effect vs happen

effect is a noun but happen is not a noun.

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

effect (noun)	happen (noun)
an outward appearance
(of a law) having legal validity
an impression (especially one that is artificial or contrived)
the central meaning or theme of a speech or literary work
a phenomenon that follows and is caused by some previous phenomenon
a symptom caused by an illness or a drug

effect (verb)	happen (verb)
produce	come to pass
act so as to bring into existence	come into being; become reality
	happen, occur, or be the case in the course of events or by chance
	come upon, as if by accident; meet with
	chance to be or do something, without intention or causation