Even though adverb もし translates to ”if” in English, and it is usually at the beginning of a sentence just like English “if”, it is not a must in “if” statements. Instead the particles and aux verbs are what really make “if” statements in Japanese.
In the below examples もし is optional, and it is たら that makes this statement an “if” statement:
- (もし)良かったら食事に行きませんか？ -> Why don’t we go for a dinner if it is OK with you
The same goes for other adverbs like 仮に, たとえ.
たら, なら, ば, と
たら, なら, ば and と are all used to construct standard “if A, then B” statements.
- たら is 仮定形 of perfect-tense aux verb た, and follows 連用形 of a verb or aux verb
- なら is 仮定形 of declaration aux verb だ and can follow a noun, nominal clause, verb, adjective
- ば is 接続助詞 and follows 仮定形 of a verb, aux verb, adjective
- と is 接続助詞 and follows 終止形 of a verb, aux verb
Because of the above structural constraints, when to use which depends on the construction of the sentence. For instance after a noun なら is the only option.
- ラーメンなら食べたい -> I want some if it is ramen
- 明日なら時間が有る -> I have time if it is tomorrow
However たら can follow だ, and the resultant だったら is basically the same with なら, except だったら is colloquial.
- これなら良い
- これだったら良い
- It is OK if this is it
- 今時間が無いなら明日でも構わない
- 今時間が無いのだったら明日でも構わない
- Tomorrow is OK if you don’t have time now
- 私ならそうはしない
- 私だったらそうはしない
- I wouldn’t do it if I were you
Generally:
- たら is colloquial, more informal than なら and ば
- ば and と are for more likely suppositions than たら and なら. As a result ば and と are rarely used with もし
- と is usually used when the result is contrasting
- なら is the most hypothetical
The below illustrates what and what are the same, and what doesn’t work:
- You will make it if you send it by express mail
- 速達で送れば間に合う
- 速達で送ったら間に合う
- 速達で送るなら間に合う
- 速達で送ると間に合う -> It is not hypothetical enough, like “Send it by express mail and it is guaranteed to make it”
- What happens if I do this?
- こうしたらどうなる？
- こうするとどうなる？
- こうすればどうなる？-> Less common
- こうしたならどうなる？ -> Not wrong, but したら is much easier to say and universally preferred
- It is OK if you do what you want. Do as you like
- 好きなようにしたら良い
- 好きなようにすれば良い
- 好きなようにすると良い -> Less common
好きなようにするなら良い-> It sounds more like “it is OK as long as you do what you want. Don’t do it unless you do the way you really want to do”
- It is OK for you to come when you want. Come whenever you want
- 来たい時に来たら良い
- 来たい時に来れば良い
- 来たい時に来ると良い -> Less common
来たい時に来るなら良い-> It is too hypothetical. It sounds more like “It is OK as long as you come only when you really want to come. Don’t come unless you really want to come”
- If, when, there is that much, it should be enough
- それだけあったら十分でしょう
- それだけあれば十分でしょう
- それだけあるなら十分でしょう -> It sounds more like “since you have that much, it should be enough”
それだけあると十分でしょう-> Not hypothetical enough
- If you are OK with it, then it is OK. As long as you are OK, it is OK
- あなたが良いならそれで良い
- あなたが良ければそれで良い
- あなたが良いんだったらそれで良い
あなたが良いとそれで良い-> Not hypothetical enough
- If he is going, then I am going too
- 彼が行くなら私も行く
- 彼が行くんだったら私も行く (行くん is a colloquial alteration of 行くの)
彼が行けば私も行く-> It is not hypothetical enough, like “when he goes I go too”彼が行くと私も行く-> It is not hypothetical enough, like “he goes then I go too”
Highly unlikely or impossible suppositions
For highly unlikely or impossible suppositions, たら will be the first choice, even in writing.
As mentioned above, たら is 仮定形 of the aux verb of past/perfect tense た, and the effect is somewhat similar to the subjective moods in English.
- It would be wonderful if I could fly
- もし空を飛べたらいいだろうな
- もし空を飛べればいいだろうな -> Less common
- もし空を飛べたならいいだろうな -> た is an aux verb of past/perfect tense. Less common
もし空を飛べるならいいだろうな-> Not hypothetical enoughもし空を飛べるといいだろうな-> Not hypothetical enough
たらば, ならば
Technically ば can follow both たら and なら. ならば is relatively common but sounds literary, and たらば is not wrong but hardly used, probably because it is mouthful.
- 彼なら(ば)出来るだろう -> It can be done if he does it
そうしたらば
ては, たら
“It is not OK if you do…” statements, which are often translated “you can/should not do…” in English, are constructed with ては or たら. ては is slightly literary and たら is colloquial.
ては(では) becomes ちゃ(じゃ) in informal conversations.
- そんな事をしてはいけない
- そんな事をしちゃいけない
- そんな事をしたらいけない
- It’s not OK if you do something like that. You shouldn’t to that
- そんなに酒を飲んじゃいけない
- そんなに酒を飲んではいけない
- It’s not OK for you to drink that much alcohol. You shouldn’t drink that much
では
では is constructed with [declaration aux verb だ + 接続助詞は] and is used only when the result is undesirable.
- このままでは不味い -> It will be a problem if this continues
- このままでは間に合わない -> We won’t meet the deadline (if we continue) at this rate
- 彼一人では無理だろう -> He won’t make it if he is alone, has no help