Perfect fourth

An example of a perfect fourth is the beginning of the "Bridal Chorus" from Wagner's Lohengrin ("Treulich geführt", the colloquially-titled "Here Comes the Bride").

The Herald Angels Sing" and "El Cóndor Pasa", and, for a descending perfect fourth, the second and third notes of "O Come All Ye Faithful".

In common practice harmony, however, it is considered a stylistic dissonance in certain contexts, namely in two-voice textures and whenever it occurs "above the bass in chords with three or more notes".

In the 13th century, the fourth and fifth together were the concordantiae mediae (middle consonances) after the unison and octave, and before the thirds and sixths.

[4] Modern acoustic theory supports the medieval interpretation insofar as the intervals of unison, octave, fifth and fourth have particularly simple frequency ratios.

In medieval music, the tonality of the common practice period had not yet developed, and many examples may be found with harmonic structures that are built on fourths and fifths.

The Musica enchiriadis of the mid-10th century, a guidebook for musical practice of the time, described singing in parallel fourths, fifths, and octaves.

In the example, cadence forms from works by Orlando di Lasso and Palestrina show the fourth being resolved as a suspension.

The Austrian composer Johann Fux published in 1725 his powerful treatise on the composition of counterpoint in the style of Palestrina under the title Gradus ad Parnassum (The Steps to Parnassus).

The blossoming of tonality and the establishment of well temperament in Bach's time both had a continuing influence up to the late romantic period, and the tendencies towards quartal harmony were somewhat suppressed.

Still, there are many examples of dense counterpoint utilizing fourths in this style, commonly as part of the background urging the harmonic expression in a passage along to a climax.

Mozart in his so-called Dissonance Quartet KV 465 (Listen) used chromatic and whole tone scales to outline fourths, and the subject of the fugue in the third movement of Beethoven's Piano sonata op.

Fourth-based harmony became important in the work of Slavic and Scandinavian composers such as Modest Mussorgsky, Leoš Janáček, and Jean Sibelius.

Even in the example from Mussorgsky's piano-cycle Pictures at an Exhibition (Избушка на курьих ножках (Баба-Яга) – The Hut on Fowl's Legs) (Listen) the fourth always makes an "unvarnished" entrance.

Examples are found in Debussy's orchestral work La Mer (The Sea) and in his piano works, in particular La cathédrale engloutie (The Sunken Cathedral) from his Préludes for piano, Pour les quartes (For Fourths) and Pour les arpéges composées (For Composite Arpeggios) from his Etudes.