5.47 It is clear that everything that can be said generally in advance about the form of all propositions must be able to be said all at once.
Indeed all logical operations are already contained in an elementary proposition. Because “fa” says the same as “(Ex). fx. x=a.”
Where there is complexity [compoundness] there is argument and function, and where these are, are already all logical constants.
One could say: the one logical constant is that which all propositions by their nature have in common with one another.
That though is the general propositional form.
So really there is no true logical constant, or this line of inquiry has misconceived the nature of logical constants.