A correlation between Young's modulus, as determined by using nanoindentation atomic force microscopy (AFM), and atomic polarizability is observed for members of a series of cocrystals based on systematic changes to one cocrystal component. Time domain spectroscopy over terahertz frequencies (THz-TDS) is used for the first time to directly measure the polarizability of macro- and nanosized organic solids. Cocrystals of both macro- and nanodimensions with highly polarizable atoms result in softer solids and correspondingly higher polarizabilities.