These two functions, the ideational and the interpersonal, may seem sufficiently all-embracing; and in the context of an instrumental approach to language they are. But there is a third function which is in turn instrumental to these two, whereby language is as it were enabled to meet the demands that are made on it; I shall call this the TEXTUAL function, since it is concerned with the creation of text. It is a function internal to language, and for this reason is not usually taken into account where the objects of investigation are extrinsic; but it came to be specifically associated with the term ʻfunctionalʼ in the work of the Prague scholars who developed Bühler’s idea within the framework of a linguistic theory (cf. their terms ʻfunctional syntaxʼ, ʻfunctional sentence perspectiveʼ). It is through this function that language makes links with itself and with the situation; and discourse becomes possible, because the speaker or writer can produce a text and the listener or reader can recognize one. A TEXT is an operational unit of language, as a sentence is a syntactic unit; it may be spoken or written, long or short; and it includes as a special instance a literary text, whether haiku or Homeric epic. It is the text and not some super-sentence that is the relevant unit for stylistic studies; this is a functional-semantic concept and is not definable by size. And therefore the ʻtextualʼ function is not limited to the establishment of relations between sentences; it is concerned just as much with the internal organization of the sentence, with its meaning as a message both in itself and in relation to the context.
- Halliday (1973), a pag.107

There is also a third macro-function, the ʻtextualʼ, which fills the requirement that language should be operationally relevant – that it should have a texture, in real contexts of situation, that distinghuishes a living message from a mere entry in a grammar or a dictionary. This third component provides the remaining strands of meaning potential to be woven into the fabric of linguistic structure.
- Halliday (1973), a pag.42