Compare expressions involving the same general subject but different targets of judgment.
Singular: “Zayd is human” — one determinate person.
Natural: “Human is a species” — the universal nature itself.
Quantified: “Every human is an animal” — explicitly every instance.
Indefinite: “Humans err” — a judgment about individuals but no stated quantifier.
Both quantified and indefinite forms can have a universal subject and concern its instances. In quantified propositions the range is explicit; in indefinite ones it is not stated in the form.