For certain and Without doubt

For certain adverb - Definitely or positively (`sure' is sometimes used informally for `surely').

Without doubt and for certain are semantically related. In some cases you can use "Without doubt" instead the phrase "For certain" as an adverb or an adjective.

For certain and without doubt are semantically related. Sometimes you can use "For certain" instead the phrase "Without doubt" as an adjective or an adverb.