In systemic functional grammar (SFG), a nominal group is a group of words that represents or describes an entity, for example The nice old English police inspector who was sitting at the table with Mr Morse. Grammatically, the wording "The nice old English police inspector who was sitting at the table with Mr Morse" can be understood as a nominal group (a description of someone), which functions as the subject of the information exchange and as the person being identified as "Mr Morse".
A nominal group is widely regarded as synonymous with noun phrase in other grammatical models. However, there are two major differences between the functional notion of a nominal group and the formal notion of a noun phrase that must be taken into account. Firstly, the coiner of the term, Halliday, and some of his followers draw a theoretical distinction between the terms group and phrase. Halliday argues that "A phrase is different from a group in that, whereas a group is an expansion of a word, a phrase is a contraction of a clause". Halliday borrowed the term group from the linguist/classicist Sydney Allen. In the second place, the functional notion of nominal group differs from the formal notion of noun phrase because the first is anchored on the thing being described whereas the second is anchored on word classes. For that reason, one can analyse the nominal groups some friends and a couple of friends very similarly in terms of function: a thing/entity quantified in an imprecise fashion; whereas one must recognise some friends as being a simple noun phrase and a couple of friends as being a noun phrase embedded in another noun phrase (one noun phrase per noun). In short, these notions are different even if formalists do not perceive them as different.
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