Here. The article is about word-pairs that are often confused. Like “further/farther”, “less/fewer”. But the first pair caught my attention:
“Sure” and “certain”
Both are used to express no doubt about something, but they are used differently depending on how one concludes that there is no doubt.
“Sure” is used to express one’s belief of no doubt through intuition or feeling: “I am sure she loves me” or “I am sure we will get the apartment we want” or “I’m sure my life is going to get better.”
“Certain” is used when one’s conclusion of no doubt is based on facts, evidence, or definite grounds of some kind: “After reading the police report, I am certain the man is innocent” or “My research makes me certain my theory is correct” or “After studying the minutes, I am certain the city council made the right decision.”