Differences between “razón de,” “razón por la que,” and “razón para”

Question

I think I've heard three ways of translating "the reason [something happened]" or "the reason [for something]":

1. la razón para
2. la razón de
3. la razón por la que

What is the difference between these three constructions, and when would you use each?

Answer 1

I'd say the differences are very subtle, and in most cases you could use any of the three options without much difference. But anyway:

• "La razón para" generally would be used as "the reason for", as in "the reason to do something we have done in the past or are planning to do in the future".

  La razón para ilegalizar las drogas es que son malas para la salud.

• "La razón de" can be used in the same context as case no. 1, but also to explain the reason why some event happened.

  La razón de que el edificio se cayera es que estaba mal construído.

• "La razón por la que" can be used in the same context as cases 1 and 2, but is generally less used because it is longer. If you are using it like in case 1, the syntax is a bit different. You have to explain who's the one discussing the reason.

  La razón por la que el gobierno quiere ilegalizar las drogas es que son malas para la salud.