# Why are alkoxides strong bases?

For the same reason that hydroxide, $H {O}^{-}$, is a strong base.
Alkoxides, $R {O}^{-}$, are clearly akin structurally and electronically to hydroxide anion. $H {O}^{-}$ and $R {O}^{-}$ have the same valence, electronic structure.
The charge on an alkoxide is localized to an oxygen centre. Moreover, the alkyl groups are formally electron releasing, and pump in electron density to this electronegative site. The result? $R {O}^{-}$ is a powerful base, and a powerful nucleophile.