Sure-Surely | Commonly Confused Words

Sure

/ʃʊə/

Being certain or confident about something without a doubt.

Old Mrs Smith did not invite you, I am sure."But if Lyon calls you, please tell him." "Sure, sure.Clients like the two of you I sure need!"

/ˈʃɔːli/

Certainly or without doubt

'Surely that must content you!Surely the idea is too fantastic."Surely there is enough evidence against him.'

Sure can function as both an adjective and an adverb, while surely is solely an adverb.
Use sure when you want to express certainty or agreement.
Use surely to reinforce a statement or as a form of emphasis, often to persuade or reassure someone.