Source: ETCSL
Cuneiform writing was most probably invented in Uruk in southern Mesopotamia (modern Iraq) about 3400 - 3300 BCE (Glassner 2003:45). It was invented to keep records of goods and services, and the language that was recorded was, as far as we can tell, Sumerian. The cuneiform script was later adopted by other people speaking languages as different as Akkadian, a Semitic language, and Hittite, an Indo-European language. Sumerian itself is, as far as we know, not related to any other living language. It is a language isolate.
In its early stages, cuneiform writing was bascially logographic in nature, and a sign represented a content word (a thing or an action). The drawback of a purely logographic writing system is of course that the number of signs needed to represent all the words of a language will run into the thousands. Cuneiform, thus, gradually developed into a combined system, where the same set of signs could be used to represent logograms and phonograms or syllabograms. In texts of our period, i.e. late third and early second millennium, logograms were used to write content words and the base (root) of a word, while phonograms were used to write bound morphemes and loan words.
Language has two basic functions or metafunctions. One is to make sense of our experience, e.g. by listing things or professions that belong together (the experiental metafunction); the other is to act out social relationships, e.g. by asking questions, giving orders, making offers, expressing our attitudes, etc. (the interpersonal metafunction). Both types of functions are normally present in any stretch of language use. However, early cuneiform writing did not usually indicate the second type of function in the writing. This is why we cannot always tell whether someone named in a text is receiving or giving something, recording or accepting something. Thousand years on from the earliest attestations of cuneiform writing, when some of the texts of the ETCSL were written down, the so-called interpersonal metafunction of language was present in the writing system in the form of a more fixed word order, grammatical (bound) morphemes indicating subject, object, modality, aspect, etc., and function words, e.g. pronouns and determiners.
