I know what ergative verb is -
Consider the following sentences -
I opened the door.
The door was opened (by me).
The door opened.
The verb open is a transitive verb in sentence #1, and sentence #1 is in active voice. The doer here is I, and what is affected by my action is door
Sentence #2 is in passive voice.
Sentence #3 is in middle voice. The verb open is used as intransitive way. And here the doer of the action (verb) is not important and is not mentioned. What is affected is the subject - door. So here the verb - open - is used in ergative form.
Consider sentence #1 and sentence #3. The object of the transitive verb in sentence #1 is the subject of the intransitive verb in sentence #3.
But all intransitive verbs can't be used in ergative form, nor all ergative verb can take everything as subject. For example -
He fired a gun.
The gun fired.
He fired a bullet.
A bullet fired (we can't use "bullet" as the subject of this ergative verb) - Incorrect sentence
MY QUESTION -
All ergative verbs are transitive verb in nature. But when they are used in ergative form they acts as intransitive. Am I right?
How to decide which verb can be used in ergative form and which verb can not? Is there any technique - logical or grammatical or anything else?
How to decide which subjects are appropriate for a particular ergative verb, and which are not?