The analysis of the concept of number is indeed the ultimate goal of Frege's scientific program, already stated in the Vorwort of the Begriffsschrift. We begin by considering Frege's negative statements about numbers; numbers are neither external things nor subjective entities. This is an opportunity to see an interesting limitation in Frege's system of concepts: he is not clear about subjective. This is why the dichotomy mentioned above (external thing-subjective) is not capable of covering all past philosophies of number. Something like transcendental subjectivity should be taken into account (10.1).