Large pore defects clearly develop in Al2O3 ceramics during sintering, These large pores originate from voids caused by the incomplete deformation and adhesion of powder particles in collapsed dimples at the centers and boundaries of granules in the green compacts. The coalescence of pores, with limited shrinkage, during densification and grain growth in the late intermediate to final stages of sintering, is considered responsible for the development of the large pores. The mechanism of pore coalescence is explained by thermodynamic arguments, which demonstrate that the largest pores result in a stable system.