"That" -- Required or not?

[Unregistered]

Examples:

1)

"Despite his reassurances to the contrary, I just know that he intends to proceed with pressing charges once that I have left town."

"Despite his reassurances to the contrary, I just know he intends to proceed with pressing charges once I have left town."


2)

"I professed my undying lover for her, and she wept tears of joy. However, what she has yet to discover is that I believed I was talking to her identical twin sister at the time."

"I professed my undying love for her, and she wept tears of joy. However, what she has yet to discover is I believed I was talking to her identical twin sister at the time."


By omitting the "that"s in the examples above, I presume (that) there are no errors being made, and it's just a matter of preference. Why? What dictates whether we should opt for a "that" or not?

Unless, of course, I'm wrong, and by ommitting the "that"s in examples such as those above, I'd be committing a catastrophic grammatical sin.

It's just that I see both of the above put to use each and every day, in newspapers, books, news tv ticker bars, etc., so am curious as to which to use. Thoughts welcomed.

 

[Boadicea]

"That" is optional when the nominal clause functions as the object. It is known as a "complementary node."

So in your first example 'that' can be removed, because the nominal clause (that he intends to proceed with pressing charges once that I have left town) functions as direct object to the verb know. However, it's not possible to remove 'that' in your second example since the clause functions as Complement to the Subject (that I believed I was talking to her identical twin sister at the time) due to the presence of a copular verb (is)