#22 - Dinosaur expert: Some paleontologists have claimed that birds are descendants

[Dania_ha]

I am trying to understand why C is an incorrect answer choice. Isn't C a defender assumption that helps protect potential objections to the conclusion? In that case, wouldn't C also be a necessary assumption?

[Ryan Twomey]

Hey Daniaha,

C is a defender assumption. I think C could be a correct answer potentially if D were not present. C is just slightly less necessary than D when applying the negation test.

When we apply the negation test to D it completely wrecks the argument, whereas when we apply the negation test to C it only substantially weakens the argument.

When you negate D, the answer choice states:
"known fossils do not indicate the relative dates of origin of birds and dromesaurs."

This means they have no idea when these two species first arrived to the planet, completely wrecking their argument.

When C is negated, the answer choice states:

"knowledge of the earliest bird fossils and dromeosaur fossils is incomplete."

This certainly attacks our argument, but as long as we have a good understanding of their earliest finding, our conclusion is still relatively sound in comparison to answer choice D.

To summarize, answer choice D is just more necessary to the argument than answer choice C is. This is a case of having one good answer choice and one great answer choice.

I hope this helps, and I wish you all of the luck in your studies.

Best,
Ryan

[Dania_ha]

Hey Daniaha,

C is a defender assumption. I think C could be a correct answer potentially if D were not present. C is just slightly less necessary than D when applying the negation test.

When we apply the negation test to D it completely wrecks the argument, whereas when we apply the negation test to C it only substantially weakens the argument.

When you negate D, the answer choice states:
"known fossils do not indicate the relative dates of origin of birds and dromesaurs."

This means they have no idea when these two species first arrived to the planet, completely wrecking their argument.

When C is negated, the answer choice states:

"knowledge of the earliest bird fossils and dromeosaur fossils is incomplete."

This certainly attacks our argument, but as long as we have a good understanding of their earliest finding, our conclusion is still relatively sound in comparison to answer choice D.

To summarize, answer choice D is just more necessary to the argument than answer choice C is. This is a case of having one good answer choice and one great answer choice.

I hope this helps, and I wish you all of the luck in your studies.

Best,
Ryan

Thank you Ryan! That makes a lot of sense

[teddykim100]

More of a general question but, doesn't the answer assumption required attack the validity of our premise?

Our argument core is:

earliest bird fossils discovered date back tens of millions of years than oldest known dromeosaur fossils => therefore, paleontologists' claim is false

the premise of "the earliest bird fossil dating back tens of millions of years" is then missing an assumption to reach our conclusion, an assumption which if left untrue, would attack our premise's truth, rather than attack the connection between premise and conclusion

[Luke Haqq]

Hi teddykim100!

Your reasoning sounds correct.

If you have PowerScore's course books, on this point you might find Lesson 5 useful. Specifically at page 5-2, that lesson discusses Supporter versus Defender assumptions. The latter eliminate ideas or assertions that would undermine the conclusion, which is what answer choice (D) does on this question. Answer choice (D) affirms that the fossils that have been found actually indicate the relative dates of those fossils, eliminating possibilities such as the implications of other fossils that haven't been found yet.