Three correlationships are established among the optical dielectric constant epsilon(infinity), Szigeti effective charge e(s)*, transition temperature T(c), melting temperature T(m), and optical phonon frequency for many cubic fast ionic conductors. These relations suggest an intense influence of electronic energy state near the band gap to the origin of fast ionic conduction, dominant contribution of short-range or long-range forces to the mobile ion below T(c) or to the cage ion above T(c). A curious temperature dependence for epsilon(infinity) and e(s)* values is also interpreted by considering anharmonic dynamical effective charge.