Presumably, that it can't be detected, even indirectly, with the mind or senses. I don't know for sure if that's the sense they meant it in, but I also can't think of any other potential meaning.First of all, emotion and thought are both just the brain observing itself. Other peoples' happiness can also be observed and even studied; it belongs to the scientific fields of neurology and psychology, as well as the philosophical field of aesthetics.Happiness can't be "observed"I don't understand how "observing parts of history" is distinct from "observing history" or how being artificially constructed prevents something from being observed.History can't be "observed", so does it not exist? Sure, we can look at pictures, read old books, excavate ruins; those are all parts of history, but history itself is a construct.
To be clear: I wasn't asserting that gender is unobservable; I was expressing befuddlement that Purple Eagle's link defined it that way.
EDIT: That's a contradiction. If something is "obvious" to you, that's because you're observing it.