Two superficially different sentences are
shown in these examples:
Charlie broke the window.
The window was broken by Charlie.
In traditional grammar, the first is called an
active sentence, focusing on what Charlie did,
and the second is a passive sentence, focusing
on The window and what happened to it. The
distinction between them is a difference in
their surface structure, that is, the different
syntactic forms they have as individual English
sentences. However, this superficial difference
in form disguises the fact that the two
sentences are very closely related, even
identical, at some less superficial level.