Drill 119: Find the Mistake, p683 - unless mistake?

[BarbC178]

Hi,

Can you explain to me why number 23 is not diagrammed like this:


G or F is at the party unless H and K are.

-G or -F --> H AND K
(-H or -K --> G AND F)

In the book, both necc and suff terms have an "OR."

I use the "unless = neccessary, negate sufficent" method.

Thanks!

Barb

[Laura Damone]

That's such a tricky one! When you negate "G or F" it becomes "-G and -F." And if you think about it, that makes sense: in order for it not to be true that G or F is present, it must be true that both G and F are absent. An easy way to remember this moving forward: the negation of "either/or" is "neither/nor".

Hope this helps!