English translation:
It is a fact that ~
There is no doubt that
Structure:
Phrase + (という)のは事実だ
The structure box on the grammar page looks a little weird:
Phrase + (という)のは事実だ
Phrase + だ というのは事実 (だ・です)
Should these both be here? I see that only the first structure example is here on this topic; I’m guessing the だ is specifically needed after nouns?
And what’s the criteria for whether or not という should be included? Is it generally optional?
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Hey 
I have changed the structure a bit, to make it easier to read. 
When it comes to と, だ is optional after noun or な adjective.
(Though in some cases it is more natural to never add だ like といっても)
Generally, という must be used when the phrase before it has one of ending particles like よ、わ、ぜ、etc is used or it is unfinished (食べて). Those two cases imply quotation.
In other cases it is optional, but there are some preferences:
- when you want to emphasize something
- when a clause is long, and you want to make it easier to read
- when you want to put some distance between you and the information (basically, make it more indirect by making a quotation)
You use という.
That is basically it,
I hope it helps,
Cheers 
3 Likes
Thank you for the thorough reply!
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Can こと substitute for の here?
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@ulurujamman
Hey
Good question!
You can substitute の with こと, it will be correct and understandable. However, の is used more often to say that than こと, so I would stick to it.
It is a similar case to のが好き and のが嫌い、ことが好き、ことが嫌い are also used but are less common that の versions.
Though I would say that it is more noticeable with 嫌い・好き than with は事実だ。
I hope it helps,
Cheers!
2 Likes
Thanks for the explanation @mrnoone .
In the example sentence: " 彼が俳優だというのはじじつだ" the version without という is not accepted as a valid answer. According to your explanation of the cases where という is mandatory, it seems to me it doesn’t apply here: the phrase does not end with an ending particule and is not unfinished. Is the use of だ another case where という is mandatory? だのは does not sound very nice, maybe this is the reason?
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It’s because its ending with だ. You can say “彼が俳優のは事実だ”, but, the answer we’re looking for includes that だ, which would need to be omitted for this hypothetical alternate answer to work.
Hope this cleared it up a bit! It’s mostly a quirk of the quiz system rather than some weird grammar shenanigans.
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Also, sorry for the year-old reply. 
Hi, sorry for digging up an old conversation, but I don’t quite understand why this sentence gives me the alt answer without という part then:
It seems to be inconsistent (unless I don’t get some nuance or something).
Hey @electrosuccess !
This seems like an error on our end so we have just fixed it! という needs to be included here! 
Thanks for letting us know about this!
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