During the 1980’s Japanese collectors were very active in the market for European art, especially as purchasers of nineteenth-century Impressionist paintings.
Conclusion (this surely reflects = opinion)
Many Japanese collectors preferred certain aesthetic attributes of 19th century Impressionist paintings.
Evidence
During the 1980's Japanese collectors were very active in the market for European art, especially buying up 19th century Impressionist paintings.
Evaluate
Since the author is interpreting the meaning behind a group of people's behavior, we can use our Explain Curious Fact mindset.
Curious Fact ... Why were these Japanese collectors so interested in buying 19th century Impressionist paintings?
Author's Explanation ... They had a preference for certain aesthetic attributes found in those paintings.
We always analyze this framework by asking the same two questions: 1. Could there be some Alternate Explanation for the curious fact? 2. How plausible is the Author's Explanation?
Goal
We can strengthen by ruling out an alternate explanation for why Japanese collectors were so interested in buying 19th century Impressionist paintings (they weren't buying them just to turn around and re-sell them at a profit / they weren't buying them just to acquire famous art to enhance their status despite not really liking the paintings aesthetically).
Or we can strengthen by adding plausibility to the idea that these Japanese collectors really dug certain aesthetic properties of 19th century Impressionist paintings.