When must one use "either" instead of "any"?
I came across this sentece:
In either of these cases, your strategy is the same.
I should have written any. Now, I'm confused about the usage of either.

Question

When must one use "either" instead of "any"?
I came across this sentece: 
In either of these cases, your strategy is the same. 
I should have written any. Now, I'm confused about the usage of either.

Answer

'Either' only applies to two choices. 'Any' applies to any number of choices.