How to analyze たこともある?


In Tobira chapter 11 grammar, one of the examples is
奈良は京都と並んで、古い歴史のある町で、日本の首都だったこともある。

I don't seem to find any information about たこともある on the entire web.

I understand there is no difference between (verb casual non
past)+こともある/ことがある, which means sometimes or there are times when.

I was warned not to confuse with the construction (verb た-form)+ことがある, which
means to have done something before. Is たことがある the same as た+こともある?




I think you should stick just to ことがある. (In this sense, yes たことがある is
た＋ことがある).

ことがある means _did something before_ as you understand. More abstractly, it
expresses a past experience.

  * 私はアメリカに行ったことがある I've been to the US.

Whether it translates to present perfect or past tense in English depends on
the meaning.

  * 奈良は日本の首都だったことがある

can be translated _Nara **was once** the capital of Japan_. Here it in a sense
express an 'experience' of the city Nara.

こともある could be _Nara was also ..._ , but it should be clearer to say _There
was also a time when Nara was the capital of Japan_.

