These words mean filled with wonder or incredulity because of a confrontation with something unexpected. To be surprised is to meet with something that momentarily, at least, sets one back and then may or may not afford pleasure: surprised to receive a letter from a friend she had not heard from in years; surprised at the drunken behaviour of a business associate whom he had always looked up to. The word can suggest also a certain amount of moral condemnation, as when a person says "I’m surprised at you!"

Astonished is a stronger word, indicating that a person has had more than an ordinary reaction to the unexpected: astonished to see how his home town had changed in the past 25 years.

Amazed suggests great wonder or bewilderment in the face of something that seems impossible or highly improbable: a teacher amazed to find that a lazy student had gained a mark of 100 in an important test. Astounded and the informal flabbergasted express extreme difficulty of belief. A woman may be astounded to learn that her dearest friend has been spreading malicious gossip about her. Describing her reaction to another friend, she might say, "I was flabbergasted !"

Stunned indicates shock and even speechlessness: a congregation stunned to hear that their minister has just confessed to a serious crime.