Critic: An art historian argues that because fifteenth century European paintings were generally more planimetric (that is, two-dimensional with no attempt at suggesting depth) than were sixteenth-century paintings, fifteenth-century painters had a greater mastery of painting than did sixteenth-century painters.
Conclusion
(This art historian's conclusion is wrong) 15th century painters did not have greater mastery of painting than 16th century painters.
Evidence
The historian believes this because 15th century were more planimetric, but "how planimetric a painting is" has nothing to do with whether you have greater mastery.
Evaluate
This is one of the top 5 famous flaws, but it's always so subtle when it happens. You have to distinguish between two types of rebuttal conclusions: - their conclusion is unwarranted - their conclusion is false
This author is allowed to conclude the first, but not allowed to conclude the second.
John thinks that Megan likes him because she kissed him on the cheek when he arrived at her apartment. But Megan kisses all her friends and acquaintances on the cheek (because she spent a semester in Europe and came home insufferable).
The valid conclusion here is,
A going-too-far flawed conclusion here is, (i.e. Megan doesn't like John)
We can't conclude she doesn't like him. Maybe she does. Where's our evidence she doesn't?
We call this famous flaw Unproven vs. Proven False (you may also have heard it called Absence of Evidence or Failure to Prove).
This author showed that the art historian's premise was irrelevant. But that doesn't mean the art historian's conclusion is wrong.
Goal
Look for an answer pointing out the Unproven vs. Proven False move, or raising the objection that there might be some other reason to consider 15th century painters' having more mastery.