Pc is the abbreviation for pitch-class. A pitch-class is the set of all enharmonically equivalent notes related by any number of octaves. All C♯s and D♭s form a single pitch-class; all C♮s, B♯s, D♭s form another pc. There are twelve pitch-classes, known informally as “twelve-tones” or the “notes of the chromatic scale.” I often use the term “note” to mean pitch-class in much of this book. Numbers are often used to denote the twelve pcs. 0 = C, 1 = C♯/D♭, 2 = D, 3 = D♯/E♭, 4 = E, 5 = F, 6 = F♯/G♭, 7 = G, 8 = G♯/A♭, 9 = A, 10 = A♯/B♭, and 11 = B. I use the letters A for 10, and B for 11, so A = 10 = A♯/B♭ and B = 11 = B♮.

A row is an ordering of pcs without duplication. This is much more elegant and precise than saying something like “a row is the notes of the chromatic scale placed in any order without repetition, and a row can be played with its notes in any octave register.” I don’t use the (Princetonian) term “set” for row. A set is an unordered collection of elements; a row is ordered.

The aggregate is the set of all twelve tones in any ordering. A row is an aggregate; a twelve-tone cluster is an aggregate; the combination or succession of a C-major chord, a D-minor chord, a G#-minor chord, and a F#-major chord is an aggregate; and so on.

A set of transformations can be the familiar, classical row operations of transposition, inversion, and retrograde, which in all combinations produce 48 different transformations, but there are other transformations as well.

Row-classes are sets of rows related by a set of transformations. Given a row we call P, the classical transformations of P include P, its inversion (IP), its retrograde (RP), and its retrograde inversion (RIP), along with all the transpositions of these four basic transformations.