happen -> случаться
Образование времен: Субъект подвергается (Пассив, или иначе страдательный залог)
  Past - ПрошлоеPresent - НастоящееFuture - Будущее
Факт - Simple
I/he/she/itwe/you/they
was happenedwere happened
---
was not happenedwere not happened
wasn't happenedweren't happened
Ihe/she/itwe/you/they
am happenedis happenedare happened
---
am not happenedis not happenedare not happened
 isn't happenedare'nt happened
I/he/she/it/we/you/they
will be happened
---
will not be happened
won't be happened
Процесс - Continuous
I/he/she/itwe/you/they
was being happenedwere being happened
---
was not being happenedwere not being happened
wasn't being happenedweren't being happened
Ihe/she/itwe/you/they
am being happenedis being happenedare being happened
---
am not being happenedis not being happenedare not being happened
 isn't being happenedare'nt being happened
Завершенность - Perfect
I/he/she/it/we/you/they
had been happened
---
had not been happened
hadn't been happened
I/we/you/theyhe/she/it
have happenedhas happened
---
have not happenedhas not happened
haven't happenedhasn't happened
I/he/she/it/we/you/they
will have been happened
---
will not have been happened
won't have been happened
Вместо отсутствующих форм Perfect Continuous употребляются формы Perfect
happen -> случаться