'I'm sure your friends will likely call you on your birthday.' Is "that" required?

Question

Could someone please help me.

I was wondering if I have to use "that" in the following sentence:

I'm sure your friends will likely call you on your birthday.

Should there be a "that" between sure and friends?

Thank you.

Leaving it out is more natural in speech, but in both speech and writing, either way is OK. — ab2, Jan 18 '16 at 00:49
@deadrat I posted another duplicate question. I think it is better as the omitted that is not a relative pronoun. :-) — , Jan 18 '16 at 03:23
@deadrat Erm, definitely not Mr Deadrat! The word that isn't a relative pronoun in the OP's sentence. It's a subordinator. — Araucaria - Him, Jan 18 '16 at 09:29
@Rathony I'm not sure that's a good page to link to because it's a mishmash of relative that, pronoun that and subordinator that. The subordinator that does not get a good treatment on that page, in my opinion (see my answer here for comparison). — Araucaria - Him, Jan 18 '16 at 10:08
@Araucaria How can I possibly disagree with you? But isn't the question for ELL? — , Jan 18 '16 at 10:21
@Rathony I think that the behaviour of the subordinators is probably of interest to linguists if handled in an appropriate way. It would fit on ELL too no doubt :-) — Araucaria - Him, Jan 18 '16 at 10:30

score 2 · Answer 1 · edited Mar 07 '20 at 12:04

I'm sure your friends will likely call you on your birthday

In the sentence above, the phrase your friends will likely call you on your birthday is a Complement of the adjective sure. This type of clause is known as a content clause (as opposed to a relative clause, or a comparative clause).

Content clauses are often introduced by the subordinator that:

I know [that you ate my last chocolate biscuit].

We only use that with declarative content clauses, not interrogative ones or exclamative ones:

*I wonder that if she is going to the party. (ungrammatical)
*I saw that how big the elephant was! (ungrammatical)

When to use that in declarative content clauses

We always use that with a content clause when a content clause is the Subject of a sentence:

[That you were late again] will not impress the powers that be.
*[You were late again] will not impress the powers that be. (ungrammatical)

We also always use that if the content clause has been moved to a position before the Subject:

[That I need help] I freely admit.

The sentence above is a version of I freely admit that I need help, where the Complement of admit has been moved to before the Subject, I.

We rarely use that if the content clause is the Complement of a preposition:

I will see you after you've finished your meeting.
*I will see you after that you have finished your meeting. (ungrammatical)

[There are a handful of very unusual prepositions such as notwithstanding which allow that.]

In nearly all other cases where the content clause is the Complement of a verb, noun, or adjective the word that is optional. It can be omitted or included as you see fit:

I know that you ate my biscuits.
I know you ate my biscuits.
I'm happy you ate my biscuits
I am happy that you ate my biscuits.
The fact you ate my biscuits really gets my goat.
The fact that you ate my biscuits really gets my goat.

We are far more likely to omit that if it's the Complement of a simple high frequency verb, adjective or noun. We are also far less likely to omit that in formal writing:

The notion you ate my biscuit is laughable. (slightly awkward because of notion)
We therefore need to underline we are going to be there. (awkward because formal and because of the long as well as low frequency verb underline)

Conclusion

In the Original Poster's sentence the content clause is the complement of the simple and high frequency adjective sure. The context is also not formal. The Original Poster can therefore freely omit that. The sentence will be both grammatical and appropriate.

References

^{Most of this information is available in:} ^{A Student's Introduction to English Grammar Huddleston & Pullum, 2005.}

I'm a bit unsure about the distinction between exclamative and declarative. For instance: "I was told who is going to the party" and "I was told how big the elephant is." Are these exclamative? They can't take a that either. Is there perhaps a simpler rule, like don't mix a who or how with a that? — Jacinto, Jan 18 '16 at 11:06
@Jacinto That kind of rule might end up being a bit more complicated. Your sentences are actually types of fused relative constructions (relative clauses without antecedents). Probably a good rule of thumb is don't use that with interrogative if or with a wh-word, if the wh-word is at the front of a single clause. If the wh-clause is embedded in a larger clause, then you might be able to use that: "We know that [who did it] is not the main problem". Here you can use that because the following wh-clause is part of a larger declarative clause "[wh-clause] is not the problem". — Araucaria - Him, Jan 18 '16 at 12:49

'I'm sure your friends will likely call you on your birthday.' Is "that" required?

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