Not all of the member countries of the European Union will be strong in foreign policy. Why? For all members of an alliance to be strong in foreign policy the alliance must respond aggressively to problems, to respond aggressively to problems all members of an alliance must perceive the problems as grave, and for all of the European Union countries to to perceive a problem as grave they must all agree the problem threatens their alliance’s economy.

The political theorist concludes that not all of the member countries of the European Union will be strong in foreign policy but doesn’t explain why.

Shown in the conditional diagram above, all member countries of the European Union being strong in foreign policy is a sufficient condition with multiple necessary conditions following it. The conclusion is just a negation of that sufficient condition (the condition “strong”). How to arrive at the conclusion from the premises? We need an answer choice that negates any of the necessary conditions of “strong” (so the correct answer could negate “respond aggressively,” “all perceive as grave,” or “all agree.”) Negating one of the necessary conditions of “strong” would trigger the contrapositive, also negating “strong.”