A quantifiable majority determines the outcome of an unknown, as per the biblical verse: "Follow the majority." But with an unquantifiable majority - what is the source for the principle to apply in those cases as well? Note that the Gemara supports this principle with 9 examples -- that is, 9 sources as possibilities from which it is understood or derived. Note also that checking the reality of the situation isn't the issue; the sages are intent on establishing the sources and using the majority to establish "truth," rather than looking for the truth in other ways.