Writing Systems of the World 5, Exercise 1: how an abjad works

In a Semitic language the core meaning sits in a root of usually three
consonants (K-T-B, "write"), while the vowels mark the grammatical form:
kataba "he wrote", yaktubu "he writes", maktabah "library" (Abjad article).
A reader who knows the language sees K-T-B in context and supplies the right
vowels.

English is a worse fit because its vowels carry a lot of the distinction
between words (my own example: "bat", "bet", "bit", "bot" and "but" share the
consonants b-t and are all different words), so a consonant-only spelling
would leave too many words ambiguous without help.