Passive voice non-existent in the active
III. Passive, to be concerned.
This occurs in some senses which are non-existent or obsolete in the active; in other senses it is much more used than the active.
https://www.oed.com/oed2/00046215
Are there passives without a corresponding active?
It's the normal grammatical definition of the passive voice, in which the object of a transitive verb is made into the subject.
For example, if a sentence in the active is:
I gave my roommate a ride,
the passive would be
My roommate was given a ride by me.
To see what the OED is talking about in that some of the meanings of concern are only used in the passive, one of the meanings for which the active of concern is not used is
- a. To be in a relation of practical connexion with; to have to do with; to have a part or share in; to be engaged in, with:
1875 Jowett Plato Music is concerned with harmony and rhythm.
This sentence sounds fine, but if you put this in the active you get:
Harmony and rhythm concern music,
which sounds really wrong.