Expressions like “1 is a number,” “there is only one number nought,” and all like them are senseless.
(It is as senseless to say, “there is only one 1” as it would be to say: 2 + 2 is at 3 o’clock equal to 4.)
The formal concept is already given with an object, which falls under it. One cannot, therefore, introduce both, the objects which fall under a formal concept and the formal concept itself, as primitive ideas. One cannot, therefore, e.g. introduce (as Russell does) the concept of function and also special functions as primitive ideas; or the concept of number and definite numbers.