refer vs hark back

refer and hark back both are verbs.

Word	Noun	Adjective	Verb	Adverb
refer	No	No	Yes	No
hark back	No	No	Yes	No

As verbs, hark back is a hyponym of refer; that is, hark back is a word with a more specific, narrower meaning than refer:

refer (verb)	hark back (verb)
think of, regard, or classify under a subsuming principle or with a general group or in relation to another	go back to something earlier
have as a meaning
make reference to
use a name to designate
seek information from
send or direct for treatment, information, or a decision
be relevant to