At 15:34 -0500 2003-03-03, John Cowan wrote:

>Abjads represent consonants with full letters, and use optional diacritics
>to represent vowels.

They needn't be diacritics per se, I would think.

>1) If a script makes its vowels optional, but uses full letters for them, is
>it an abjad?

I would think so.

>2) If a script uses diacritic vowels, but requires them, is it an abjad?

No. Thaana and Quenya-mode Tengwar are alphabets.
--
Michael Everson * * Everson Typography * * http://www.evertype.com