The Hebrew and Arabic alphabets are derived from the Phoenician alphabet.  Phoenician was a language spoke in Tyre, Sidon, and Carthage and its colonies in North Africa, Sicily and Spain.  Arabic was not derived directly from Hebrew, but it is apparent that the inventors of Arabic writing were aware of Hebrew, because certain features could hardly have another explanation.

Just as Hebrew inscriptions antedate the earliest known exemplars of the Bible, to wit, those contained among the Dead Sea Scrolls, by several centuries, so do Arabic inscriptions antedate the Qur’an, but only few, if any, of these are in the Arabic script familiar today.

The Hebrew alphabet consists of 22 letters, 5 of which have special word-final variants, and writing proceeds from right to left.  The so-called square script, pictured at the above link and familiar to anyone who has passed Jewish places of business, is a post-Biblical decorative innovation.  The original Hebrew script, pictured here in the Dead Sea Scrolls is much simpler, lacking the graceful brush strokes of the square script and resembling English hand-printed lower-case letters.  There is also a third version, called cursive Hebrew, which is a modern style used in personal handwriting.  In cursive Hebrew, there are mandatory in-word breaks, so that often a single word appears to be two words with a space.

The Arabic alphabet consists of 28 letters, each of which has four forms, depending on whether it is solitary, or initial, medial or final within a word.  Arabic writing also proceeds from right to left.  Today there is only one Arabic script, which is the same for printed texts, like books and periodicals, and for personal handwriting.  Arabic script, whether printed or handwritten, also features breaks, and it is often difficult to see where one word ends and the other begins.  Here is a specimen of modern Arabic.  In bygone centuries, Arabic featured ligatures.  These were elaborate combinations of letters that had to learned independently.

One shortcoming that is shared by Hebrew and Arabic is that there are no letters for vowels.  The letters are strictly consonantal.  In order to read an unvocalized text, i.e., an ordinary text without vowels, one must infer from context which vowels to supply.  This sometimes leads to ambiguities.  In referring to a modern Hebrew newspaper, one can see that there are no diacritic marks below or above the letters, and that means the vowels are absent.  In Bibles, dictionaries and poetry, vowels are supplied.  These consist of dots and bars superadded to the unvocalized text, as here in the first page of Genesis.  In a modern Arabic newspaper, one can see diacritic marks, which, however, are not vowels.  Each diacritic mark, consisting of one, two or three dots, is an inseparable element of the figure on the line that it accompanies.  In the vocalized text, as here in this excerpt from the Qur'an, further diacritic marks, in the form of lines and squiggles but not dots, are added to the essential dots.  These are the vowels.

A modified version of the Arabic alphabet is used also in Persian (Farsi), Urdu, Uyghur, Pashto and other languages.  Formerly, it was used in Turkish and Chagatai (Uzbek), which have now turned to other alphabets.

Both the Hebrew and Arabic alphabets, in their unvocalized forms, are woefully inadequate for the task of representing the sounds of their respective languages, and in both cases, the effort involved in adding the vowels by means of diacritic marks, as in the vocalized specimens presented above, has caused them to remain in disuse.

Another shared disadvantage is that right-handed writers cannot see what they have just written, covering it with their hands as they move right to left.

Arabic is distinguished from Hebrew in that all 28 consonants are non-silent and unique in pronunciation, at least theoretically.  In practice, certain consonants tend to become indistinguishable.  Hebrew has two letters that are entirely silent, and three pairs of letters not distinguished from each other pronunciation-wise.

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