That vs What

[SourChipmunk]

THAT is a pig.

WHAT is a pig?

THAT is WHAT a pig is.

 

[mctiny]

Basically 'What" is for questions, and that is to state soething/point out what something is, I.e. "that is a pig" as above.

I'll check in my grammar books and see if it comes up with anything more...

 

[Johnny Girth]

Tell him that you use "what" when you don't know what the thing is you're talking about and "that" when you do.

So "that" place that you went to - because you know the place.

"What" am I going to get for Christmas? / I don't know "what" I'm going to get for Christmas - because you don't know that you're getting.