How will I know? と How would I know の違いは何です?

What is the difference between how will I know and how would I know?

Use how will I know in factual situations.
For example,
How will you know Valentine's day is around the corner?
All the store shelves in Japan will be full of chocolate.

Here is another one.
How will you know you what the weather is going to be like the next day?
Check the weather forecast the night before.


Use how would I know when you are asked something unexpected or when it is something you have no idea about.

For example,
A: What currency do people use in Madagascar?
B: How would I know? I have never been there.

A: How does it feel like to be drunk?
B: How would I know? I am a teetotaler.

I searched the Net for songs titled How will I know and How would I know...
Interestingly enough I found two songs. One of them was sung by Whitney Houston. It was one of her big hits and the other was sung by Melissa Etheridge.

Check 'em out...
Here is Melissa Etheridge's song...
http://www.youtube.com/watch?v=rfMcqpCL3-o

and here is Whitney's old hit.
http://www.youtube.com/watch?v=aiJ_2zQYUFg