surely vs for certain

surely and for certain both are adverbs.

Word	Noun	Adjective	Verb	Adverb
surely	No	No	No	Yes
for certain	No	No	No	Yes

As adverbs, surely and for certain are synonyms defined as:

surely and for certain: definitely or positively (`sure' is sometimes used informally for `surely')

Other synonyms of surely include certainly, for sure, sure, sure as shooting, sure enough.

surely (adverb)	for certain (adverb)
definitely or positively (`sure' is sometimes used informally for `surely')	definitely or positively (`sure' is sometimes used informally for `surely')