Here we have an instance of a kind of polarity which belongs to the fundamentals of nature as much as does the levity-gravity polarity itself. Wherever two poles of a polarity meet, they have the possibility of being connected in two ways which in themselves are again polarically opposite. Our further studies will bring up various other instances of this kind, and will show us that part of the epistemological trouble in which science finds itself to-day results from the fact that the scientific mind has been unable to distinguish between the two kinds of polarity - that is, as we shall say henceforth, between polarities of the first order (primary polarities) and polarities of the second order (secondary polarities).