  The values of $\sin (2 \alpha)$ and $\sin (2 \beta)$, where $\alpha$ and
$\beta$ are angles of the unitarity triangle, will be readily measured in a B
factory (and maybe also in hadron colliders). We study the standard model
constraints in the $\sin (2 \alpha) - \sin (2 \beta)$ plane. We use the results
from recent analyses of $f_B$ and $\tau_b|V_{cb}|^2$ which take into account
heavy quark symmetry considerations. We find $\sin (2 \beta) \geq 0.15$ and
most likely $\sin (2 \beta) \roughly{>} 0.6$, and emphasize the strong
correlations between $\sin (2 \alpha)$ and $\sin (2 \beta)$. Various schemes
for quark mass matrices allow much smaller areas in the $\sin (2 \alpha) - \sin
(2 \beta)$ plane. We study the schemes of Fritzsch, of Dimopoulos, Hall and
Raby, and of Giudice, as well as the ``symmetric CKM'' idea, and show how CP
asymmetries in B decays will crucially test each of these schemes.
