 Cardinal numbers are the numbers that can be used to answer the question ‘How many \(\ldots\) are there?’, and Frege discovered that such numbers bear an interesting relationship to the natural numbers. Frege’s insights concerning this relationship trace back to his work in Gl, in which the notion of an extension played very little role. The seminal idea of Gl §46 was the observation that a statement of number (e.g., “There are eight planets”) is an assertion about a concept. To explain this idea, Frege noted that one and the same external phenomenon can be counted in different ways; for example, a certain external phenomenon could be counted as 1 army, 5 divisions, 25 regiments, 200 companies, 600 platoons, or 24,000 people. Each way of counting the external phenomenon corresponds to a manner of its conception. The question “How many are there?” is only properly formulated as the question “How many \(F\)s are there?” where a concept \(F\) is supplied. On Frege’s view, the statements of number which answer such questions (e.g., “There are \(n\) \(F\)s”) tell us something about the concept involved. For example, the statement “There are eight planets in the solar system” tells us that the ordinary concept planet in the solar system falls under the second-level numerical concept being exemplified by eight objects. 