Over the past week, I have been hard at work on a couple of rather involved music-analytical posts, as well as various of the Mathematics Lectures. It occurred to me, however, that I might take a bit of time out to begin the promised systematic exposition of Westergaardian theory. For one thing, it would be nice to have something online to refer to when writing up analyses; but, to be honest, the proximate reason I decided to start this now was that there are some things I would really like to get off my proverbial chest, and the appropriate place to do so will be in the second post of this series, which will be about the concept of lines.
First, we have to talk about notes. This material comes from chapter 2 of ITT, though my discussion of pitch differs in some minor respects from Westergaard’s. (For the moment, I’m skipping chapter 1, which deals with meta-issues, because 1) I’m in a hurry to get to chapter 3 and 2) there will be plenty of opportunity to talk about meta-issues as they come up.)
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The most basic element of musical structure is the note. A note is defined to be a unit of sound that we think of as having
- a particular pitch
- a particular onset time
- a particular duration
In addition, we may also think of a note as having
- a particular loudness
- a particular timbre
The first three attributes are mandatory: they are necessary to determine the syntactic value of a particular note. By contrast, the latter two attributes are in a sense optional: their function is to clarify or reinforce the syntactic value of a note.
I assume that readers are familiar with musical fundamentals, and so I won’t bother to go into too much detail here about how each of these dimensions is conceived; a quick run-through will have to suffice. If anything needs clarification, feel free to ask in the comments. Note that Westergaard gives a characteristically thorough exposition in chapter 2 of ITT. That exposition is far superior to the one given here, as will be obvious to anyone who reads both.
Pitch
The space of pitches is divided into semitones. A semitone is the interval from the pitch of one key on a piano to the pitch of an immediately adjacent key. The size of a semitone is such that the interval of twelve semitones corresponds to a doubling of the frequency (recall that pitch perception is logarithmic with respect to frequency, so that pitch intervals correspond to frequency ratios). Such an interval is called an octave. For some purposes we shall consider pitches an octave apart to be equivalent; the equivalence classes so obtained are called pitch-classes. We name pitch-classes by numbers 0,1,2,…10,11 (0 being the class of the pitch of the “middle C” key on a piano, 1 being the class of the next higher key, and so on), or by letters in a manner that will be discussed below (“middle C” being indeed an instance of this nomenclature).
We conceive of pitches not only as elements of the semitonally-divided pitch space, but also as elements of special subsets of this space called “diatonic collections”. Consider the pitches of the seven white keys on a piano starting from middle C and continuing upward (to the right); call this collection of pitches S. We define a diatonic collection to be a transposition of S by some number of semitones. (Thus S itself is an example of a diatonic collection.) By abuse of language, we also use the term “diatonic collection” to refer to the set of pitch-classes corresponding to the pitches of some diatonic collection.
This furnishes an alternative nomenclature for pitch-classes, defined as follows. For historical reasons, the pitch-class 9 is called A. The elements of the diatonic collection {9,11,0,2,4,5,7} are then called respectively A,B,C,D,E,F,G. Arbitrary pitch-classes, in turn, are named as if they were conceived of as transpositions of an element of this collection. Thus pitch-class 1 may be called
(upward transposition of C by one semitone),
(downward transposition of D by one semitone),
(conventionally written
; upward transposition of B by two semitones),
(downward transposition of E by three semitones; or indeed
, downward transposition of
by two semitones), etc. This system is convenient because we do indeed conceive of pitches in terms of some diatonic collection (though the particular collection is determined by context, and is not always {A,B,C,D,E,F,G}).
We also use diatonic collections (in the strict sense, as a collection of pitches, rather than pitch classes) to conceive of intervals between pitches. The interval from a pitch to itself (such as from middle C to middle C) is called a unison (or prime). An interval between adjacent members of a diatonic collection is called a second (or step). Other intervals are named according to the number of seconds from which they are built up:
Two seconds: third
Three seconds: fourth
etc.
A second may be either a semitone (half-step, or minor second) or 2 semitones (whole-step, or major second). Likewise, other intervals come in different varieties, depending on how many of the seconds used to construct them are major and how many are major. (Any pattern may be used provided that it fits into a diatonic collection; thus a third may be built out of two major seconds, or out of a major second and a minor second, but not two minor seconds.) The intervals of a unison, an octave (seven diatonic steps), a fourth of the type consisting of two major seconds and a minor second (as from a particular member of pitch-class C to the first member of F above), and a fifth of the type consisting of three major seconds and a minor second (as from C to G) are called perfect intervals. An interval obtained from a perfect interval by raising the higher pitch (or lowering the lower pitch) by a semitone is said to be augmented; thus the interval from a (particular member of the pitch-class) C to the first (member of) F# above is an augmented fourth. Likewise, an interval obtained from a perfect interval by lowering the higher pitch (or raising the lower pitch) is said to be diminished: thus the interval from C to Gb is a diminished fifth.
(Note that Gb and F# both refer to pitch-class 6, so that both an augmented fourth and a diminished fifth refer to an interval of six semitones; such pairs of pitches or intervals are said to be enharmonically equivalent.)
Other intervals (thirds, sixths, and sevenths) come in two types, as the reader can easily verify. The larger type of each is called major, and the smaller type minor. Expanding a major interval by a semitone yields (again) an augmented interval; contracting a minor interval by a semitone likewise yields a diminished interval. (Thus C to A# is an augmented sixth; C to Ebb is a diminished third.)
Time
From ITT, sec. 2.2:
We conceive of time in tonal music in terms of systems of equally spaced reference points…We call the reference points beats. If a note begins at a reference point we say it is “on the beat”; if note, we say it is before or after the beat or simply “off the beat”. We call primary reference points downbeats. Secondary reference points are sometimes called upbeats, but properly speaking upbeat is reserved for that secondary reference point immediately preceding the next downbeat. We call the span between consecutive primary reference points a measure. We say that a note that begins on the downbeat and lasts until the next downbeat “lasts a measure”. We call the segments formed by the secondary reference points beats*.
If a note begins on one beat and lasts to the next beat we say it “lasts a beat”. We call the way the secondary reference points divide the spans between primary reference points the meter. One secondary beat dividing each measure into two equal parts is called duple meter; two secondary beats dividing each meaure into three equal parts is called triple meter. We call the rate at which beats occur the tempo. A rate of around 85 beats per minute (time from one beat to the next is about
seconds) is usually considered a moderate tempo; most tempos fall between twice and half that rate.
*An unfortunate double use of the same term to mean both a point in time and a period of time between two points.
Loudness
We conceive of loudness as measured by a scale whose only structure is that of a totally ordered set:

(For further discussion, see ITT, sec. 2.3.)
Timbre
Piano, violin, clarinet, etc.; see ITT, sec. 2.4.