In this paper we deal with the problem, whether number is a property of external things. It is divided into three parts. Firstly Mill’s empiristic concept of natural numbers is summarized, then Frege’s arguments against this conception are put forth and finally viewpoints of some contemporary analytical philosophers (first of all G. Kessler), who reject Frege’s critique, are set out. Kessler and his followers in fact revive the abandoned theory of Mill.