Perfect fourth

As a fourth ( rarely fourth, from Latin quarta, the Fourth ', ancient Greek Diatessaron [ διά dia τεσσάρων tessaron ], every fourth ' or ' all four ' ) is called in music an interval that spans four pitches of a diatonic, heptatonic scale (e.g. C → F). In a narrower sense is meant by the fourth and the fourth tone of a musical scale. The fourth includes in its pure form five, in their versions, four or six half-steps. The fourth is the complementary interval to the fifth.


The fourth may occur in three variants:

  • The perfect fourth (a ) having the frequency ratio 3:4 in the natural atmosphere is most common. It takes place in all kinds of music frequent use, furthermore, as the German siren tone sequence or fanfare at the carnival. Depending on the musical context, the fourth is treated as a consonance or dissonance. In the classical counterpoint the fourth is classified as dissonant. In the theory of harmony, for example, in the six-four chord fourths are considered urgent above the root than on the resolution, so too dissonant. In polyphonic sentence but occur quite fourths, which are perceived to be consonant, eg in C major chord cegc ' the interval g -c'. As a single phenomenon is typically perceived as a consonant.
  • Called the augmented fourth ( b ), also tritone, presented as one hand occurs between the fundamental tones F and H, on the other hand is considered dissonant, long time tonsystematisches problem ( " diabolus in musica " ) and has been called or after the Middle Ages considered inappropriate;
  • The diminished fourth ( c ) has a meaning in the major-minor system only with consideration of their enharmonic mismating with the major third.

The Lydian fourth is the characteristic interval of the Lydian scale. In the Lydian scale is between the root and the fourth stage, in contrast to the perfect fourth in ionic scale, an augmented fourth.


  • Fourth upward C -F? / I
  • Fourth down C G? / I
  • Augmented fourth ( tritone ): up C- Fis? / i
  • Downstream C -Ges? / i