Why is the alphabet arranged the way it is?
This is an intriguing but unanswerable question. The ancestor of our alphabet is the Phoenician alphabet of nineteen characters (representing only consonants), dating from about the 14th century BC. Around 1000 BC this was used as a model by the Greeks, who added characters to represent vowels. This in turn became the model for the Etruscan alphabet, from which the ancient Roman alphabet, and subsequently all Western alphabets, are derived. Characters have been added over the centuries and others lost, according to the need to represent certain sounds. But the basic order has remained the same. Indeed, it may go back to North Semitic, the ancestor of Phoenician, which developed about 1700 BC. In other words, we do it like this because we’ve always done it like this, but why we did it in the first place, no one knows.
Although the order of alphabetical characters has been established for so long, putting words into alphabetical order has been perfected relatively recently. In medieval times this usually consisted of simply putting together all the words beginning with a, followed by all those with b, and so on. Strict alphabetical order did not become established until after the advent of printing.
Words can be alphabetized in two ways, known respectively as word-by-word and letter-by-letter. In the former, a shorter word will precede all other words beginning with the same sequence of letters, even if the word is followed by another word. In letter-by-letter alphabetization, with characters are considered as a single sequence, with any hyphens and spaces ignored.
Source:From Questions of English, compiled and edited by Jeremy Marshall and Fred McDonald (Oxford University Press, 1996):