To get to the heart of this matter we must resort to some subtle reasoning methods, more powerful than those of propositional logic. Predicate Logic Propositional logic is very useful but often too weak in terms of its expressive power. In essence, propositional logic deals only with connections between propositions. Predicate logic is a more general formalism with more expressive power. Some student drinks.
All students drink.
Predicate logic analyzes connections between such sentences. If some student drinks, then all students drink. If all student drinks, then some student drinks. These two sentences have the same propositional structure, but one of them is true and the other false. A more detailed analysis is needed.