I mentioned Frege's distinction between concept and object earlier, and said I was taking a feature of that distinction as fundamental, namely that the distinction between predicate and sentential negation only applies to concept words (or rather, quantified concept words), and not to object words ('logical subjects').
David Brightly wasn't so sure it was a feature of that distinction, as opposed to a mere accident. Well, two further reasons. First, it is build into the predicate calculus that simple singular propositions have only one form of negation. We write '~Fa'. The syntax of the calculus is designed so that we cannot even represent the difference between 'Socrates is not running' and 'it is not the case that Socrates is running'.
Second, Frege begins his discourse by saying that a concept is predicative, whereas the name of an object, a proper name, is quite incapable of being used as a grammatical predicate. Now, we can say that someone is Alexander the Great, or is the planet Venus, but this is not predicating the object itself. For the predicate 'is the planet Venus' is predication not of Venus itself but of the concept of being identical with Venus. The verb 'is' is not a mere copula, its content is an essential part of the predicate.
Thus for an object-word to signify, it has to signify an object. It is essential to an object word like 'Venus' that it has to be satisfied, whereas it is essential to a concept word like 'planet' that it can be satisfied, or not. "An equation is reversible; an object's falling under a concept is an irreversible relation.
Thus "‘Venus exists’ is true in virtue of the meaning of the proper name ‘Venus’. Maverick says that this has it precisely backwards. What I should say is that 'Venus' has meaning in virtue of the truth of 'Venus exists'. Not at all. 'Venus' has meaning in virtue of its meaning something, just as you are an employer in virtue of your employing someone.