Logical Reasoning

PT142 · S4 · Q4 Paleontologists had long supposed that

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Paleontologists had long supposed that the dinosaur Diplodocus browsed for high-growing vegetation such as treetop leaves by raising its very long neck.

Conclusion (Thus)

Diplodocus must have fed on plants on or near the ground, or underwater.

Evidence

Diplodocus had neck bones that would prevent it from raising its very long neck to browse for high growing vegetation.

But the neck could bend downward and even extend below ground level, letting Diplodocus dip its head underwater and reach underwater vegetation, while still standing on land.

Evaluate

This doesn't feel like an Internal Math / Missing Link type of argument, so we should probably switch into Debate mode.

Given that ... Diplodocus couldn't reach high leaves by raising its long neck,

How can we argue that ... it didn't feed on ground level or underwater plants?

It seems like we may be dealing with a False Choice here, because the argument went from . Is it possible they ate medium height leaves?

We have to assume that raising their neck was the only way for them to eat the high leaves. Maybe they could have just kicked the bark of a tall tree and waited for the leaves to fall off into their mouths.

We have to assume it's feasible that they fed on ground level or underwater plants: were there plants near the ground or underwater that were available and part of this dino's diet?

Was there anything dangerous or physically hard about the act of eating food that low?

Goal

We should probably go looking for an answer that, if negated, would weaken.

The correct answer, when negated, should help us say,

4.

Which one of the following is an assumption required by the argument?

  1. The same type of neck

    Too Strong: same

    This would definitely strengthen the plausibility of the author's conclusion, but it's not needed for the conclusion to be true. Negating it has almost zero weakening effect. Even if Diplo's neck didn't have an identical structure as modern ground-feeding animals, it could still certainly have been a ground-feeding animal.

    2% picked this

  2. Diplodocus was not able to

    Too Strong: unless / sharply

    This would definitely strengthen the plausibility of the author's story that Diplo spends most of its life looking towards the ground / looking underwater, but it's not needed for the conclusion to be true. Negating it has almost zero weakening effect. If Diplo could still see in front of itself even when its head was angled mildly downward, does that badly weaken the argument? Not at all.

    2% picked this

  3. It would be impossible for

    Too Strong: impossible

    This would definitely strengthen the notion that Diplo is not spending most of its life with an elevated brain up at the tree top foliage (it would lose blood supply to its brain if it lived that way). But it's not needed for the conclusion to be true. Negating it has almost zero weakening effect. If we say that it would be possible for such a large animal to supply blood to an elevated brain, that doesn't weaken the argument. Even if the brain's blood supply could handle tree-top eating, we've already been told that Diplo's neck bones cannot handle tree-top eating.

    0% picked this

  4. Correct

    Diplodocus had no other way

    Why this is right

    We always find it inviting when a Necessary Assumption answer choice is ruling out an idea using "not / no". They are easy to negate and the best use of the negation test. Would it hurt the argument if we said that Diplo did have some other way of accessing high-growing vegetation? Yes! The author assumes that since its neck wouldn't allow it to raise to the tree-tops, then it didn't consume tree-top foliage. We half-jokingly considered the objection that maybe it could kick the tree and that high foliage would come raining down, allowing Diplo to reach it. This answer is saying that Diplo would rise up on its hind legs. If you picture a dog standing on its hind legs, and reaching its paws up to your stomach, the dog's body orientation is now perpendicular to how it was. It was parallel to the floor, and now it's parallel to your body. It's almost like your body is now the floor, relative to the dog. If you picture a dinosaur doing that to a tree, the dinosaur would be oriented to the tree in a way that's similar to the dinosaur being oriented to the ground in normal walking conditions. Bending low to eat what's right in front of its front legs would now be the tree-tops (whereas if it were on ground, the same motion would involve eating ground-level or underwater plants right in front of its front legs). We don't need to get this full visual, because this answer isn't even committing to that specific alternate method. This answer is just saying the author assumes that, "If Diplo can't raise its very long neck to reach tree top vegetation, then Diplo cannot feed on tree top vegetation", which assumes that there aren't any other ways to feed on tree top vegetation.

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

    90% picked this

  5. Diplodocus was not able to

    Weakens-ish

    This also has the lovable ruling out "not" form, but this negation doesn't weaken. If we say that Diplo was able to browse for underwater vegetation by kneeling beside the water or walking into the water, that doesn't pose any objection to the conclusion that "Diplo fed on plants near the ground or underwater". In fact it just strengthens that conclusion by providing evidence of more ways in which Diplo could access that food.

    6% picked this

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