The fact that both writing and verse are organized into hierarchies of constituents is not accidental; it reflects a basic fact about language. If writing evolved, as it did, on a basis of layered constituency, and if poetry displays similar kinds of structure, this is because natural speech is already based on patterns of this kind – they are part of the phonological system of a language; and if such patterns are present in phonology, this in turn is because they are present in the underlying organization of linguistic form – namely in the system of the grammar. A language therefore embodies a multiplicity of constituent hierarchies, coexisting in different parts of the system. They are not unrelated: on the contrary, they are all different facets of the same phenomenon, the fact that experience itself, at least in some of its aspects, imposes a costituent-like structure on our consciousness.
- Halliday (1985), a pag.18

In fact there can be no such thing as a ʻcompleteʼ account of the grammar of a language, because a language is inexhaustible. Although there can only be a finite body of text, written or spoken, in any language, the language itself – the system that lies behind the text – is of indefinite extent so that however many distinctions we introduced into our account, up to whatever degree of fineness or ʻdelicacyʼ, we would always be able to recognize some more.
- Halliday (1985), a pag.XIII

Language has evolved to satisfy human needs; and the way it is organized is functional with respect to these needs – it is not arbitrary.
- Halliday (1985), a pag.XIII

A language, then, is a system for making meanings: a semantic system, with other systems for encoding the meanings it produces.
- Halliday (1985), a pag.XVII

There is no very sharp line between the congruent and the metaphorical – there rarely are any sharp lines in language, since it is an evolved system and not a designed one.
- Halliday (1985), a pag.XIX

The orientation is to language as social rather than as individual phenomenon, and the origin and development of the theory have aligned it with sociological rather than psychological modes of explanation.
- Halliday (1985), a pag.XXX

The classroom image of grammatical structure is something like the following. Language is made up of sentences (some of which have clauses in them) consisting of words (some of which are grouped into phrases).
- Halliday (1985), a pag.25