happen vs occur

happen and occur both are verbs.

Word	Noun	Adjective	Verb	Adverb
happen	No	No	Yes	No
occur	No	No	Yes	No

As verbs, happen and occur are synonyms defined as:

Other synonyms of happen include come about, fall out, go on, hap, pass, pass off, take place.

As verbs, occur is a hypernym of happen; that is, occur is a word with a broader meaning than happen:

Other hypernyms of happen include come about, fall out, go on, hap, happen, pass, pass off, take place.

As verbs, occur is a hypernym of happen; that is, occur is a word with a broader meaning than happen:

Other hypernyms of happen include come about, fall out, go on, hap, happen, pass, pass off, take place.

happen (verb)	occur (verb)
come to pass	come to pass
come into being; become reality	come to one's mind; suggest itself
happen, occur, or be the case in the course of events or by chance	to be found to exist
come upon, as if by accident; meet with
chance to be or do something, without intention or causation