Cleft sentences

A declarative sentence, such as
David studied English at Oxford can be reformulated as:
It was David who studied English at Oxford

This is called a CLEFT SENTENCE because the original sentence has been divided (or "cleft") into two clauses:
It was David and who studied English at Oxford.

Cleft sentences focus on one constituent of the original sentence, placing it after it was (or it is).
Here we have focussed on the Subject David, but we could also focus on the Direct Object English:

It was English that David studied at Oxford

or on the Adjunct at Oxford

It was at Oxford that David studied English

Cleft constructions, then, exhibit the pattern:
It + be + focus + clause

We can also use preparatory it in cleft sentences and join the words that we want to focus on to the relative clause with that, who or when.

In the example which follows, note how this construction enables us to focus on different aspects of the information, which may be important at the time:

My brother bought his new car from our next-door neighbour last Saturday.

It was my brother who bought his new car from our neighbour last Saturday.
It was last Saturday when my brother bought his new car from our neighbour.
It was a new car that my brother bought from our neighbour last Saturday.
It was our next-door neighbour that my brother bought his new car from last Saturday.