What is the difference between 防止 and 予防? My dictionary defines both and as "prevention", with having the additional definitions of "precaution" and "protection against". I sort of understand the latter definitions for as acting to stop something which is happening from getting worse, which explains its use in medicine, but I've also seen used in the "prevention" sense similar to . For example, from the Tanaka Corpus: > **** > The prevention of forest fires is everyone's responsibility. > > **** > This is Fire Prevention Week. > > **** > We must take measures to prevent traffic accidents. > > **** > Defensive driving can help you avoid accidents. > > **** > It is essential to prevent salmonella contamination in hen egg production. > > **** > Prevention is much preferable to cure. [sic] In what situations is it preferable to use over ? What are the nuances that govern the choice of one word over the other?

The key to understanding the difference is in the characters, the of can be seen in the phrase also, meaning "in advance" or "beforehand". While the of can be seen in the phrase , meaning "to stop something". In other words, doesn't mean to stop something, it means to do something in advance to _try_ to prevent it as you aware that it might happen, whereas just means to stop something from happening (prevent it) and doesn't include the "in advance" part.

So, to take your first two examples:

means to stop (prevent) forest fires, whereas implies doing something in advance to try to prevent fires from happening as you are aware that they might happen.