Are all hadrons alike?

Using the existing knowledge of the chromodynamic vacuum as a basis we investigate mesons built from u, d, s quarks and/or gluons. A new classification of hadrons is proposed which reflects the strength of interaction of various currents with vacuum fields. It is found that the mass scale intrinsic to the resonance structures in different channels is not universal; a large mass scale is discovered, for instance, in the 0^-, 0⁺ gluonic channels. Starting from our classification we establish the hierarchy of scales. Regularities of the hadronic phenomenology [Zweig's selection rule, approximate SU(6) symmetry and so on] are naturally explained. The properties of glueballs are discussed in some detail. A few low-energy theorems are derived, which imply, in particular, a new mass relation for the η′ meson.