simply vs but

simply and but both are adverbs.

Word	Noun	Adjective	Verb	Adverb
simply	No	No	No	Yes
but	No	No	No	Yes

As adverbs, simply and but are synonyms defined as:

Other synonyms of simply include just, merely, only.

simply (adverb)	but (adverb)
and nothing more	and nothing more
in a simple manner; without extravagance or embellishment
absolutely; altogether; really
(used for emphasis) absolutely