hap·pen 
/ˈhæpən/ verb
hap·pens; hap·pened; hap·pen·ing /ˈhæpən/ verb [no obj] 1 : to take place especially without being planned : occur
▪ Mistakes/Accidents will happen. ▪ Something like that was bound to happen sooner or later. ▪ You never know what's going to happen when they get together. ▪ What happened at school today? ▪ “What's happening?” “They're installing new equipment.” 2 not used in progressive tenses a : to do or be something by chance — followed by to + verb ▪ The children happened to be asleep when we called. ▪ I happened to overhear their conversation. ▪ I happen to know his brother. ▪ Do you happen to know the way to the station?
b — used with it to describe something that occurs by chance ▪ It (so) happened that the children were asleep when we called. ▪ It happened to rain that day. ▪ As it happened, it rained that day. ▪ It (just so) happens that I know his brother.
c — used to make an angry or forceful statement — followed by to + verb ▪ The woman you've been looking at happens to be my wife! ▪ I happen to think that the movie was actually very good.
▪ Mistakes/Accidents will happen. ▪ Something like that was bound to happen sooner or later. ▪ You never know what's going to happen when they get together. ▪ What happened at school today? ▪ “What's happening?” “They're installing new equipment.”
b — used with it to describe something that occurs by chance ▪ It (so) happened that the children were asleep when we called. ▪ It happened to rain that day. ▪ As it happened, it rained that day. ▪ It (just so) happens that I know his brother.
c — used to make an angry or forceful statement — followed by to + verb ▪ The woman you've been looking at happens to be my wife! ▪ I happen to think that the movie was actually very good.
happen along or happen by
[phrasal verb] US, literary + old-fashioned : to come to or by a place by chance
▪ He was about to leave when his old girlfriend happened by.
▪ He was about to leave when his old girlfriend happened by.
happen into [phrasal verb]
happen into (a place) US : to enter (a place) by chance
▪ She happened into the room just as the music started.
▪ She happened into the room just as the music started.
happen on/upon [phrasal verb]
happen on/upon (someone or something) literary + old-fashioned : to find or meet (someone or something) by chance
▪ She happened on a little cottage in the woods. ▪ I happened upon them at the grocery store.
▪ She happened on a little cottage in the woods. ▪ I happened upon them at the grocery store.
happen to [phrasal verb]
happen to (someone or something) : to affect or involve (someone or something) as the result of an event or action
▪ An odd thing happened to me on my way to the office last week. ▪ I wonder what/whatever happened to that guy. [=I wonder where that guy has gone and what he has been doing] ; especially : to affect (someone or something) in a bad or harmful way
▪ I promise nothing will happen to you. ▪ What happened to the car? There's a big scratch on the fender.
▪ An odd thing happened to me on my way to the office last week. ▪ I wonder what/whatever happened to that guy. [=I wonder where that guy has gone and what he has been doing] ; especially : to affect (someone or something) in a bad or harmful way
▪ I promise nothing will happen to you. ▪ What happened to the car? There's a big scratch on the fender.
