Dido and Aeneas in the context of "Henry Purcell"

Diatonic and chromatic are terms in music theory that are used to characterize scales. The terms are also applied to musical instruments, intervals, chords, notes, musical styles, and kinds of harmony. They are very often used as a pair, especially when applied to contrasting features of the common practice music of the period 1600–1900.

These terms may mean different things in different contexts. Very often, diatonic refers to musical elements derived from the modes and transpositions of the "white note scale" C–D–E–F–G–A–B. In some usages it includes all forms of heptatonic scale that are in common use in Western music (the major, and all forms of the minor).

Figured bass is musical notation in which numerals and symbols appear above or below (or next to) a bass note. The numerals and symbols (often accidentals) indicate intervals, chords, and non-chord tones that a musician playing piano, harpsichord, organ, or lute (or other instruments capable of playing chords) should play in relation to the bass note. Figured bass is closely associated with basso continuo: a historically improvised accompaniment used in almost all genres of music in the Baroque period of Classical music (c. 1600–1750), though rarely in modern music. Figured bass is also known as thoroughbass.

Other systems for denoting or representing chords include plain staff notation, used in classical music; Roman numerals, commonly used in harmonic analysis; chord letters, sometimes used in modern musicology; the Nashville Number System; and various chord names and symbols used in jazz and popular music (e.g., C Major or simply C; D minor, Dm, or D−; G, etc.).

Dido's Lament ("When I am laid in earth") is the closing aria from the opera Dido and Aeneas by Henry Purcell to a libretto by Nahum Tate.

It is included in many classical music textbooks to illustrate the descending chromatic fourth (passus duriusculus) in the ground bass. The conductor Leopold Stokowski wrote a transcription of the piece for symphony orchestra. This is played annually in London by the massed bands of the Guards Division at the Cenotaph remembrance parade in Whitehall on Remembrance Sunday, the Sunday nearest to 11 November (Armistice Day).