sufficient (S) = if S happens then X must happen

necessary (N) = if N does not happen then X cannot happen

Interestingly enough, S not happening doesn't mean X won't happen and N happening does not mean X will happen. Which I think would have made total sense to me if you hadn't spent a bunch of exercises teaching me how to use the contrapositives of everything with no care as to whether it's necessary or sufficient.

Number 4 feels wrong logically because if you know how to cast Herbivicus Charm, then you can mix plant material into garden soil and if you do that then the number of beneficial soil bacteria will increase. That connection feels logical, yet lawgic claims there's no connection. What am I missing?

Why does "all cats are mammals" not get translated in lawgic to C^M since it is stating that all Cats are members of Mammals and not "If cat, therefore mammals"?