Register Vs Text Type

'Register' and 'text type' occupy the same point on the cline of instantiation.
Looking from the system pole, it is 'register'.
Looking from the instance pole, it is 'text type'.

Why an instance is 'a token of a type'

The organising principle of the cline of instantiation is attribution (Halliday & Matthiessen 1999: 14-5, 145).

Attribution is concerned with class membership.
Attribution + elaboration includes type–subtype relations.

But, the most delicate subtype has just a single member.
The relation between a category and its single member is identification.
The category and the member uniquely identify each other.
The member is the Token that realises the category Value.
An instance is the Token that realises the most delicate category Value.

This is the distinction between instance and subtype.

Realisation

Choices at higher strata do not determine choices at lower strata.
Function does not determine form.
Paradigm does not determine syntagm.

Choices at higher strata do not precede choices at lower strata.

Function does not precede form.

Paradigm does not precede syntagm.

Strata are different levels of symbolic abstraction.

Function and form are different levels of symbolic abstraction.

Paradigm and syntagm are different levels of symbolic abstraction.

The relation between these different levels of symbolic abstraction is 'intensive identifying', not 'circumstantial identifying' (ie neither 'causal' nor 'temporal').

Types Of Theoretical Misunderstanding

Misunderstandings of SFL theory include the following two types:

(1) Misunderstanding the terminology of the theory

(2) Misunderstanding the architecture of language proposed by the theory

A complex variant of the second type is the practice of blending two distinct dimensions while purporting to be concerned with only one of them.