There are three undisputed independent developments of writing: Sumerian, Mayan, and Chinese. Egyptian may or may not have been influenced by Sumerian; Indus Va

There are three undisputed independent developments of writing: Sumerian, Mayan, and Chinese. Egyptian may or may not have been influenced by Sumerian; Indus Valley Script may or may not be writing; and Andean quipus (essentially knotted strings) raises interesting questions about what writing even is. All other (known) writing systems developed out of knowledge of these priors. The development of writing systems seems to be pretty clear, especially because we can use Sequoyah's documented development of Cherokee script as a check. Writing seems to start as logographic: each character starts out as representing a word, often as a stylized representation of that word (for example, draw an eye to represent the word 'eye'). To represent words that don't have easy representation, a rebus system develops: you use homophonic puns (so an eye might also stand for 'I'). This lends itself to a simplification to a syllabic representation, one word for each possible syllable. And usually, it stops there (although note that 'syllable' usually comes out in writing as a consonant-vowel pair, rather than a full syllable). It's with the Semitic languages that things took an interesting turn. Semitic languages have an interesting feature in that you can get most of the sense of a word even if you drop the vowels. And the writing ended up switching from consonant-vowel pairs to just consonants (what we now call an 'abjad'). Greek opted to adapt this by adding letters for vowels and formed the first 'true alphabet'. Sanskrit opted instead to use reliable markings on consonants to make an 'abugida'. Chinese never developed their logographic system into a syllabary, although this was probably partially driven by the fact that Chinese itself had most of its words become monosyllabic at the same time. Japanese did continue Chinese script into two full syllabaries. Korean is the other independent invention of an alphabet: Hangul. Although Hangul is arranged as a succession of blocks representing full syllables, so it can also be viewed as a systemic construction of a syllabary rather than an alphabet. I mentioned Sequoyah's development of Cherokee script: he knew of writing from the Americans at the time, and even had access to a Bible (although he couldn't read it at all). And his own documentation of his development does expressly indicate that he started trying to build a logography, realized that there were too many symbols that had to be created, and instead simplified it into a syllabary, which was much more conservative in its character count. (And the influence of several character shapes came from that Bible, which is why Cherokee script looks like someone started with Latin script but had no idea had it worked--here is its character set: ᎠᎡᎢᎣᎤᎥᎦᎧᎨᎩᎪᎫᎬᎭᎮᎯᎰᎱᎲᎳᎴᎵᎶᎷᎸᎹᎺᎻᎼᎽᎾᎿᏀᏁᏂᏃᏄᏅᏆᏇᏈᏉᏊᏋᏌᏍᏎᏏᏐᏑᏒᏓᏔᏕᏖᏗᏘᏙᏚᏛᏜᏝᏞᏟᏠᏡᏢᏣᏤᏥᏦᏧᏨᏩᏪᏫᏬᏭᏮᏯᏰᏱᏲᏳᏴᏵᏸᏹᏺᏻᏼᏽ)