  Highly acurate numerical simulations are employed to highlight the subtle but
important differences in the mechanical stability of perfect crystalline solids
versus amorphous solids. We stress the difference between strain values at
which the shear modulus vanishes and strain values at which a plastic
instability insues. The temperature dependence of the yield strain is computed
for the two types of solids, showing different scaling laws:
$\gamma_{_{Y}}\simeq \gamma_{_{Y}}^{0}-C_1 T^{1/3}$ for crystals versus
$\gamma_{_{Y}}\simeq \gamma_{_{Y}}^{0}- C_2 T^{2/3}$ for amorphous solids.
