Classical Adûnaic consonants can be classified into groups by their method of pronunciation. These continuants (consonants for which the flow of air is continuous) are mostly survivals of Primitive Adûnaic continuants (SD/418). The continuants were frequently unvoiced in cases where they appeared after voiceless consonants (spirants, [s] and [h]) as well as sometimes before [s] and [h] (SD/421-2), but these unvoiced sounds were probably allophones of the voiced sounds with no changes in the spelling, with the possible exception of [z] (Tolkien’s notes are unclear).