Unless

When do I use Unless?

[Francois]

When you deal with special cases.

FRC

[bmo]

Originally Posted by Francois

When you deal with special cases.

FRC

Francois is right.

Conjunction:
Unless=except on the condition that; except under the circumstances that.

I won't marry you unless you buy my parents a 4-story house in downtown Taipei.

Preposition: (from www.wordsmyth.net)
=except possibly.
Example: There is no cure for his illness, unless an operation.