Sure vs certain

"Sure" and "certain" are both used to express lack of doubt about something. But they are used differently, depending on how one reached the conclusion that there is "no doubt."

"Sure" is used to express ones belief of "lack of doubt" through intuition or feeling: for example, "I am sure she loves me" or "I am sure I did well on the exam" or "I am not sure I turned off the iron."

 

"Certain," on the other hand, is used when one reaches the conclusion of "absence of doubt" based on facts, evidence, or definite grounds of some kind, rather than feeling: for example, "After looking at the report, I am certain the company did the right thing" or "The police are certain that the evidence confirms his guilt."

Dr. William B. Bradshaw
Author/educator/grammar guru