Interordinal: Difference between revisions

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'''Interordinals''' are interval categories halfway between adjacent interval classes of the diatonic scale. For example, 250c is an interordinal because it falls between 200c (the 12edo major second) and 300c (the 12edo minor third). Interordinals may sometimes be called '''interseptimals''';, however the term "interseptimal" also has certain other senses on this wiki.
'''Interordinals''' are interval categories halfway between adjacent interval classes of the diatonic scale. For example, 250c is an interordinal because it falls between 200c (the 12edo major second) and 300c (the 12edo minor third). Interordinals may sometimes be called '''interseptimals''';, however the term "interseptimal" also has certain other senses on this wiki.


There are usually considered to be four interordinal regions: '''semifourth''' (between major 2nd and minor 3rd), '''semisixth''' (between major 3rd and perfect 4th), '''semitenth''' (between perfect 5th and minor 6th), and '''semitwelfth''' (between major 6th and minor 7th). [[19edo]], [[24edo]], and [[29edo]] are notable edos with a complete set of interordinals; the MOS scales manual (5L1s) and semiquartal (5L4s) (when generated by a semifourth) do as well. Notable JI interordinals include 15/13 (a semifourth) and 13/10 (a semisixth).
There are usually considered to be four interordinal regions:
# '''semifourth''' (between major 2nd and minor 3rd)
# '''semisixth''' (between major 3rd and perfect 4th)
# '''semitenth''' (between perfect 5th and minor 6th)
# '''semitwelfth''' (between major 6th and minor 7th).
[[19edo]], [[24edo]], and [[29edo]] are notable edos with a complete set of interordinals; the MOS scales manual (5L1s) and semiquartal (5L4s) (when generated by a semifourth) do as well. Notable JI interordinals include 15/13 (a semifourth) and 13/10 (a semisixth).


The following table shows various ways to name interordinals:
The following table shows various ways to name interordinals:

Revision as of 19:59, 12 February 2026

The interval regions surrounding neutral (blue) and mosdiatonic (red/yellow) intervals. Interordinal regions are the "gaps" in this scheme.

Interordinals are interval categories halfway between adjacent interval classes of the diatonic scale. For example, 250c is an interordinal because it falls between 200c (the 12edo major second) and 300c (the 12edo minor third). Interordinals may sometimes be called interseptimals;, however the term "interseptimal" also has certain other senses on this wiki.

There are usually considered to be four interordinal regions:

  1. semifourth (between major 2nd and minor 3rd)
  2. semisixth (between major 3rd and perfect 4th)
  3. semitenth (between perfect 5th and minor 6th)
  4. semitwelfth (between major 6th and minor 7th).

19edo, 24edo, and 29edo are notable edos with a complete set of interordinals; the MOS scales manual (5L1s) and semiquartal (5L4s) (when generated by a semifourth) do as well. Notable JI interordinals include 15/13 (a semifourth) and 13/10 (a semisixth).

The following table shows various ways to name interordinals:

Interordinal nomenclature
24edo interval "semi" names "inter" names "ultra"/"infra" Greek-derived names
250c, 5\24 semifourth second-inter-third ultramajor second
inframinor third
chthonic
450c, 9\24 semisixth third-inter-fourth ultramajor third
infrafourth
naiadic
750c, 15\24 semitenth fifth-inter-sixth ultrafifth
inframinor sixth
cocytic
950c, 19\24 semitwelfth sixth-inter-seventh ultramajor sixth
inframinor seventh
ouranic
Interval regions
Unison (JND region) Comma Quartertone Semitone Neutral second Major second Inframinor third Minor third Neutral third Major third Ultramajor third Fourth Semiaugmented fourth
Tritone Semidiminished fifth Fifth Inframinor sixth Minor sixth Neutral sixth Major sixth Ultramajor sixth Minor seventh Neutral seventh Major seventh Ultramajor seventh Octave