We form the transitive verb from the intransitive verb just by adding an object. No real mystery there. Ergative verbs have an extra property, however. Take the sentence: (1) The meeting opened at 12:00.. Logically, the meeting actually did nothing: to be precise we could say (2) Someone opened the meeting. If we want to focus on the meeting we could use the passive: (3)The meeting was opened at 12:00.. But open is ergative, allowing us to recast the object of the verb used transitively ( the meeting in sentence (2)) as the subject of the verb used intransitively (Which is (1))..