Logical Reasoning

PT21 · S3 · Q13 One of the effects of lead poisoning

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One of the effects of lead poisoning is an inflammation of the optic nerve, which causes those who have it to see bright haloes around light sources.

Conclusion

It's likely that Van Gogh was suffering form lead poisoning caused by ingesting the pigments he used.

Evidence (since)

Van Gogh painted bright haloes around the stars and sun in his later paintings. He used a pigment in "Sunflowers" that had lead, and one effect in lead poisoning is that you see bright haloes around light sources.

Evaluate

This argument is trying to Explain a Curious Fact: why are there bright haloes around the stars and sun in Van Gogh's later paintings?

The author explains it this way: Van Gogh used a yellow paint when he made "Sunflowers" that had Naples yellow, a pigment that contained lead, so he ended up getting lead poisoning, which causes people to see bright haloes around light sources, so he ended up painting bright haloes around light sources in his later paintings because that's how they looked to him in real life.

Whenever we encounter Explain Curious Fact arguments, we have two central lines of inquiry:

- could there be some Alternate Explanation for the curious fact? - how plausible is the Author's Explanation?

Goal

Since this is Necessary Assumption, the correct answer should either - rule out an Alternate Explanation for the bright haloes in Van Gogh's later paintings (e.g. )

or

- provide something that's necessary to the plausibility of the Author's Explanation (e.g. )

13.

Which one of the following is an assumption on which the argument relies?

  1. Correct

    In Van Gogh’s later paintings

    Why this is right

    This is providing an idea that is necessary for the author's explanation to be plausible. In her mind, Van Gogh has lead poisoning in his later years, and so he sees bright haloes around light sources and thus paints bright haloes around light sources in an attempt to make his painting match what he sees. So she is assuming that at least sometimes he painted things as he saw them. If we negated this answer, that would mean "in his later paintings, Van Gogh never painted things as he saw them". Would that negation weaken the argument? Definitely! So this should be correct. If he never painted things as saw them, and he painted bright haloes around the stars and the sun, then that means that does not see bright haloes around the stars and the sun, which suggests that he did not have lead poisoning. If it's easier, you can think about the negation (he never painted things as he saw them) as weakening by providing an alternate explanation: there weren't bright haloes because that's what his lead-poisoned vision made stuff look like -- he wasn't even painting what he saw -- there were haloes purely because of his artistic purposes.

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

    70% picked this

  2. Van Gogh continued to use

    Not Necessary

    While it could strengthen the author's argument if we knew that Van Gogh had ongoing lead exposure, it's not necessary. He definitely had exposure to lead. The author needs to assume that he had enough exposure to trigger lead poisoning, but it's highly possible that this sufficient exposure to lead occurred purely through his work on "Sunflowers". The author doesn't need to assume that he had ongoing lead exposure.

    9% picked this

  3. Van Gogh did not have

    Out of Scope: other symptoms

    Whether Van Gogh had other symptoms or only had halo-vision, it wouldn't make any difference to this argument. This argument is definitely assuming that Van Gogh had at least one symptom from lead poisoning (seeing bright haloes around light sources), but it doesn't need him to have only one symptom.

    4% picked this

  4. The paints Van Gogh used

    Too Strong: no other

    It doesn't make any difference to this argument whether the paints used in "Sunflowers" had other toxic ingredients. It would only matter if those other toxic ingredients also could explain bright haloes around light sources. And we have no common sense reason to think that toxic ingredients generally cause bright haloes, so if we negate this and get, "Yo author -- there were other toxic ingredients in the paints he used", it would be a very weak objection because we have no reason to think that those other ingredients would be an Alternate Explanation for the bright haloes.

    11% picked this

  5. The effects of Naples yellow

    Too Strong

    Too Strong: could not have been achieved This answer is saying that Naples yellow was the only pigment that could achieve a certain effect. We don't have any restrictive language like that in the paragraph. We just know that Van Gogh used Naples yellow; we don't know he had to use it to achieve a certain effect.

    6% picked this

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