In his paper Two notes on the foundations of set-theory, Kreisel begins:
Recall that, naively, sets present themselves in a number of distinct contexts. [...] One may therefore doubt whether any definite general notion (of set) is involved here; it look[s] much more like a mixture of notions. As a matter of historical fact this was the common feeling among Cantor's contemporaries.
Kreisel does not give a source for the emphasized claim. My question is whether in fact this is accurate.
One possible difficulty, at least in looking for sources slightly pre-Cantor, is likely to be that insofar as that was the common feeling there may not be much positive evidence of that - if nobody sees a particularly unified conception of X, there's no obvious impetus to say so. However, I'm still hopeful.