Political theorist: For all of its members to be strong in foreign policy, an alliance of countries must respond aggressively to problems.
Conclusion (Thus)
Not all members of the EU will be strong in foreign policy. rephrase: At least one member of the EU will not be strong in foreign policy.
Evidence
All members → Respond strong in FP aggressively
Respond → all see as aggressively grave
all see as → all agree grave threat to $
Evaluate
The first three sentences give us three conditionals. Must = right side (Required = Right) Only if = right side Unless = rephrase into 'X requires Y' form, or do an "If-not" (put the negated version of one of the ideas on the left side of an arrow, the regular version of the other idea on the right side of the arrow)
The easiest way to mentally or conditionally chain them is to take advantage of the "X requires Y" way of reading "X → Y".
For all members to have strong foreign policy it requires responding aggressively to problems which requires perceiving the problems as grave which requires all agreeing it threatens their economy
So the evidence gives us a conditional chain. Str FP → Rsp Agg → Per Grave → Agree Threat And the conclusion is stating factually, Str FP.
It looks like we need to use the contrapositive of this chain. ~Agree → ~Per Grave → ~Resp Agg → ~Str FP
Goal
To prove that Str FP, we just need to know that - they won't all agree it threatens economy - they won't all perceive as grave or - they won't respond aggressively