What’s That About?

There are four words that are easily confused by students: then, than, that, what. It’s understandable how these words are confused. By changing one letter, the word transforms into another one! Then gets confused with than, than with that, and especially that with what. So I think it would be useful to review when we use these words.

Use then for sequencing:

First, read the story, then answer the questions. 

What happened then?

Use than to make comparisons.

She's taller than me.

I'd rather have these than those.

Use that to replace a specific object which is far in place or time:

I like the picture over there. I like that.

Remember when we went to China. I remember that.

But what for an unknown object:

This is what I'm talking about.
What are you talking about?

I am what I am. 

You can use that (not what) instead of which or who in relative phrases to attach a phrase to a noun:

This is the job which I want to have 

This is the job that I want to have.

This is the person who I want for the job.

This is the person that I want for the job.

Use that can be used optionally between abstract verbs and a subject:

I think (that) it is a good idea!

Or optionally between adjectives and a subject:
I'm glad (that) you got the promotion!
You can also use that optionally in reported speech:

I would like to go. She told me (that) you would like to go.

But use what in some reported questions:

What are you doing? She asked me what I was doing.

And use what in some indirect questions:

I don't know what you're doing.

I hope that that's all clear now!