[cyclopeanutopia]

> At what point did it become a thing?

Early on and for obvious reasons - it is pretty easy to observe in oneself, much easier than discovering electrons. ;)

[bawolff]

But its also pretty hard to observe in others, which makes it hard to come up with a satisfying definition. Without a concrete definition, you can't really do science with it.

[david-gpu]

Alan Wallace wrote a short essay on this subject titled The Taboo of Subjectivity. It is available online for free, if you are curious.

[cyclopeanutopia]

Yes, but that's exactly what I meant - the idea is prescientific.