Logical Reasoning

PT111 · S1 · Q17 On the basis of the available

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On the basis of the available evidence, Antarctica has generally been thought to have been covered by ice for at least the past 14 million years.

Conclusion (therefore)

About 3 million years ago, the Antarctic ice sheet must have temporarily melted.

Evidence (after all)

We recently discovered 3 million year old fossils under the ice sheet covering central America (previously we had only found this type of fossils at the bottom of the ocean).

It's plausible that Antartica could have been submerged under water, since severe climate change or volcanic activity could have melted the ice sheet.

Evaluate

Since the author is looking at a puzzling piece of archaeological evidence and speculating what it means / what it tells us, we can use our Curious Fact / Explanation mindset.

Curious Fact ... why are we finding these 3 million year old fossils under the ice sheet covering Antartica? (Previously we had only found these fossils in ocean floor sediments)

Author's Explanation ... At the time of these fossils, the ice sheet must have been melted, which would raise the water level high enough that Antarctica would be underwater, and so the ocean creature these fossils are from would have been swimming "over" Antarctica, it would have died and sunk to the "ocean floor", which would have been the top of Antarctica, and then later as the water refroze and the continent again rose above sea level, those fossils would be trapped under the ice sheet.

Evaluate

Notice how many blanks we had to fill in for the author just to understand her Causal Story! (I'm not even 100% sure I'm interpreting her causal story correctly)

When Flaw intersects with Curious Fact / Explanation arguments, the most common type of correct answer just calls out the fact that the author is overconfidently assuming one possible causal interpretation of the evidence, when others exist.

When we simply say we're saying,

Our author's conclusion is way too strong --- the ice sheet must have temporarily melted?

There aren't any other explanations? If we assumed that Antarctica did not melt and was still above sea level, can we think of any other possible way that the fossils could have ended up where we found them?

Sure, maybe a bird snatched this fish out of the ocean and was flying over Antarctica and dropped it. Maybe a hurricane or an underwater volcano lifted this fish into the air and flung it over Antarctica. Maybe within the ice sheet there used to be underwater tunnels that this fish could have gone through. Maybe this fish was really an amphibian that was able to scoot across the ice.

Goal

When we're doing Flaw and read one of these Curious Fact / Explanation arguments, then we're receptive to three different types of answers: 1. Complain that the author is overly confident in arriving at one possible explanation, where others may exist.

2. Suggest that the author may have failed to consider some alternative explanation.

3. Point out something implausible about the author's explanation.

17.

The reasoning in the argument is most vulnerable to which one of the following criticisms?

  1. That a given position is

    Bad Premise Match

    Because of this answer's structure "that X is taken show that Y" means that X is supposed to refer to Evidence and Y to the Conclusion. In this argument, "Chris is a boy. Thus he must like football", we could say that the flaw in this argument was this: that Chris is a boy is taken to show that he is a football fan So does this answer choice match up with our argument? Was there a premise that said a given position is widely believed to be true? No, there was a background claim that said it's widely believed to be true that "Antarctica was covered by ice for the past 14 million years". Did the author conclude that this claim must be true? No, the opposite. Her conclusion is actually saying it must be false, that the ice sheet must have temporarily melted 3 million years ago.

    5% picked this

  2. That either of two things

    Bad Premise/Conclusion Match

    This has the same structure as (A), so we're trying to match the first half with the evidence and the second half of the conclusion. Did the evidence say that "either of two things could have independently produced a given effect"? Sure, it said that either volcano or climatic warming could have independently produced a melting of the ice sheet. Does the conclusion then say that, "those two things could not have operated in conjunction to produce that effect?" No. The conclusion just says "that effect must have occurred" (the ice sheet must have melted) This answer would hurt an argument that sounded like this: Bernadette's perfume and Bernadette's dress each would made Tyrone attracted to her. Thus, Tyrone was not attracted to the combo of her perfume and her dress.

    9% picked this

  3. Establishing that a certain event

    Bad Description

    The author is trying to establish that a certain event occurred (the ice sheet temporarily melted 3 million years ago). The author brings up a couple causal possibilities for how that would have happened, although the primary evidence for it having happened is the fossils discovered under the ice sheet. This answer is saying, "Just because we know the event occurred doesn't mean we know that caused the event". That objection wouldn't be relevant to the author's argument since she isn't claiming to know what caused it (bring up possible things that could have caused it is not claiming to know what one thing did cause it). We might re-write this answer as a more successful one by saying, establishing that things could have cause an event is confused with establishing that the event actually occurred But it would still be a poor answer because the author's primary evidence are the fossils, not his ruminating about what what might have caused the ice sheet to melt.

    23% picked this

  4. A claim that has a

    Wrong Flaw

    This refers to the famous Sampling Flaw, but we can't match that to this argument. Could we call the conclusion "a claim that has a very general application"? Not really -- the conclusion is a specific claim that "about 3 million years ago, the ice sheet temporarily melted".

    5% picked this

  5. Correct

    An inconsistency that, as presented,

    Why this is right

    "X is treated as though Y" indicates that X is our evidence and we treated it as though it shows that our conclusion Y is true. Did the evidence feature an inconsistency that, as presented, has more than one possible resolution? Sure, we found fossils under an ice sheet that had previously only been found in ocean-floor sediments. The place we found these new fossils is inconsistent with the place where we have previously always found this type of fossils. Does the author treat this as though only one resolution is possible? Yes, she concludes that the ice sheet must have melted (i.e. this part of Antarctica must have been underwater at the time this animal died). Is there more than one possible resolution? Yes, as discussed before, maybe a bird dropped it, maybe a hurricane flung it, maybe it was amphibian and crawled there, maybe it swam through an ice sheet tunnel, etc. If we wanted to customize this to our vernacular, this answer is just saying "A Curious Fact that, as presented, has more than one possible explanation is treated as though only the author's explanation is possible."

    Skill tested: Flaw · how this choice captures the argument's function is the move to repeat next time.

    58% picked this

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