Law School Discussion

In "Necessary" question type, how can I negate answer choices that contain Only

i.e) Only when behaviors become typical among an animal population can we conclude that genetic alteration has occurred in that variety of species.

i.e) Only when behaviors become typical among an animal population can we conclude that genetic alteration has occurred in that variety of species.

would this work?

When SOME behaviors become typical among an animal population we can't conclude that genetic alteration has occured in that variety of species.

NOT Only when behaviors become typical among an animal population can we conclude that genetic alteration has occurred in that variety of species.

That's the way I usually do it- not sure if it's right either though...??  I just usually try and stick "not" anywhere i can to negate.

i.e) Only when behaviors become typical among an animal population can we conclude that genetic alteration has occurred in that variety of species.

Hopefully this doesn't get too far into formal logic.

So first, translate it: If genetic alteration has occurred in a variety of species, then behaviors have become typical among the population.

g --> b

Negate it: ~(g --> b)

g --> b is equivalent to ~g v b, so we have:

~(~g v b)

Finally, DeMorgan's: g & ~b

So yes, the negation of a conditional is always a conjunction of the antecedent and the negation of the consequent. Which makes sense, because all a conditional is telling you is that it can never be the case that both the antecedent is true and the consequent is false. If you have the negation of that, then it means the antecedent is true, but the consequent is still false.


Oh, so I guess to tie it all back with the original sentence, the negation would be "Genetic alteration has occured in a variety of species, but behaviors have not become typical among the population."

i.e) Only when behaviors become typical among an animal population can we conclude that genetic alteration has occurred in that variety of species.

I would negate it as "We can conclude that genetic alteration has occurred even when bahaviors have not yet become typical among the animal population."

I get there just by examining the meaning of the statement, and then trying to state the logical opposite.

yeah i like to examine the meaning also but sometimes i go back and forth from doing that and inserting a "not" when i can.

so was my example of doing it wrong?

i.e) Only when behaviors become typical among an animal population can we conclude that genetic alteration has occurred in that variety of species.

I would negate it as "We can conclude that genetic alteration has occurred even when bahaviors have not yet become typical among the animal population."

I get there just by examining the meaning of the statement, and then trying to state the logical opposite.

This is how I learned to negate from TM.


So yes, the negation of a conditional is always a conjunction of the antecedent and the negation of the consequent. Which makes sense, because all a conditional is telling you is that it can never be the case that both the antecedent is true and the consequent is false. If you have the negation of that, then it means the antecedent is true, but the consequent is still false.

Why didn't you just say this up front?  It's all so simple now!!!   :D

Good, I'm glad I could help!!!!! :D