Clefting involves the division and repackaging of the information in one clause into two parts, creating an additional clause. Traditional grammar instruction does not explain clefting. Although clefting is common in English, it can be difficult for second-language learners to master.
These cleft formers function as the subject of the newly-created clause.
Jack saved Rose's life.
It was Jack who saved Rose's life.
The Capitan warned the president of the White Star Line about taking on too much speed.
It was the Capitan who warned the president of the White Star Line about taking on too much speed.
Rose wanted to run away with Jack.
What Rose wanted to do was to run away with Jack.
To run away with Jack is what Rose wanted to do.
There is / there are clefts
Over two thousand people were on the Titanic.
There were over two thousand people on the Titanic.