In short, the clear impression in the immediate period leading up to Zermelo's work was both that only the WOH would provide a solid foundation on which to build a reasonable notion of infinite cardinal number as a proper framework for tackling CH, and that WOH requires justification, that it must become, in effect, the WOT, the WO-Theorem. In short, establishing the WOT was closely bound up with the clarification of what it is to count as a set.