Thank you! This helped.

I agree. It appears it's a negation of both sufficient and necessary in the diagram. If you negate PFS- then necessary remains irrational. "Not irrational" would seem to be the better choice for the contrapositive.

Thank you. I intended "Right?" to be rhetorical. Tone can be hard to discern on message boards. I should have included the mapped-out version of the argument to indicate my intent to help. Perhaps our comments will work in tandem? :)

If a thing is a lemon drop, that thing is a flower. White-out is a lemon drop. Therefore, white-out is a flower.

Right?

I find the concept of the argument easier to grasp when remembered as the formula (A-B, xA then xB). Using ridiculous/not-at-all linked sets helps me practice the argument flow (in formula form) while reiterating, “The argument is valid because of its form, not content.”