Writing system

A writing system is a method of representing speech in a more durable medium. Writing systems require shared understanding between writers and readers of the meaning behind the sets of characters that make up a script. A writing system consists of the following:
 * 1) A defined set of elements or symbols, known individually as characters, signs, or graphemes, and known collectively called a script.
 * 2) A set of rules and conventions (orthography) understood and shared by a community, which assigns meaning to the base elements, their ordering, and their relation to each other.
 * 3) At least one language whose that is encoded, such that another reader can reconstruct, with a fair degree of accuracy, the exact utterance written down.
 * 4) Some physical means of distinctly representing the symbols in a permanent or semi-permanent medium.

Writing systems are distinguished from other symbolic communication systems in that a writing system is always associated with at least one language, and one must usually understand something of the associated language to comprehend the text. This is in contrast to to drawings and other non-verbal symbols.

History of writing
Writing systems were preceded by proto-writing, which used pictograms, ideograms and other mnemonic symbols. Proto-writing differs from true writing as it lacks the ability to express a full range of ideas present in language. Proto-writing system are generally difficult or even impossible to understand unless one is already familiar with the information being recorded, as they serve more as visual reminders rather than direct encoding of speech.

The independent invention of writing is rare throughout history. It was long thought that writing was invented in a single civilization (generally in Mesopotamia) and spread over the world from there via a process of cultural diffusion. According to this theory, the concept of representing language with written marks, though not necessarily the specifics of how such a system worked, was passed on by traders or merchants traveling between regions. This theory is known as "monogenesis".

However, scholars now recognize that writing was likely independently developed in at least four ancient civilizations: Mesopotamia (between 3400 and 3100 BCE), Egypt (around 3250 BCE), China (1200 BCE) , and Mesoamerica (by 500 BCE).

Since writing was invented in Mesopotamia and Egypt around the same time, and since they are in the same region it is debated whether the two were independent inventions or a case of cultural diffusion. However, it has been argued that the two writing systems differ so greatly in structure and style they must have developed independently. If there was cultural diffusion, it was simply the concept of representing language with written marks.

Regarding China, it is believed that ancient Chinese characters are an independent invention because there is no evidence of contact between ancient China and the literate civilizations of the Near East, and because of the distinct differences between the Mesopotamian and Chinese approaches to logography and phonetic representation.

Debate surrounds the Indus script of the Bronze Age Indus Valley civilization, the Rongorongo script of Easter Island, and the Vinča symbols dated around 5500 BCE. All are undeciphered, and so it is unknown if they represent true writing, proto-writing, or something else.

Developmental stages
A conventional "proto-writing to true writing" system follows a general series of developmental stages:
 * Picture writing system: Simplified pictures directly represent objects and concepts. The following substages may be distinguished:
 * Mnemonic: Glyphs primarily as a reminder.
 * Pictographic: Glyphs directly represent an object or a concept.
 * Ideographic: Glyphs are abstract symbols that directly represent an idea or concept.
 * Transitional system: Glyphs refer not only to the object or idea but also the name of the object or idea.
 * Phonetic system: Glyphs refer to sounds or spoken symbols, and the form of the glyph is not related to its meanings. This resolves itself into the following substages:
 * Verbal: Grapheme (logogram) represents a whole word.
 * Syllabic: Grapheme represents a syllable.
 * Alphabetic: Grapheme represents an elementary sound.

Classification
Writing systems can be placed into broad categories based on how they represent the sounds of the language. The most common and basic one being a broad division logographic, syllabic, and alphabetic/segmental.

Logographies have a single character to represent a single word or morpheme. Based on the earliest examples of writing logographies always seem to be the first system to develop, with purely syllabic and segmental systems developing out of logographies. In syllabaries each character correlates to a syllable or mora. In alphabets/segmental systems a character can correlate to an individual phoneme.

Difference between writing and language
There are many ways in which written and spoken language differ.

While both writing and speech are useful in conveying messages, writing differs in also being a reliable form of information storage. Writing is permanent or semi-permanent and the same text can be read multiple times. As such a written text can communicate across time and space for as long as the particular language and writing system is understood. Speech is transient, words do not persist after they are said.

Writing is almost never a one to one representation of spoken language. It is rare for writing systems to be completely phonemic (see next section). Additionally the punctuation and layout of written texts have no spoken equivalent.

Phonemic orthography
In an ideal orthography, there would be a one-to-one correspondence between the graphemes and the phonemes of the language. This ideal situation is rare, and if it does exist is often does not last due to sound changes. In less formal terms, this is described as regular and irregular spelling. Another possible term is deep and shallow orthographies, in which the depth of an orthography is the degree to which it diverges from being truly phonemic. Once established, writing systems generally change more slowly than their spoken counterparts. Thus they often preserve features and expressions which are no longer current in the spoken language.

There was several ways in which orthographies may deviate from the ideal of one-to-one grapheme-phoneme correspondence.
 * A phoneme may be represented by a sequence of letters, called a multigraph, rather than by a single letter (for example, the digraph th in English and the trigraph sch in German). Some languages use diacritics to distinguish between a digraph and a sequence of individual letters, and others require knowledge of the language to distinguish them. This usually occurs when a language adopts an alphabet, but the alphabet does not have enough letters to correspond to all the sounds in the language.
 * Different letters or or groups of letters, may correspond to the same phoneme (for instance u and ó in Polish are both pronounced as the phoneme /u/). That is often because of sound mergers. That affects the predictability of spelling from pronunciation but not necessarily vice versa.
 * A letter or group of letters may correspond to different phonemes in different contexts. For example, c in English can be pronounced as /s/ or /k/ (as well as other, rarer pronunciations).
 * Spelling may otherwise represent a historical pronunciation, such as the k in knight no long being pronounced.
 * Spelling may represent the pronunciation of a different dialect from the one being considered.
 * Spellings of loanwords may adhere to or are influenced by the orthography of the source language.
 * Spelling may not reflect phonological assimilation or other changes in pronunciation caused by context.
 * Spelling may reflect morphophonemic structure rather than the purely phonemic. For example, the English plural morpheme is written -s regardless of whether it is pronounced as /s/ or /z/. This is because the [s] and [z] sounds are forms of the same underlying morpheme, automatically pronounced differently depending on its environment.
 * Aspects of the language, such as tone or stress, might not be written despite being phonemic.