We use it to refer back to something that was just mentioned, talked about, or written. It is a pronoun, and it replaces a noun used in the previous sentence. When you use it, there is no special nuance or emphasis:
- I went to Jack’s party last night. It was so much fun. It replaces “Jack’s party.”
- We are planning a trip to Asia. It will be about three weeks long. It replaces “a trip to Asia.”
- Have you ever seen Casablanca? It’s a great movie. It replaces “Casablanca.”
We also use this and that to refer back to something that was just mentioned, talked about, or written. This and that are also pronouns and have more of stronger nuance or emphasis. This and that have the nuance that what came before this and that is something special or a new or interesting. I feel that when using this and that we tend to add more information after this and that than we do after it. Compare these two sentences:
- I went to Jack’s party last night. It was so much fun.
- I went to Jack’s party last night. That was an amazing party. The food was great and everyone had a great time.
So after it we usually say “a little information”, but after this and that we tend to say “more information.”
- We are planning a trip to Asia. This will be the first time for both of us to visit China, Japan and Korea.
- Have you ever seen Casablanca? That is probably one of the most classic films of the last century.