One adjective paired with multiple nouns

Question

Perhaps trees feel things in a way totally different from us, but we have no way of finding out about it, because we have no way of discovering the correlations between experience and observable manifestations or physical conditions in their case. We could discover such correlations only if we could observe both the experiences and the external manifestations together

[What does it all mean?, Thomas Nagel, p.26]

Does the word "observable" modify both "manifestations" and "physical conditions" or it just modifies "manifestations"?

Answer 1

The scope of the adjective "observable" seem ambiguous at first, but it looks to me as if "observable manifestations" is what is intended. In fact, "observable" means something similar to "manifest", so it's sort of redundant.

I think "physical conditions" is intended to be in contrast to what is observable, the point being that we have no way of correlating "experience" with either "observable manifestations" or with "physical conditions" that aren't observable.

That is all debatable, but it doesn't make much difference; the main point of the passage is the inaccessibility of the tree's putative "experience".