The Arabic Alphabet (Part 2)

How can Semitic writing (Phoenician, Arabic, and Hebrew, etc.) function well when vowels are omitted?

It can because consonants and vowels have different roles in a Semitic language.

The root is a group of (usually) three consonants. The vowels spoken with the consonants are not part of the root:

KTB (katab) = write
KLB (kalb) = dog
WZN (wazn) = weigh

Each consonant group leads the reader to only one basic idea. There cannot be totally different meanings for one consonant group, as there are in English. For instance, in English, HT might be hot, hate, hit, hut, hat, or hoot.

Semitic vowels carry subsidiary information that can usually be gleaned from the context:

KaTaBa = he wrote
KuTiBa = it was written
KuTuB = books

So all three of these words can be written KTB without ambiguity, in most contexts.

(Below) Most Arabic letters have four variant forms, the choice of which depends on where they fall: at the beginning or end of a word, within a word, or alone.