The mood system belongs to the interpersonal metafunction of language. Here, we are interested in the clause as exchange; specifically, we are interested in the grammatical resource that realises different interactional moves in a discourse.
Although there may be some connection, Halliday's mood system has very little to do with your emotional state right now, normal or otherwise.
Right from the start, it would be a good idea to separate the traditional notion of mood from the technical sense in which Halliday uses it. Traditionally, mood refers to the verb forms that express a fact or action (a.k.a. indicative = declarative, interrogative), command (imperative), or doubt (subjunctive). Note, though, that subjunctives are not discussed in the Hallidayan framework.
In the Hallidayan framework, mood, unless otherwise specified, refers technically to the mood block, which comprises the following components:
[To disambiguate the terms, we shall use "clausal mood" to refer to the traditional notion of mood (declarative, interrogative, etc.), and "mood" to refer simply to how it is used in the Hallidayan framework.]
Moving on. The S, F, and modal adjuncts all come under the mood block. All other elements come under residue, except the following which are to be omitted from your analysis:
You may wonder, quite rightly, why vocatives and expletives are to be omitted since they are clearly interpersonal in function. Well, the answer is that they are peripheral [incidental, if you like] to the act of giving and receiving of information or goods/services. So for mood analysis, you can leave them out.
So far so good? Now the next big thing you need to do is to chop up the clause into the mood and residue blocks. Before that, however, please refresh your memory about SVOCA that you learned in your first-year grammar course (when dinosaurs once roamed the earth).
... refreshing, refreshing, refreshing, ...
Done? Okay ... you'll now need to make some slight adjustments, as follows:
What's the difference between complement and adjunct? Halliday & Matthiessen (2004: 122-124) say:
"A complement is an element within the Residue that has the potential of being Subject but is not ... It is typically realized by a nominal group."
"An Adjunct is an element that has not got the potential of being Subject ... An Adjunct is typically realized by an adverbial group or a prepositional phrase (rather than by a nominal group)."
So that's quite clear, isn't it? Now comes the easy bit. When you analyse the clause using Halliday's SFPCA, it becomes a breeze to locate the mood block -- group the S and F under MOOD, and the P and C under RESIDUE.
What about adjuncts then? Aha ... you need to be a little careful here. There are two types of adjuncts you need to worry about -- modal adjuncts and the residue adjuncts. For ease of reference, let's refer to the latter as ARs (short for "residue adjuncts"). ARs provide circumstantial information (things to do with time, place, manner, etc.), including the by agents of passive clauses, such as "the cake was eaten by him". All ARs form part of the residue.
Modal adjuncts (let's call them AM), on the other hand, form part of the mood block. They provide additional information on likelihood, usuality, etc. (mood adjuncts), or the speaker's opinion, comment, etc. (comment adjuncts). Please note that AMs include both mood and comment adjuncts.
To give you a feel of what is involved in mood and comment adjuncts, have a look at the table below. Please note that the table is merely for your reference; you do not need to memorise the wretched thing. From the table, hopefully, you should get a sense of what an AM is, and how you can identify it:
Here are a few examples of mood and comment adjuncts:
In summary, then:
You might have guessed by now that S and F are pretty important components of the mood block. What's so special about them? Let's begin with the F element.
What the F element does is that it enables something to be argued about. Halliday & Matthiessen (2004: 115) note that "a good way to make something arguable is to give it a point of reference in the here and now; and this is what the Finite does." Something may be made arguable by being presented in terms of time (John belched; past time), modality (John might have belched; probability), or polarity (John did belch; positive polarity). (See below for the modality in finite verbs.)
The S element, on the other hand, enables a proposition to be affirmed or denied. The subject is that element that is responsible for the functioning of the clause as an interactive event.
The sequential arrangement of S and F also realises different clausal moods. The typical patterns are as follows:
1. Marrying and divorcing F and P
In a finite clause, if the VG consists of only one verb, F is conflated with P -- you therefore label the verb as F/P. (Of course, if the clause is NF, there is no F element to worry about.) Hence:
The easiest way to pick out the F element is to insert a mood tag, which picks out the F and S elements of the main clause. In (1), the mood tag -- didn't it -- raises a puzzle since the main clause doesn't contain the verb did. Eggins (1994: 158) clarifies: "Where does the did in the tag come from? What happens is that with verbs in the simple present or simple past declarative, the Finite element gets fused with another element, known as Predicator. In earlier forms of English, and still in emphatic forms of contemporary English, the did used to be present in the main part of the clause as well as in the tag [...] I did learn the English language from the guy, didn't I? [...] In unemphatic modern English, the did Finite has become fused in with the content part of the verb. But technically it is still there in the clause, as we see when we add the tag."
Moving on, if the VG in a finite clause consists of more than one verb, it is always the first verb that gets labelled F. Everything else in the VG is P:
What about multi-word verbs (such as phrasal or prepositional verbs)? Mainstream systemicists would treat them as comprising a fused element of finite/predicator followed by an adjunct -- for example, switch (F/P) on (A). I feel, however, that it would be a lot neater to simply regard the particles in such multi-word verbs as an extension of the verb and, therefore, part of the predicator. Hence:
Finite verbs are verbs that are marked for tense and/or modality. Modality here refers to degrees of indeterminacy. It does not refer only to modal verbs such as "can/could", "may/might", "shall/should", "will/would", "must", or marginal modals such as "used to", "had to", etc. Indeed, the notion of modality can be extended to any lexical verb, not just modal verbs.
In the case of verbs, modality is manifested in two ways:
Do note that the labels above are for verbs only, not for AMs. (The AM labels are more complex -- as you must have realised by now unless you scrolled down this page too quickly.)
When analysing verbs, it might be helpful to consider how they are used from this modality angle (... "might" here is an example of modalisation:probability). At an introductory level, you should perhaps keep it simple by restricting your choices to just modalisation (probability, usuality) and modulation (obligation, inclination).
Do we need to analyse every single finite verb for modality? Well, nope. You should think of modality only in terms of modalisation and modulation. There is no modality, for instance, in the finite verbs below -- at least, the pea in my head can't detect any:
3. Schizophrenic S
In English, there are constructions where the anticipatory it is used. In such constructions (a.k.a. extraposed-subject constructions), the content of the anticipatory subject is placed at the end:
What happens in such a situation is that S is regarded as being discontinuous, as in:
Which now leads me to the next point.
4. Must the mood block always be a single block?
No -- a clause like "Newton kicked the durian, unfortunately" should give you some idea of the discontinuity that the mood block tolerates.
5. Is the imperative always moodless?
The answer is no. The exclusive imperative is typically moodless, but this need not be the case for all imperatives. The following imperatives, for example, have a mood block:
Eggins, S. (1994). An Introduction to Systemic Functional Linguistics. London: Pinter.