# Obligation

## が必要・必要がある

Means "needed" or "necessary".
が{必要|ひつよう} is used mainly with nouns (can be used with verbs by appending こと before).
{必要|ひつよう}がある is used with verbs.

> [!info] Example
> {今時|いまどき}、{携帯電話|けいたいでんわ}==が必要です==。
> Nowadays, a cell phone is necessary.
> 
> 今日はパン{屋|や}に行く==必要がない==。
> No need to go to the bakery today.

## わけにはいかない

Used with verbs for a meaning of "cannot do" (which cannot be your inability, but an external factor).
Used with verbs in negative form (ない) for a meaning of "cannot be avoided".
Can be used as わけはいかない or わけにはいきません.

> [!info] Example
> {今日|きょう}の{弟|おとうと}の{誕生日|たんじょうび}に行か==ないわけにはいかない==だから、{飲|の}み{会|かい}に行かない。
> There's no way I don't go to my younger brother's birthday today, so I won't go to the afterwork.
> 
> {本当|ほんとう}に飲み会に行く==わけにはいかない==よ。
> There's really no way I can go to the afterwork.

## なくてもいい

Means "don't have to". Used with a verb in the negative form (ない), appending なくてもいい.
Can also be used as なくていい.

> [!info] Example
> 今日はレストランで{手伝|て|つ}わ==なくてもいい==。
> You don't have to help out at the restaurant today (it's okay if you don't help at the restaurant today).

## てからでないと

Means "must first do". The second part becomes possible after the first one.
Used with a verb in て form, with からでないと or からでないければ.

> [!info] Example
> {払|はら}==ってからでないと=={入|はい}るができること。
> You can enter only after paying.

## こと as "should do"

### こと

<div class="usage">
<div class="left">
	<p><span class="box">V (dictionary)</span></p>
	<p><span class="box">V (ない)</span></p>
</div>
	<p class="right">+ こと</p>
</div>

Means "should do". Mostly used to set rules.

> [!info] Example
> ここに{車|くるま}を{止|と}めない==こと==です。
> Don't park your car here.

### ことになっている

This form is used to express rules or expectations.
Used with dictionary (る) and negative (ない) form of verbs.

> [!info] Examples
> {指|ゆび}で食べない==ことになっている==。
> You're not supposed to eat with your fingers.

### ことはない

This has two meanings:
* it is not necessary to
* it never happens

Used with a verb in the dictionary form.

> [!info] Example
> {走|はし}る==ことはない==。まだ{時間|じかん}がある。
> There's no need to run. There's still time.

## 必ず

{必|かなら}ず means certainly, definitely. Expresses an obligation.

> [!info] Example
> 明日の{授業|じゅ|ぎょう}==必ず==来てください。
> Please be sure to attend tomorrow's class.

## べき

### べきだ

Means "should do", "must do". Compared to the [[Obligation - なければ・ないと]] forms and 必ず, it has a nuance of being less universally logical. It is defined by the speaker's own logic.
Used with verbs.
する can be used as するべき or すべき.

> [!info] Example
> {来週|らいしゅう}{試験|しけん}があるので{勉強|べんきょう}す==べきです==。
> There is an exam next week, so I should study.

### べきではない・べきじゃない

The contrary of べきだ is べきではない・べきじゃない.

> [!info] Example
> {泥|どろ}を食べる==べきではない==。
> You should not eat mud.

## はずだ・はずがない

<div class="usage">
<div class="left">
	<p><span class="box">V</span></p>
	<p><span class="box">い-Adj</span></p>
	<p><span class="box">な-Adj + な</span></p>
	<p><span class="box">N + の</span></p>
</div>
	<p class="right">+ はずだ ・ はずがない</p>
</div>

はずだ means "it must/should be", while はずがない means "it cannot be". Has a nuance of being sure that it is something possible (or impossible).

> [!info] Examples
> {彼|かれ}は今日来る==はずだ==。
> He should be coming today.
> 
> そんあ==はずがありません==。
> This cannot be true.