In The Foundations of Arithmetic (§ 48, p. 61), after maintaining that statements of numbers are indeed statements of fact, Frege asserts that:
The concept has a power of collecting together far superior to the unifying power of synthetic apperception. By means of the latter it would not be possible to join the inhabitants of Germany together into a whole; but we can certainly bring them all under the concept "inhabitant of Germany" and number them.
What I find troubling and hard to understand is this part - By means of the latter it would not be possible to join the inhabitants of Germany together into a whole. Why? Is Frege criticizing transcendental apperception whilst ignoring empirical apperception? If his critique is that of empirical apperception, I can't say I understand the highlighted text at all. I've come to believe that he merely wants to state that the concept is a much better tool and that I'm probably looking way too much into it.