Match the Reasoning Conditional Logic

[NoraS176]

I had a questions about some conditional logic phrasing that I can't wrap my head around. This type of logic appeared in as an answer choice in a match the reasoning question about archaeology or ancient civilization, something like that:

taking the nonexistence of something as evidence that a necessary precondition for that thing also did not exist

Abstract:
y is a necessary precondition for x.......x requires y....... x therefore y
Answer says: ~ x therefore ~ y
Illegal negation

Alternate Example:
Spanish 1 is a necessary precondition for Spanish 2..... Span2 requires Span1... Span 2 therefore Span 1.
Saying "Spanish 2 does not exist on Shelia's transcript, so I'm going to treat that as evidence that Spanish 1 also does not appear on her transcript" doesn't make sense at all. Invalid argument due to illegal negation.

I think the term "necessary precondition" is tripping me up. Am I thinking about the conditional logic correct?

[ohthatpatrick]

It sounds like you're totally nailing it. Those are perfect examples.

A necessary precondition is just a fancy way of saying "a necessary condition".

I think the term 'precondition' is just conveying an additional temporal dimension of "it's not only necessary, it would have occurred earlier".

I kinda think of all Necessary conditions as earlier, as preconditions, but you could probably think of a simultaneous one.

"In order for Nora to date someone, they must have a cool hairstyle."

That requirement doesn't necessarily need to predate you dating someone (unfortunate pun there). It would be okay if their hairstyle sucked prior to dating you.