The sun melted the butter.
The butter melted.
Here, the subject was the object of the original sentence. The butter didn't melt itself- it required the heat of the sun. This is an ergative verb use, where the subject of the intransitive form of the verb would be the object of the transitive form of the verb.
Auxiliary Verb; Ditransitive Verb; Dynamic Verb; Finite Verb; Inchoative Verb; Intransitive Verb; Irregular Verb; Middle Verb; Modal Verb; Performative Verb; Regular Verb; Stative Verb; Transitive Verb; Verbs; Verb Group; Verb Phrase; Main Verb; Parts of Speech
Verbs and Tenses