Is prevention of action a requirement for someone to be 'deterred'?

Solution 1:

To prevent and deter are different, you prevent a person leaving by locking the door and keeping the only key, you deter from leaving them by convinvincing them not to leave for whatever reason. You do not prevent somebody completing and action by convincing them not to because if they are convinced not to, then they had choice and were not prevented.

To be prevented is to be stopped by an outside force and to be deterred is ultimately the person's decision based on the deterrent factors.

When they change their mind and follow through with the action they are no longer deterred.

To answer the question look at the word undeterred, if a person was undeterred, they complete the action without hesitation regardless of what deterrents are in the way. If they were hesitant but continued, they may have been deterred in some way although have overcome that.

At the point the date in the example occurred he was no longer deterred although he had been deterred at the point he was scared of being punched.

Solution 2:

This is a very good question and the OED does not provide clarity.

The word comes from the Latin deterrere - to frighten. But that doesn't get us far.

OED sense 1a says:

trans. To discourage and turn aside or restrain by fear; to frighten from anything; to restrain or keep back from acting or proceeding by any consideration of danger or trouble.

1854 H. H. Milman Hist. Lat. Christianity I. iii. vii. 461
Maurice..had been deterred by the alarming prophecy of a monk. 1877
J. D. Chambers Divine Worship Eng. 308 To deter instead of to invite communicants.

In practice I suspect "deter" does get used both ways.

People definitely say things like "he was undeterred" - meaning, presumably, he was not prevented.

But I feel sure that it is also used, in the following sense too "health warnings on cigarette packets are a deterrence, but some still smoke".

Unlike "prevent", "deter" is uncertain. If I say "I will prevent it from happening" you know the eventual outcome. It will not happen. But if you say "I will deter him from coming" - you don't at that moment know if it will work. He may still come. But you still use the word "deter". So in that sense "deter" is only an action designed to prevent. However if I say "He was deterred from going", at that point I know the outcome - so the meaning is that he didn't go. So the meaning is dependent on whether you know the outcome.