Mutes are those
consonants that are pronounced with a stoppage of the
breath. Some have no vocalization at all, e.g., the
breathed consonants π,
τ, and κ.
Others, β, δ,
and γ, are voiced. Still, there is
that stoppage. Early on, the rough mutes were
aspirates, apparently pronounced as a combination of
a stopped consonant and an "h" sound.
Although it is thought that the sound of these rough
mutes softened in Hellenistic Greek, they are still
categorized among the mutes. The following matrix
shows the categorization of mutes into three classes
and three orders.