certainly vs surely

certainly and surely both are adverbs.

Word	Noun	Adjective	Verb	Adverb
certainly	No	No	No	Yes
surely	No	No	No	Yes

As adverbs, certainly and surely are synonyms defined as:

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

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

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