grammar - The different usages of ことがある

If I understand correctly, the main usages of ことがある seem to be the following:

• Verb(plain)+ことがある: There are times when (I)


• Verb(past)+ことがある: (I) have experienced (something) before

But after this question, I'm starting to wonder when ことがある means "there is a thing/there are things" instead of "there are times when".

When looking through Space ALC and Google searches, I'm thinking ～たいことがある might mean "there's a thing I want to (do)" and ～たくなることがある "there are times when I want to (do)" based on the way they're used, but I can't be sure.

書きたくなることがあります
"there are times I want to write" (?)

書きたいことがあります
"there are things I want to write" (?)

What are the different usages of ことがある? When does ことがある mean "there are things" rather than "there are times when" and how can they be told apart?

Answer

The clause used in ...ことがある is structurally ambiguous between an appositive clause and a relative clause.

書きたくなることがあります

1. As appositive clause
　書きたくなる 'I become tempted to write something' is the content of the formal noun こと 'occasion'
　'There are occasions that I become tempted to write something.'
2. As relative clause
　The こと '(factual) thing' is the missing object of the relative clause 書きたくなる 'I become tempted to write'
　'There are things that I become tempted to write.'

It is just as the same in English. Depending on whether you interpret the English write in:

　There are occasions that I become tempted to write

as intransitive or transitive, you can interpret the clause as appositive or relative, and will get the two meanings.