!
Tsuini shima ga miete kita zo!

In this sentence, even in English, it gives something more to the sentence rather than just stating you finally saw the island.

With potential verbs

Another type of verbs that only requires 〜てくる is potential verbs, such as your ability of doing something, like わかる (to understand) and できる (to be able to do). If you pair these with 〜てくる, it shows the process of obtaining a result.

I'm starting to understand Japanese.
にほんごがわかってきた
Nihongo ga wakatte kita.

〜てくる can also be used with the potential form of verbs.

I'm starting to be able to read kanji.
かんじをよめてきた
Kanji o yomete kita.

In some circumstances, 〜てくる will change a verb into another.

とる - to take
とってくる - to fetch
もつ - to have (physically in your hands)
もってくる - to bring
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Beforehand

The form 〜ておく signifies that you are doing something in advance in order to get it out of the way or to put it away in your mind.

おく is a verb in itself meaning 'to put'. Attached to verbs, it has the connotation of doing something now for future convenience. 

Let's say that you are taking a Japanese class and the teacher tells you what you will learn next lesson. At home, you tell yourself that you will read this chapter in advance for next class. You can then say....

I will read the lesson on Kanji (in advance).
かんじのレッシュンをよんでおく
Kanji no resshun o yonde oku.

This expression also implies that you are doing something now to achieve a better result later, e.i you eat lunch now so your belly won't growl later, or you are training now to gain muscles, or you read a chapter in advance to be fully prepared for a class.

This expression can also mean that you are taking care of something at hand or even leaving something as is.

Again, this construction uses the 〜て form of verbs.
In casual speech, this expression will sometimes be shortened into 〜とく or 〜どく.

みる -- みて -- みておく -- みとく
よむ -- よんで -- よんでおく -- よんどく

To do something beforehand

I am going to Japan next year, so I am studying right now.
らいねんにほんにいくので、べんきょうしておく
Rainen nihon ni iku node, benkyou shite oku.

Here, it means that you are studying in preparation for your trip. In this sentence, it is clear that what you say is that you are studying because you are going to Japan next year. But the meaning does not have to be so clear.

Let's say that you are still studying Japanese because you want to, and that you have the time to study right now, you can still use おく.

While I have the time, I should get some studying done.
いまのうちに、べんきょうしておこう
Ima no uchi ni, benkyou shite okou.

In this case, there is no certainty that you will have time later on to study, so you are doing it now.

Now, let's see the nuance.

Then, I'll make the reservation!
じゃ、わたしがよやくするよ!
じゃ、わたしがよやくしておく!

Here, you can say both in the situation where you and your friends want to go to a restaurant and you will make reservation. The first sentence only means that you will make the reservation. On the other hand, the second option, with おく, it implies the meaning of 'I've got this' and that the reservation will be taken care of well before time.

You can use the expression おく when requesting or suggesting someone else take action in advance.

I'm sorry if it is a bad moment, but could you make the reservation for us?
わるいんだけど、よやくしておいてくれないかな?
Waruin da kedo, yoyaku shite oite kurenai kana?

In this example, you could have only ask if the person could make the reservation without using おく, but when おく is added, it means that the person does not have to hurry to make the reservation, as long as the reservation is done. It is, thus, less direct.

For doing something now

You can also use おく to describe an action you are doing now as a temporary or tentative solution.

For instance, let's say you did make a reservation and you have reached the restaurant, but one friend is missing. The server arrives at your table.

What do we do? Do we order something to get started?
どうしよ?とりあえず、なんかたのんでおく
Dou shiyo? Toriaezu, nanka tanonde oku?

It is impolite in Japan to start ordering if everyone hasn't shown up yet. In this context, it shows that you are aware that what you order might not be what everyone wants to order, but you are just ordering to get started. とりあえず (for the time being) will often be paired with おく in this matter.

Another example is the uncertainty. Let's say your friend is taking a shower, but forgot to bring a towel with them. You bring the towel to them, but you are unsure where to put it.

I'll put it here, okay?
ここにおいておくね!
Koko ni oite oku ne!

Yes, you can double up the verb! In this case, it shows that you don't know where the best place is to put the towel, but you put it somewhere anyway.

It can also work in situations where we need to end something, even though it isn't the right time to finish it.

It is already this time... Well, let's wrap up the class here (I will finish the class here.)
もうこんなじかん。。。じゃ、じゅうぎょうをおわっておく
Mou konna jikan... ja, juugyou o owatte oku.

It means that you leave it in suspense for now and will start back where you finished.

For leaving something as is

You can use おく to imply that you leave something as is. It is often used in situation where the action doesn't seem purposeful.

I parked my bike in front of the store, and it got stolen.
みせのまえにじてんしゃをとめておいたら、ぬすまれた。
Mise no mae ni jitensha o tomete oitara, nusumareta.

In this example, you left your bike as is (without the lock or anything) and did not park it there to get it stolen, or at least, you didn't expect it to get stolen there.

ら in おいたら means 'after', 'after I parked my bike in front of the store, it got stolen.

In this situation, this expression is paired well with a phrase that means 'to leave something' 〜のままにしておく.

Let's take the example of the bike that was stolen. Let's say you park your bike without a lock and your friend notices it.

I think it is dangerous if you leave it like that.
それ、そのままにしておくのは、あぶないとおもうよ。
Sore, sono mama ni shite oku no wa, abunai to omou yo.

Nuances

You probably see now that we can nuance things with this sentence structure.

Take these 2 sentences for instance with the verb つけっぱなしにする (to leave something on):

I left the lights on.
でんきをつけっぱなしにした。
Denki o tsukeppanashi ni shita.

でんきをつけっぱなしにしておいた。
Denki o tsukeppanashi ni shite oita.

Can you spot the nuance?

In the first example, it appears that you left the lights on on purpose. 
In the second example, it implies that you left the lights on and your forgot to turn them off.

This is why some of my former students were asking me why in anime they seemed to be saying things totally different from what the subtitles meant. Sometimes in English, you cannot convey as much meaning, unless you add something to the sentence.

If, for instance, you would have to translate this sentence でんきをつけっぱなしにしておいた, you would have to translate it as 'I left the lights on and I forgot to turn them off', even though the verb 'to forget' is not part of the sentence.

Here's another example:

I understand. I'll return them for you.
わかりました。へんきゃくしておきますね。
Wakarimashita. Henkyaku shite okimasu ne.

In this context, you are telling the customer that you will take care of something for them. It shifts the responsibility from them to you.

Letting someone continue to do something

The causative form, combined with おく (させておく) gives the meaning that you are letting someone continuing an action.

I should let him sleep.
このままねかせておいてあげよう。
Kono mama nekasete oite ageyou.

A famous expression is used with this structure.

Let's play cat and mouse with him a little bit longer.
あいつはもうすこしおよがせておこう
Aitsu wa mou sukoshi oyogasete okou.

およがせておく literally means 'letting someone keep swimming' which mean figuratively that you're playing cat and mouse with the person.

〜ておく vs. 〜てある

Like 〜ておく, 〜てある can show someone doing something in preparation for the future. However, the focus is different.

〜ておく is person-centred, whereas 〜てある is object-centred.

Breakfast is already made, okay?
あさごはん、つくっておいたからね!(I prepared breakfast)
あさごはん、つくってあるからね!(Breakfast was made)

In the first sentence, you put the focus on you having made breakfast.
In the second sentence, it is implied you made it, but it is now in the background.
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You have completed lesson 25!
レッシュン25ができた!

Seems to feel like 〜がる (〜garu) + Explanatory feel 〜んです、〜んだ (〜ndesu, 〜nda) + Want something to happen 〜てほしい (〜te hoshii)

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まんがをよめたいんだ。
Manga o yometainda.
It's because I want to be able to read manga.

Seems to feel like

We saw in an earlier lesson how to say it seems like, sounds like or looks like with adjectives. 
There is another form we haven't seen yet, and it is い-adjectives + がる. This construction is used if you want to say that somebody seems to be in a certain state. This is you stating that you think someone is experiencing something, not stating a fact, so be careful to not mix this form with 〜そう or みたい.

To describe how we feel, we use adjectives to do so. However, to describe how someone else might feel, using the adjective is not enough. That is when がる comes to your aid. Attached to an adjective, it means 'showing signs of'. While うれしい means 'happy', うれしがる will mean 'show signs of being happy'.

You can use this expression to state your thoughts that a person is happy based on physical clues, such as facial expressions, but you can also use it to state that you are not sure, something like 'this person is pretending to be...'

To use this expression with い-adjectives, simply drop the last い and add がる. Simple!

うれし + がる

Be aware that once you attach がる to an adjective, it no longer acts as an adjective, but as a verb.
It is mostly used with adjectives that will express a subjective thought or feeling. Since がる is used to describe how a person appears to be, you will most often find it in the present or past continuous form. がる acts as a godan verb.

Shaoran seems to be jealous.
シャオランはうらやましがっている
Shaoran wa urayamashigatteiru.

Shaoran seemed to be jealous when I won.
わたしがかったとき、シャオランはうらやましがっていた
Watashi ga katta toki, Shaoran wa urayamashigatteita.

がる is not only used in the present or past continuous forms however. To talk about a hypothetical situation, you will have to use it in the future form or simple present form.

If my brother moves out of the house, my mother will feel lonely.
おにいちゃんがいえをでたらおかあさんがさびしがる
Oniichan ga ie o detara okaasan ga sabishigaru.

While this expression is mostly used to describe how other people might feel like, you can use it to describe your own behaviour and how your behaviour affects others.

When I show that I want snacks, my little sister always shares hers with me.
ぼくがおかしをほしがると、いもうとはいつもわけてくれる。
Boku ga okashi o hoshigaru to, imouto wa itsumo wakete kureru.

The main focus of the sentence is your little sister and how she always shares with you. We use がる to alert your little sister your need for snacks.

You might have notice that the particle used here is を and not が. Typically, with ほしい we use が, but since there is がる we will use を. Remember that adjectives with がる act as verbs and not adjectives! This is why we use を instead.

I am jealous of Shaoran.
ぼくはシャオランうらやましい。
Boku wa Shaoran ga urayamashii.

Shaoran is jealous of me.
シャオランはぼくうらやましがっている
Shaoran wa boku o urayamashigatteiru.

がり for nouns

If we use がる in its stem form がり, we can turn adjectives into nouns, such as 'a person who show signs of'.

さびしがりひと - a lonely person (a person who shows signs of being lonely)
こわがりねこ - a cat who shows signs of being scared (a scared cat)

Since we are on the subject, there is a way to transform adjectives into nouns. Adding さ turns an adjective into a noun and gives it the nuance that the noun is objective and measurable. It can be the equivalent of 'ness' in English, like 'goodness', 'freshness', 'liveliness'...

There is a counterpart of this which is み that will turn some adjectives into nouns that is not measurable.

たかい -- たかさ
High, expensive -- height

べんりな -- べんりさ
Practical -- practicality

You can combine さ with other suffixes, like 〜たい, 〜やすい, 〜にくい, 〜らしい, 〜づらい and 〜っぽい.

つかう -- つかいやすい -- つかいやすさ
To use -- easy to use -- usability

おとこ -- おとこらしい -- おとこらしさ
Man -- manly -- masculinity

いく -- いきたい -- いきたさ
To go -- want to go -- eagerness to go

The fundamental use of 〜さ nouns is to express amounts that are objectively measurable.

Before going to the airport, I measured the weight of my luggage.
くうこうにいくまえいに、カバンのおもさをはかりました。
Kuukou ni iku mae ni, kaban no omosa o hakarimashita.

Check the depth of the swimming pool before you go in.
プールのふかさをかくにんしてからはいろう。
Puuru no fukasa o kakunin shite kara hairou.

You can use さ to express subjective qualities as objective truths, such as やさしい, むずかしい and おもしろい, even though these might feel subjective in nature. The add of さ creates a sense that the quality is objective or is an external truth, unlike み, which suggests a more personal, internally felt quality. We will see み below.

I can imagine the difficulty of the test.
テストのむずかしさを よそうする。
Tesuto no muzukashisa o yosou suru.

Your kindness means a lot to me.
あなたのやさしさはわたしにとってたいせつなものです。
Anata no yasashisa wa watashi ni totte taisetsuna mono desu.

さ in opposite pairs (like big and small, tall and short) tend to have opposite meaning.
For instance, おおきさ represents size, but ちいささ can only means 'smallness' and do not represent size like おおきさ does. The same applies to はやさ when we speak about speed, but おそさ can only mean 'slowness'. You have to be careful with that. 

Let's see the difference between さ and み. 

That movie is missing an element that intrigues me.
あのえいがはおもしろみにかけている。
Ano eiga wa omoshiromi ni kaketeiru.

That movie is missing an interesting element (to everyone).
あのえいがはおもしろさにかけている。
Ano eiga wa omoshirosa ni kaketeiru.

In the first sentence, it is clear that the missing element is something that is felt only by the speaker, whereas in the second example, this missing interesting element is felt by everyone and everyone would agree that the movie is missing something interesting.

Unlike さ, み can only be paired with limited adjectives. As mentioned, it gives more of a personal or internal feeling to things. It gives a feeling that you are treating the noun as something subjective and personal.

Take these two examples:

How sweet do you want your tea? (How do you like the tea's sweetness)
おちゃのあまさはどうしますか?
Ocha no amasa wa dou shimasu ka?

As summer turns into fall, the special quality of sweetness of these tomatoes comes through.
なつからあきにかけて、このトマトにはとくべつなあまみがでてくる。
Natsu kara aki ni kakete, kono tomato ni wa tokubetsuna amami ga dete kuru.

In the first sentence, the sweetness of your tea is objective, because you decide how sweet you want your tea. In the second example, the sweetness of the tomato is subjective, because that sweetness could be different for somebody else.

み can also be attached to adjectives to give a metaphorical sense to things.

There is some heaviness in that movie.
このえいがにはおもみがある。
Kono eiga ni wa omomi ga aru.

There is warmth in Meilin (Meilin is a warm person).
メイリンはあたたかみがある。
Meirin wa atatakami ga aru.

み often has a verb equivalent that ends in む.

たのしい -- たのしむ -- たのしみ
Fun -- to be fun -- enjoyment

かなしい -- かなしむ -- かなしみ
Sad -- to be sad -- sadness

いたい -- いたむ -- いたみ
Painful -- to feel pain -- pain

くるしい -- くるしむ -- くるしみ
Suffering -- to suffer -- anguish

Emotion adjectives, such as さびしい and うれしい, do not have a verb counterpart, thus they cannot get the み suffix. However, languages change over time, and young people are starting to use み for these adjectives.

Finally, み is often used with flavours. 

からみ -- spiciness
あまみ -- sweetness
すっぱみ -- sourness
しょっぱみ -- saltiness
うまみ -- flavourness
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Explanatory feeling

〜んです and 〜んだ are used to add an explanatory feeling to a sentence. It provides information in order to fill in the gap of understanding.

〜んです with its variants 〜んだ, 〜のです and 〜のだ usually come at the end of a sentence. It is there to provide more information to fill in the gap, thus you will often use these to explain something or to resolve an understanding.

Let's say that someone holds Canadian-American citizenship even though their parents are both Canadian. People want to know why this person also holds American citizenship.

(It's because) I was born in the US.
(じつは)アメリカにうまれたんだ
(Jitsu wa) Amerika ni umaretanda.

じつは means 'the truth is'. You can still use じつは and not use 〜んだ, but it may sound less natural and might come off as a random statement. Adding 〜んだ creates a natural flow for you to complete the context by providing an explanation for why you hold American citizenship, since people are really wondering why you would hold this citizenship if your parents are both Canadian.

〜んだ and 〜んです are actually shorter versions of 〜のだ and 〜のです. It is like contractions, if you may.

You can use pretty much any form of verbs with these, present form, passive form, potential form, negative form... 

However, the command form of the volition form cannot have 〜んだ as they don't make sense in an explanation form.

X べんきょうしろんだ。

Also, it doesn't work neither with the 〜ます form.

X べんきょうしますんだ。

With い-adjectives

With い-adjectives, we only need to add 〜んだ (or its variants).

It is sad.
かなしいんだ。
Kanashiinda.

It isn't sad.
かなしくないんだ。
Kanashikunainda.

It was sad.
かなしかったんだ。
Kanashikattanda.

It wasn't sad.
かなしくなかったんだ。
Kanashikunakattanda.

です should never be used with this form.

X かなしいですんだ。

With nouns and な-adjectives

With nouns, you need to add な.

I am a vegetarian.
ベジタリアンなんだ。
Bejitarian nanda.

With な-adjectives, they will retain their な.

It's simple.
かんたんなんだ。
Kantan nanda.

For the negative and the past, we only have to conjugate the verb.

I was a vegetarian.
ベジタリアンだったんだ。
Bejitarian dattanda.

It isn't simple.
かんたんじゃないんだ。
Kantan janainda.

To explain misunderstandings

〜んだ can be expressed to resolve misunderstandings. 

Let's say that your sister accuses you to have eaten her share of pudding. You can defend yourself by using this form.

No, you're wrong, it is mum who ate it.
ちがうよ、おかあさんがたべたんだよ。
Chigau yo, okaasan ga tabetanda yo.

ちがう is a verb that means 'to be wrong' or 'to be different'.

For realisation

There is another context where we use this form, and it is for realisation. 〜んだ indicates that you were not previously aware of something and you suddenly realised it.

Let's say that one of your co-workers got promoted and you didn't know. You are suddenly aware of their promotion.

You got promoted. Congratulations!
しょうしんしたんだ。おめでとう!
Shoushin shitanda. Omedetou!

Aah, you graduated, right? Congrats.
ああ、そつぎょうしたんだね。おめでとう。
Aa, sotsugyou shitanda ne. Omedetou.

To be more polite, you can use 〜んです. However, in certain situations, 〜んだ is better than 〜んです. This is the case for when you are talking to yourself. 〜んだ is more self-directed.

I see, so he got dumped...
そっか、フラれちゃったんだ。。。
Sokka, furarechattanda...

の and 〜んですか for seeking information

〜んだ can be used in a question to inquire about an information. In real-life conversations, の and んです will be the most used.

Something happened?
なにかあったんですか?
Nanika attandesu ka?

なにかあったの?
Nanika atta no? (more casual)

What happened?
どうしたんですか?
Doushitandesu ka?

どうしたの?
Doushita no?

〜んだ to introduce a new topic

〜んだ is also used to add something to fill in the gap, even when something was not raised in the conversation. 

Let's say that your friend arranged to meet you, but you unfortunately cannot show up today, because you caught a cold. It wasn't planned, and your friend wonders why you cannot meet with them.

Sorry, I cannot meet you today. I caught a cold.
ごめんね、きょうはあえない。かぜひいちゃったんだよ。
Gomen ne, kyou wa aenai. Kaze hiichattanda yo.

I see, it's too bad. Well, rest well!
そっか、ざんねんだね。じゃ、よくやすんでね!
Sokka, zannen da ne. Ja, yoku yasunde ne!

The use of なんて

なんて is a word that will put stress on some words. It doesn't really have an explanatory feel, but I wasn't sure where to teach this word in my lessons. The word なんて means something like 'such as' 'things like' and could act as being more explanatory.

VERB (infinitive) + なんて
NOUN + なんて
い-ADJ + なんて
な-ADJ + なんて

Who would have thought things would turn out this way?
こんなことになるなんて、だれがよそうしたでしょう?
Konna koto ni naru nante, dare ga yosou shita deshou?

I think there is no such thing as a bomb in the building
おそらくこのビルにはばくだんなんてしかけられてないよ。
Osoraku kono biru ni wa bakudan nante shikakeraretenai yo.

I don't have anything like secrets that cannot come out.
これだけはそとにだせないひみつなんてものはないんだ。
Kore dake wa soto ni dasenai himitsu nante mono wa nainda.

Sometimes, you will hear なんか, which can mean 'like', and it is used exactly like in English.

When I went to work, like, I saw a strange person on the way.
しごとにいったとき、なんか、へんなひとをみたの。
Shigoto ni itta toki, nanka, henna hito o mita no.
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Want something to happen

We both learned how to say 'I want to do something' with 〜たい attached to verbs and how to say 'I want something' with ほしいです . In the lesson, we learned that ほしいです was only with nouns. But there is actually a form that combine ほしい with verbs. This form is used when we want someone to do something or that we wish something to happen.

We will use the 〜て form of verbs + ほしい. 

Let's say that your lover never does chores around the house and you want them to vacuum from time to time.

I want my lover to vacuum.
そうじきをかけてほしい
Soujiki o kakete hoshii.

Just like in English when you say 'I want you to do something', 〜てほしい will convey the same message. It cannot be used to make a request, since it is pretty direct, so this sentence structure can sound rude. そうじきをかけてください sounds better when requesting someone to do something.

〜てほしい can also means that you want something to happen.
Let's say you are in a class and the class is boring. You wish for it to end quick.

I want it to end quick...
はやくおわってほしい
Hayaku owatte hoshii.

This is different from the 〜たい pattern. Let's see the difference.

はやくクラスをおわりたい。
Hayaku kurasu o owaritai.

はやくクラスがおわってほしい。
Hayaku kurasu ga owatte hoshii.

In the first sentence, there is an indication that you want to end the class. 
This is apparent because 〜たい and the particle を is used. 
In this case, you are making the action to end the class quickly.

In the second example, you want the class to end. This is apparent because of the use of 〜てほしい and the particle が. You want the class to end, not you want to end the class. See the nuance?

In the examples above, the subject or object was omitted because often in Japanese, if the context is clear, we can drop it altogether. 
In the case that the subject is not clear, you will have to add it.

In the example of そうじきをかけてほしい, if you say it to your lover's face, 'you' will be omitted, because it is clear who you want to be vacuuming more. But let's say it comes up in a conversation and you tell your friend you want your boyfriend to clean more. You will use this pattern:

〜に〜てほしい

I want my boyfriend to vacuum.
かれしそうじきをかけてほしい
Kareshi ni soujiki o kakete hoshii.

In this case, the particle に acts like a pin. You pin down who you want to vacuum.

If you want to say 'I also want my boyfriend to vacuum', you can use も either alone or with に.

かれしにもそうじきをかけてほしい
Kaeshi ni mo soujiki o kakete hoshii.

For non-living things, using が is more appropriate than using に.

I want snow to fall.
ゆきがふってほしい
Yuki ga futte hoshii.

In some cases, however, に can be used if you want a specific type of snow to fall.

I want fluffy snow to fall.
ふわふわのゆきにふってほしい
Fuwafuwa no yuki ni futte hoshii.

I want this song to sell well.
このきょくに (が) うれてほしい。
Kono kyoku ni (ga) urete hoshii.

In this case, both particles could work, as it is this song in particular you want to sell well.

For the past tense, simply conjugate ほしい.

I wanted you to vacuum.
そうじきをかけてほしかったです
Soujiki o kakete hoshikatta desu.

For not wanting someone to do something

〜てほしくない is used to say that you don't want someone to do something.

I don't want you to say things like that.
そういうことはいってほしくない
Sou iu koto wa itte hoshikunai.

It also works for command if you use:

I want you to not say stuff like that.
そういうことはいわないでほしい
Sou iu koto wa iwanaide hoshii.

For asking 'do you want me to...'

To say you want to study with someone, you would say いっしょにべんきょうしてほしい. But with a raising intonation, you can ask 'do you want me to study with you?'

いっしょにべんきょうしてほしい?
Issho ni benkyou shite hoshii?

Unless you are close to the person, it is best to avoid this construction, since it can sound a bit arrogant. 

Asking for permission to do something

The causative form can be used to ask for permission to do something if you add ほしい to させて. 

I want you to let me study abroad.
りゅうがくさせてほしい
Ryuugaku sasete hoshii.

I want you to let me go to the US.
アメリカにいかせてほしい
Amerika ni ikasete hoshii.

Depending on the context, させてほしい could also means that you want someone to force (or allow) someone else to do something.
For instance, if you want your spouse to make sure the children are fed by 6 o'clock, you can say:

I want you to feed (the kids) by 6 o'clock.
ろくじまでにゆうごはんをたべさせてほしい
Roku ji made ni yuugohan o tabesasetehoshii.

〜てほしがる for someone else's desires

You remember がる? It works the same here.
While 〜ほしい is used to express your own desires, adding がる will shift the focus on to someone else.

The kids always want me to play with them.
こどもたち、ずっとあそんでほしがるんだよ。
Kodomotachi, zutto asonde hoshi garunda yo.

The kid wants me to buy him candy.
こどもがおかしをかってほしがる。
Kodomo ga okashi wo katte hoshi garu.

Making more polite requests

You can actually use 〜てほしい to make requests, but we will usually make it softer by adding other elements. One of them is the 〜んだ or 〜んです to be more polite. This will give an explanation for the request. We will also add が or けど to set it in the background and adding a phrase like おねがいできる, to check if it is okay to make the request. Another way is to use かな to imply uncertainty or simply use 〜てもいい to give the chance to the person to say no.

I want you to clean your room, can you do this favour for me?
へやをそうじしてほしいんだけど、おねがいできるかな?
Heya o souji shite hoshiinda kedo, onegai dekiru kana?

I want you to review this document, if I can trouble you with this favour.
このしりょうをかくにんしてほしいんですが、おねがいしてもいいですか?
Kono shiryou o kakunin shite hoshiindesu ga, onegai shite mo ii desu ka?

〜てほしい is still a direct way to request things, so if you want to sound more appreciative, you can say 〜てもらいたい instead.

このしりょうをかくにんしてもらいたいんですが、おねがいしてもいいですか?
Kono shiryou o kakunin shitemoraitaindesu ga, onegai shite mo ii desu ka?

〜てもらいたい is actually 〜てもらう which means that you receive a favour from someone. This form is more polite than 〜てほしい, because it shows that you are aware that you are asking for a favour.

If you are talking to someone who is higher up socially, you use 〜ていただきたい. For instance, if you are talking to the president of your company:

Would it be possible for you to review these documents?
このしりょうをかくにんしていただきたいんですが、おねがいしてもよろしいでしょうか?
Kono shiryou o kakunin shite itadakitaindesu ga, onegai shite yoroshii deshou ka?

As you can see, sentences become longer and longer the more polite you are.

おねがいしてもいいです becomes おねがいしてもよろしいでしょう in high formal speech.
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You have completed lesson 26!
レッシュン26ができた!