What or That?

What or That?

Are you sometimes unsure about using the words “what” and “that”? Do you sometimes make mistakes when deciding which word to use in sentences like “I know what/that…” or “It’s not clear what/that…”? Read this article to understand the difference and practice using them correctly.

In grammar, “what” and “that” have different jobs in a sentence.

That” is often used as a word that shows a connection between two parts of a sentence (1). It can also be used to give more information about a noun or pronoun (2). For example:

I know that he is busy. (1) (I know + he is busy – “that” connects the two sentences into one.)

I have a dog that loves to play fetch. (2) (If you use “that” like this, you provide more information about the dog.)

If “that” connects two sentences into one, you can omit “that”. For example, I know he is busy.

Unlike “that”, “what” introduces a subordinate clause that functions as the object of the main clause. For example:

I know what you did. (I – subject, know – verb, what you did – object)

Find the object in the sentences: 1. I see a ball. 2. I hear a song. 3. I know what I want.

In the first sentence, the object is “a ball”, in the second – “a song”, and in the third – “what I want.” The object of the last sentence is more complex because it consists of a clause – a subject (I) and a verb (want), but it’s still an object, and it has to be introduced by “what” – never “that.”

But you can say “I know that I want a new ball.” This sentence is very similar to “I know that he is busy” because in both, “that” connects two “independent” parts of the sentence into one, so it’s also grammatical to say “I know I want a new ball.”

In summary, “that” is used to give more information about the noun – as a relative pronoun (e.g. I have a cat that likes to sleep) and to connect two sentences – as a conjunction (e.g. I see that we need more practice). “What” can function as a relative pronoun – to introduce the object of a sentence (e.g. I do what I want), and of course it can function as a question word, which “that” can’t (e.g. What is your name?).


Click the link here and complete the sentences with either “what” or “that.”

Do you still have questions? Feel free to ask them in the comments below. 👇

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