If a crystalline material possesses a center of symmetry, it cannot be ferroelectric. Also, its Raman active modes must occur at different frequencies from its infrared (IR) active modes; this is the Exclusion Principle. By studying single crystals and ceramics, we have determined the Raman and IR active phonon frequencies for atomic motion along the c-axis in YBUO,b,O th in the superconducting and semiconducting phases. The measured phonon frequencies are consistent with the Exclusion Principle, hence this material does not appear to be ferroelectric in either the superconducting or semiconducting phases. © 1990, Taylor & Francis Group, LLC. All rights reserved.