How the Alphabet Was Born from Hieroglyphs (2010)
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In fact, most Egyptian hieroglyphs had multiple readings, the same sign standing alternatively for a single sound (letter or syllable), a single word, or some more or less broad concept. Other cultures also had similar systems, or used syllabaries or partial alphabets (abjads [2] and abugidas [3]), or a liberal mix of several systems.
In other words, the idea of alphabetic writing (representing atomic sounds rather than entire words or phrases) did occur more than once. It's only a very small hop from a syllabary to a full alphabet, anyway.
What is unique to the Proto-Sinaitic alphabet discussed in the OP then, is probably the fact that it used the phonetic reading as its sole system, probably for the reasons detailed in the OP: it was used by officially "illiterate" people who didn't have the opportunity to learn (or use!) a more complex script.
So, I guess, their big innovation was not phonetic writing per se, but the fact that they distilled it down to the cheapest, dirtiest, fastest-to-learn bits that could be used by people with very few resources.
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[1] https://en.wikipedia.org/wiki/Transliteration_of_Ancient_Egy...
Devanagari ... also called Nagari is an abugida (alphasyllabary) alphabet of India and Nepal.
The distinction is kind of subtle and like I say in another comment, the idea of using symbols to represent the shortest possible phonemes in a language was not invented by the inventors of the Proto-Sinaitic script. The OP might be exaggerating this point a bit.I'm also not totally convinced that learning a complex writing system like an ideographic script is such a big deal. After all, if all you want is a way to write down your name or a short prayer (longer prayers would be prohibitive by having to carve them on stone during either work, or breaks from work, anyway) you can always do that with ideograms. You can always learn only the few symbols that say what you want to say; you don't have to learn the entire script!
Come to that, there's no real way to tell whether the people who wrote their names in the Proto-Sinaitic script actually knew how to read the entire alphabet, short as it was. Maybe they only knew the characters for their name, and then a handful of other characters outside it, perhaps the ones used in the names of popular deities or their friends etc.
I mean, sure, that proto-alphabet had an easy mnemonic, but that doesn't mean that everyone who knew how to write their name in it had actually made the (small, but not nonexistent) effort to commit the entire thing to memory. It probably takes kids today a good few months to learn to read and write using an alphabet even with all the leisure and support of modern education systems. I can't see the miners of Serabit having an easier time at it.
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Of course there's the the Indus Valley script, but theres no real evidence to suggest that it was used to write significant and lengthy works. Especially since the IVC collapse would have predated the migration of the Aryans. But there actually doesn't need to be a common writing system, since we know for a fact it originated independently in two places, the Sumerians and the Maya. It's less clear cut (no ocean separating) but it's likely the Oracle Bone script in China was independent too.
If you want to see the original script, look at a Samaritan Pentateuch.
https://en.wikipedia.org/wiki/Cherokee_syllabary
(Although that someone who invents an alphabet can be considered to be illiterate is interesting)
I also wonder how many of the people who adapted the Chinese hanzi to their local languages were actually literate in Chinese.
The Rosetta mission as told in emojis
The lack of written vowels would also held simplify learning.