Consider the following use case:
- Please check the username and password are correct.
- Please check that the username and password are correct.
In this case, I would say that that is required because it feels more natural to me and so the flow is better. However, is the lack of that wrong in this case?
The question boils down to: when is that optional? See here. A quick summary:
- That is optional if the pronoun is the object.
- That is required if the pronoun is the subject.
I think that we fall into the second case: that is required because the relative pronoun is the subject. But I'm not sure if I'm interpreting these rules correctly. Can someone please advise?