  The possibility that leptons, quarks or both might be highly relativistic
bound states of a spin-0 and spin-1/2 constituent bound by minimal
electrodynamics is discussed. Typically, strongly bound solutions of the
Bethe-Salpeter equation exist only when the coupling constant is on the order
of or greater than unity. For the bound-state system discussed here, there
exist two classes of boundary conditions that could yield strongly bound
solutions with coupling constants on the order of the electromagnetic fine
structure constant. In both classes the bound state must have spin one half,
thus providing a possible explanation for the absence of higher-spin leptons
and quarks.
