If the four basic parameters to define seismic design forces, i. e. seismic shear, seismic shear coefficient, seismic force and seismic coefficient, are defined as functions of normalized weight, the relationships between these parameters are mathematically given. A uniform shear type elastic body fixed at the base is analyzed in order to explain the base shear and the distribution of the shear along the height of a building. Lumped mass systems are also analyzed and the formula to give an appropriate distribution of seismic shear was proposed. Tower-on-a-base type buildings, whose base shear and the distribution of the shear are very different from those of the other types of buildings, are analyzed. Finally, the design method for a tower-on-a-base type building is proposed.