A that-clause is a subordinate clause introduced by the word that. It acts as the object of the main verb — it tells us what someone thinks, says, knows, or feels.
The whole clause that she is right is what I think. It works like a single noun: you could replace it with something and the sentence would still hold — I think something.
The pattern
The basic structure is straightforward:
Subject + verb + (that) + clause
The clause after that has its own subject and verb. It is a complete thought attached to the main verb.
Verbs followed by that-clauses
Not every verb takes a that-clause, but many common ones do. They fall into three natural groups.
Thinking and knowing
think, believe, know, understand, imagine, suppose, expect, doubt, feel, realize
Saying and reporting
say, tell, explain, mention, report, announce, claim, suggest, admit
Feelings
hope, wish, fear, regret, worry
Dropping "that"
In everyday English, the word that is often left out. Both versions are correct and mean exactly the same thing.
This happens constantly in speech and informal writing. In more formal texts — reports, academic papers, news articles — that tends to stay.
There is one practical reason to keep that: clarity. When the sentence has a long subject or could be misread without it, that prevents confusion.
Removing that here (The report confirmed the data was accurate) is fine, but in longer, more complex sentences the reader benefits from the signpost.
Say vs. tell
Both verbs introduce that-clauses, but their grammar is different.
Say does not need a person after it:
Tell always needs a person — it answers told whom:
| VERB | PATTERN | EXAMPLE |
|---|---|---|
| say | say (that) + clause | She said she would call later. |
| tell | tell + person + (that) + clause | She told him she would call later. |
This difference applies in every tense: says / said / will say vs. tells / told / will tell someone.
Wh-clauses as objects
The same group of thinking and saying verbs can also take a clause introduced by a wh-word: what, where, when, why, how, who, which.
These clauses function exactly like that-clauses — they are the object of the main verb.
Word order inside wh-clauses
This is where most mistakes happen. Inside the wh-clause, the word order is statement order, not question order. The subject comes before the verb.
Compare this with the direct question:
The moment the wh-word introduces a clause inside a larger sentence, the question inversion disappears.
If / whether clauses
When the answer is yes or no rather than a specific piece of information, English uses if or whether to introduce the clause.
The same statement-order rule applies: the subject comes before the verb, with no question inversion.
If and whether are interchangeable in most cases. Whether sounds slightly more formal and is preferred in writing when two options are spelled out: whether to stay or leave.
Common mistakes
Question word order inside clauses
Tell without a person
Say with a person
Missing statement order after if/whether
Mixing up that-clauses and questions