Passive auxiliary verbs and verbs not used in passive

Passive Auxiliary verbs

Passive voice constructions can also be used with “modal auxiliary verbs” (can, might, etc.), such as in the following examples:

Active Voice, Passive Voice

I can stop, I can be stopped
I might stop, I might be stopped

Notice that the passive voice constructions always appear after the modal auxiliary verbs.

Verbs that cannot be used in passive

An intransitive verb expresses that someone or something takes action to do something—by itself.  The verb does not accept an object (noun) as its complement. A passive structure cannotbe formed.

Eg: The audience laughed.

The kids smiled.