We take writing and language for granted, but there's remarkable history and variability in how it's all constructed across time and space with humanity, and even large variation today — not just in language, but in how we convey it in writing.
This is a great family tree of alphabets — and isn't very conjectural at all, since we actually know how writing spread. The color codes are by kinds of writing.
The oldest forms of writing are true pictograms, not shown here; these are scripts like the earliest forms of Egyptian, Sumerian, and Chinese writing, which are basically pictures (slightly stylized) of physical objects. These aren't full writing systems, in that they can generally only code things like "three sheep, four barrels of wine…"
These quickly evolved into logograms, a few of which are shown here in blue — not only the bulk of ancient Egyptian, but also modern Chinese and part of modern Japanese writing as well. In logograms, a small group of symbols represents a word, not phonetically but conceptually. (This is why the different Chinese languages, which sound almost nothing alike, can nonetheless share a single writing system! The writing codes ideas, not sounds.)
A common extension of logograms is to add sound representations, typically starting with using words to represent homonyms, and then adding logographic marks to indicate "the word symbolized by <X> which sounds like <Y>" to clarify synonyms, and so on. Nearly all logographic writing systems adopted this.
Ancient Egyptian did in particular, and an entire subbranch of its writing system started to adopt this more seriously, starting to use purely phonetic representations — that is, symbols that described sounds instead of concepts. This is one of the earliest forms of alphabetic writing.
This kind of "phonetic writing" then has a history which you can see here.
Abjads are scripts like Hebrew and Arabic, where each letter represents a syllable, but only uniquely describes the consonants; you're supposed to know the vowels from context. These work well in languages where the vowels vary following predictable rules and primarily indicate parts of speech, and so are still used in such languages to this day. (The name "abjad" comes from the first four letters of the old Arabic alphabet, a, b, j, and d.)
Abugidas (green) and alphabets (red) take this further, adding accent marks (in abugidas) or separate letter-signs (alphabets) for the vowels, as well. As Barry Powell argued in Homer and the Origins of the Greek Alphabet, this likely emerged as a pattern whenever abjads reached areas where the local language didn't have the same kinds of rules for vowels as Semitic languages, and the ability to explicitly code vowels was important for telling words apart — and, critically, for recording poetry and verse.
Finally, featural alphabets take the march towards phonetic clarity even further. The classic example of this is Hangul, the script invented for Korean in the 15th century. In these writing systems, symbols go beyond coding for sounds — they code for individual features, like "plosive sounds" (you stop the air and then suddenly release it, like t or p), "aspirated sounds" (with a breath), and so on. So for example, ㅌ can be immediately recognized as a voiceless, aspirated, alveolar plosive, or tʰ.
English is in many ways a strange case in this family. The Latin alphabet that it uses is a true alphabet: someone reading Latin immediately knows how to pronounce any word they see, just like someone reading Spanish or Polish would. But English both assembled its lexicon from a bunch of languages, and standardized its spelling system much earlier than most other modern languages — and unfortunately, did so not too long before a major change in how words were pronounced, which gives it all sorts of oddities like "silent e," how tough it is to cough through a rough slough, and so on. (There are not many languages where "being able to spell things correctly" is a televised sport!) In fact, despite its use of an alphabet, English is in many ways moving back towards being a logographic language, where you have to know what a word is (and which language it comes from) to know how to pronounce it.
Via +John Hardy
