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When is it recommended to use としたら in place of simply たら? It seems that in
many cases たら can serve the role of "if it you were..." so in what places do
we need to use としたら? For example,

> もし今東京に住んでいたらコロナに巻き込まれているんだけどね

vs

> もし今東京に住んでいるとしたらコロナに巻き込まれているんだけどね

What is the difference here, and more generally speaking. Also it seems that
perhaps other conditionals could be used here so I wonder about that too. For
instance.

> もし山田さんが来てなければこのテーブル持ち上げられません

vs

> もし山田さんが来てないとしたらこのテーブル持ち上げられません

PS: If relevant, what is the difference between these conditionals and 仮に
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2021-04-19T06:41:24.133
86221
2021-05-10T05:38:53.787
2021-04-19T07:38:11.480
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question
grammar conditionals comparison
When to use としたら instead of たら for conditionals
The first sentence in the first pair would most likely be interpreted as an
unreal conditional about either the speaker or someone else, as you intended.

> もし今東京に住んでいたらコロナに巻き込まれているんだけどね  
> If we/you/they were living in Tokyo now, we/you/they would be caught up in
> the coronavirus pandemic.

In the situation of the second sentence, on the other hand, the speaker is
necessarily talking about someone other than himself (or the listener). He
doesn’t know for sure whether that person is living in Tokyo. She might be. If
she is indeed living in Tokyo, she must be caught up in the pandemic.

> もし今東京に住んでいるとしたらコロナに巻き込まれているんだけどね  
> Supposing they are living in Tokyo now, they must be caught up in the
> coronavirus pandemic (, but I’m not sure).

The uncertainty in the last part is due to んだけどね, not because of としたら.

Actually, this interpretation is not completely impossible from the first
sentence, though it’s not very likely. としたら makes sure the sentence is
understood as a supposition about something the speaker is not sure about.

The same logic works for the second pair. The first sentence is a simple
conditional.

> もし山田さんが来てなければこのテーブル持ち上げられません  
> If Yamada-san hasn’t come, we cannot lift this table.

In the situation of the second sentence, the speaker is somewhere other than
where Yamada-san is expected and is not sure whether he has reached there yet.
Yet that place has to be one for which the use of 来る is logical and the table
is where the speaker is (because of この).

> もし山田さんが来てないとしたらこのテーブル持ち上げられません  
> Supposing Yamada-san hasn’t arrived there, we cannot lift this table.

I don’t know how but the decision of whether or not to lift the table must be
somehow influenced by the presence or absence of Yamada-san in some other
place.
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2021-05-01T03:20:40.977
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2021-05-10T05:38:53.787
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answer
For simple conditionals ("if"), use ~たら.

To talk about an imaginary situation ("imagine that"~, "let's suppose that~",
"if you were to~", etc.) use ~としたら:

> タイムマシーンがあるとしたら、どの時代に行ってみたい？

> Imagine that you have a time machine, what epoch would you like to go to?
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2021-05-08T23:58:16.450
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answer