As mentioned earlier, prevent and deter can sometimes mean the same thing. Deter is often used when the other party has a choice. It generally implies threatening to take an action in response. The police can deter a bad person from breaking the law. (The police are threatening to put someone in jail / hurt them.) Nuclear deterrence is based on mutually assured destruction. (You are deterring a country from using a nuclear weapon.) Prevent can be used more generally -- the thing that is happening may not be a person or organization. Prevention implies preparation. The goalie's job is to prevent the ball from going in the goal. (You can't deter a ball.) Locking your doors can prevent crime. Using a spellchecker can prevent typing mistakes. Wearing a condom can prevent disease transmission.

"Deter" means to persuade/threaten someone from doing something. Prevent means to stop something/someone by physical or other means. Examples:1. In my classes I deter students from being rude to each other by asking them to stay behind for 5 minutes after the lesson. 2. Teachers can prevent students from fighting in the yard at lunch time by standing in between them.

Both are quite similar. Deter means to discourage someone from doing something, and prevent means to obstruct a person from doing something. Either one can be used in the same sentence. :)