  We will present a collection of guessing principles which have a similar
relationship to $\diamond$ as cardinal invariants of the continuum have to
$\CH$. The purpose is to provide a means for systematically analyzing
$\diamond$ and its consequences. It also provides for a unified approach for
understanding the status of a number of consequences of $\CH$ and $\diamond$ in
models such as those of Laver, Miller, and Sacks.
