Elementary particles are viewed as linearized excitations of a nonlinear massless Dirac field, whose ground state is assumed to contain a finite density of field quanta. Nucleons and antinucleons are viewed as single-particle and single-hole excitations, and other elementary particles as space-symmetric correlations of 2, 3, or 4 particles and holes. Hyperons are viewed as composite. The strangeness quantum number is identified with half the excess of particles over holes in the excitation. The classification has room for 29 particles: the known elementary particles plus doubly charged K and μ mesons and antiparticles, a strange charged spin 1 boson and antiparticle, and a boson quintet of strangeness and charge 0, +/-1, +/-2.