The options in a natural language are at various levels: phonological, grammatical (including lexical, which is simply the more specific part within the grammatical) and semantic. Here, where we are concerned with the meaning potential, the options are in the first instance semantic options. These are interpreted as the coding of options in behaviour, so that the semantics is in this sense a behavioural semantics.
- Halliday (1973), a pag.55

Semantics [...] is ʻwhat the speaker can meanʼ. It is the strategy that is available for entering the language system. It is one form of, or rather one form of the realization of, behaviour potential; ʻcan meanʼ is one form of ʻcan doʼ. The behaviour potential may be realized not only by language but also by other means. Behavioural strategies are outside language but may be actualized through the medium of the language system.
- Halliday (1973), a pag.72

There are also sets of options at the two interfaces, the coding levels which relate language to non-language. We use ʻsemanticsʼ to refer to one of these interfaces, that which represents the coding of the ʻinputʼ to the linguistic system. The range of options at the semantic level is the potentiality for encoding in language that which is not language.
- Halliday (1973), a pag.72

Semantics is what he [the speaker] CAN MEAN; and we are looking at this as the realization of what he DOES. But it is ʻrealizationʼ in a somewhat different sense, because what he CAN DO lies outside language [...].
- Halliday (1973), a pag.82