Ergative As Nuclear

Halliday (1994: 167):

Nucleus

Halliday (1994: 164):

Process

Halliday & Matthiessen (1999: 213):

Thus from the point of view of the figure, a process is the central element, forming a nucleus around which participants and circumstantial elements are organised into a meaningful pattern. 

From the point of view of its own internal organisation, a process is the construal of 'eventing' — a phenomenon perceived as having extension in time.

The Process As The Central Element Of A Figure

Halliday & Matthiessen (1999: 213):

The key to the construal of experience is the perception of change; the grammar construes a quantum of change as a figure (typically one clause) and sorts out figures in the first instance into those of consciousness (sensing and saying), those of the material world (doing & happening) and those of logical relations (being & having). The central element of a figure is the process; 'things' are construed as entities participating in processes, having different roles, of which one is 'that participant in which the process is actualised' (if there is 'flying', there has to be something that flies or is flown: birds fly, people fly kites); hence the grammatical nucleus of the clause is the configuration of Process with Medium.

The Nucleus Of A Figure

Halliday & Matthiessen (1999: 156):

Semantically, the nucleus construes the centre of gravity of a figure, the focal point around which the system of figures is organised. When we describe the Medium as "actualising" the Process, we are really saying that the unfolding is constituted by the fusion of the two together — there can be no Process without an element through which this process is translated from the virtual to the actual.

Manifestations Of The Close Bonding Of Medium And Process As Nucleus [3]

Halliday & Matthiessen (1999: 156):

The manner of performance of a process may vary, in which case it is the Medium by which it is typically determined. This may be a major variation in the mode of actualisation, for example 'open + door, open + account, open + eye' where the process is respectively mechanical, verbal or physiological; or simply a minor difference in the means that is employed, e.g. "brush + teeth, brush + clothes'. Some examples:

In many cases, the difference in the manner of performance is the basis of a lexically codified taxonomic distinction; for example:

Manifestations Of The Close Bonding Of Medium And Process As Nucleus [2]

Halliday & Matthiessen (1999: 155):

In the taxonomy of figures, the nature of the Medium is more criterial than that of any other participant or circumstance. For instance, if we consider processes such as 'strew, spill, pour, sprinkle', it is the Medium, not the Agent which enables us to differentiate among them (cf. sprinkle + salt, spill/ pour + water, coffee; strew + flowers); similarly with 'bend, straighten, flatten; melt, freeze, evaporate, condense; crack, break, shatter' and so on.

Manifestations Of The Close Bonding Of Medium And Process As Nucleus [1]

Halliday & Matthiessen (1999: 155):

Of all the participants, the Medium is the most restricted in terms of the range of phenomena that may function in that role. We can see this in relation to the general types of figure:

We can also see this in relation to more delicately specified subtypes such as:

In other words, whatever the type of figure, the participant that is most closely bonded with the Process is the one that takes on the generalised role of Medium; it is this that is in a relation of mutual expectancy with the Process. This is not to say that only horses can neigh, but rather than anything that neighs is thereby endowed with horse-hood.

Blogger Comments:

Clearly, the Medium of a 'shine' figure is not limited to 'heavenly body', but includes artificial light sources and phenomena with reflective surfaces, such as black shoes.

Generalised Model of Figures: Nucleus

Halliday & Matthiessen (1999: 154, 134):

Medium and Process form the nucleus of the whole figure — that part of the figure which is essential to the complementarity of unfolding and persisting (cf. Figure 4-3 above). The participant functioning as Medium may be affected in various different ways, depending on the particular domain — the 'trace' may b[e] physical, mental, and so on; but the status of Medium generalises across these domains.

Agent: External Cause

Halliday & Matthiessen (2014: 336):

The difference between ‘doing’ and ‘happening’ derives from a different principle from the transitive one of extension–and­–impact: ‘happening’ means that the actualisation of the process is represented as being self–engendered, whereas 'doing' means that the actualisation of the process is represented as being caused by a participant that is external to the combination of Process + Medium [i.e. Nucleus]. This external cause is the Agent.

Circumstances: Logico-Semantic Relations To The Nucleus

Halliday & Matthiessen (1999: 173):

… cutting across this cline of involvement, we find that — like the participants themselves — the circumstantial elements fall into distinct types according to their relationship to the Process + Medium nucleus. These types correspond to the four transphenomenal categories of the logico-semantic relations that are now familiar: the circumstance is either a circumstance of projection or a circumstance of expansion and, if the latter, then either elaborating, extending or enhancing.

The Nucleus

Halliday & Matthiessen (1999: 156):

Semantically, the nucleus construes the centre of gravity of a figure, the focal point around which the system of figures is organised. When we describe the Medium as “actualising” the Process, we are really saying that the unfolding is constituted by the fusion of the two together — there can be no Process without an element through which this process is translated from the virtual to the actual.

The Close Bonding Of Medium And Process: Medium And Manner Of Performance

Halliday & Matthiessen (1999: 156):

The manner of performance of a process may vary, in which case it is the Medium by which it is typically determined. This may be a major variation in the mode of actualisation, for example ‘open + door, open + account, open + eye’ where the process is respectively mechanical, verbal, or physiological; or simply a minor difference in the means that is employed, e.g. ‘brush + teeth, brush + clothes’. In many cases, the difference in the manner of performance is the basis of a lexically codified taxonomic distinction.

The Close Bonding Of Medium And Process: Medium As Criterial Of Figure Type

Halliday & Matthiessen (1999: 155):

In the taxonomy of figures, the nature of the Medium is more criterial than that of any other participant or circumstance. For instance, if we consider processes such as ‘strew, spill, pour, sprinkle’, it is the Medium, not the Agent, which enables us to differentiate among them (cf. sprinkle + salt, spill/pour + water, coffee; strew + flowers); similarly with ‘bend, straighten, flatten; melt, freeze, evaporate, condense; crack, break, shatter’ and so on.

The Close Bonding Of Medium And Process: Restrictions On Medium

Halliday & Matthiessen (1999: 155):

Of all the participants, the Medium is the most restricted in terms of the range of phenomena that may function in that rôle. We can see this in relation to the general types of figure: 

type of figure	range of phenomena functioning as Medium
doing	phenomenon (of any kind — but not a metaphenomenon, i.e. not fact)
sensing	conscious being
saying	symbol source
being	phenomenon (of any kind, including metaphenomenon)

[…] In other words, whatever the type of figure, the participant that is most closely bonded with the Process is the one that takes on the generalised rôle of Medium; it is this that is in a relation of mutual expectancy with the Process.

The Generalised Model Of Participation-In-Process: The Nucleus

Halliday & Matthiessen (1999: 154, 155):

Medium and Process form the nucleus of the whole figure — that part of the figure which is essential to the complementarity of unfolding and persisting. […] The model thus construes a nuclear figure consisting of a process unfolding through the medium of a participant. […] It is in the combination of Medium + Process that we find the complementarity between the temporal unfolding (the Process) and the atemporal persistence (the Medium).