When we say what people and things do, we use active verb forms. When we say what happens to people and things – what is done to them – we often use passive verb forms.

• They built this house in 1960. (active)
• This house was built in 1960. (passive)
• This book will change your life. (active)
• Your life will be changed by this book. (passive)

The object of an active verb corresponds to the subject of a passive verb.

• They built this house (object) in 1960.
• This house (subject) was built in 1960.

In most cases, the subject of an active verb is not mentioned in the corresponding passive sentence. If it does have to be mentioned, this usually happens in an expression with by.

• This house was built in 1960 by Sir John Elton.