@Reconstructo,
I'm afraid my answer would have to be the rather dry one (at least at first sight) that Frege was right about this, in sections 54 and 55 of his
The Foundations of Arithmetic.
However, I find at least one crucial passage in section 54 obscure. In the second, long paragraph, after the main thesis of this section, which is that it would be a good idea to "call a concept the unit relative to the Number which belongs to it", he immediately goes on to try to make some sort of distinction between what might be called (although he does not use the terms) discrete and continuous concepts. Although I appreciate the need for some such distinction, I find his version of it unintelligible. (This admission may prompt me to have another go at understanding it.)
Section 55, defining (among other things) what it means for the number 1 to belong to a concept - he later goes on to explain that this does not yet define the number 1 as an object - raises (as does Russell's theory of definite descriptions) the question of what it means for two things to be "the same" or "equal" or "identical" - but let's leave that question for the thread with the title "The same"!