Methods used up to that time had depended heavily on the well-ordering principle which Zermelo had proposed in 1904, namely that every set can be well-ordered.
Mga pamamaraan na ginagamit hanggang sa panahon na nagkaroon depended mabigat sa well-order sa prinsipyo na Zermelo had iminungkahing in 1904, namely na ang bawat set ay maaaring maayos.