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I'd like to understand why the second shape is considered to be a P5 ? When I play it I hear a descending P4 or reversed P4 if you will. I try to forget about theory, nine rules, calculation but rely on my ears and I don't recognize a P5 color in this second shape, nor a descending P5.

Thanks for your help


Existing answer are correct but don't really address the question regarding why you hear it that way. That is a matter of training. While it is true that a P4 and P5 are just inversions of each other there is a natural built in tendency to use the lower note as a reference. This may have to do with how the brain is wired and a phenomenon called fundamental tracking but I'm speculating on that.

If you play the notes at the same time you will likely always hear the second shape as a P4 based on my comments above. If you play the upper note first then the lower one you might use the higher note (first played) as the reference or 'Do'. In that instance you would then HEAR a descending 5th since you've tuned your ear to use the first note played as a reference.

Some people will gravitate to the "Lowest Note" in the sequence then start hearing the rest as ascending notes relative to the lower pitch. This happens when taking interval quizzes but is not likely to happen while listening to music since you are not going to buffer an entire song then replay its notes out of order in your head (unless you're Mozart). With training we can learn to hear things differently. What you identify as the interval will depend on which note you hear first but you don't have to use the lowest note as the reference.

  • So according to you, if we hear the "ascending version" of one interval when notes are played at the same time, it has to do with our brain and trainning conditioning rather than something intrinsic to the sound ? – Jack Mongaillard Apr 18 at 22:51
  • I think that someone who knows nothing about theory will spot the similarites between two equals intervals with different pitches but same directions rather than same interval but with ascending and descending directions. What if musically speaking there were more than 12 intervals, as one interval gives two differents colors wether its ascending or descending. Does it make sense ? – Jack Mongaillard Apr 18 at 22:58
  • @JackMongaillard, you are contradicting yourself in your first comment by saying Ascending version where the notes are played at the same time. An interval cannot ascend while having the notes played at the same time. I think we are using the words to mean different things. – user50691 Apr 18 at 23:01
  • @JackMongaillard, also, what I am asserting w/r to notes played in sequence is that the first note we head brain washes us into using that as a baseline for a short duration of time. That is a psychological effect. The other effect involving fundamental tracking was, as I stated, completely speculative. – user50691 Apr 18 at 23:02
  • What I meant by ascending version is lowest note to higher, so I'm asking why in a harmonic interval we hear the ascending color instead of descending one. Conditioning ? – Jack Mongaillard Apr 18 at 23:20

You are right, the interval of the second shape is a P4, not a P5. However, the relationship between the two notes is that the lower note is the 5th of the note labeled “R” for root, assuming you are thinking in terms of chord tones.

  • Assuming R is C and G is the note above, if I play a C chord including that interval it becomes a P5 as C is the root and C to G a P5 ? Therefore what is the difference between inverted P4 (or P5) and descending P4 ? – Jack Mongaillard Apr 18 at 19:14
  • The interval between C and the G above it is a P5. The interval between C and the G below it is a P4. There is a difference between intervals and chord tones. Intervals are the distance between notes but chord tones are the notes that are built over a given root and can be played in any order. Hope this answers your question... – John Belzaguy Apr 18 at 19:20
  • Thank you, so that picture is wrong it should be named inverted P5 (i.e P4) in a chord tone context.. – Jack Mongaillard Apr 18 at 19:33
  • I don’t know the context of what is being shown there but the interval of the second one is a P4. No need to call it an inverted P5. Remember, going up a P4 or P5 is not the same as going up or down from the root to the 5th. Intervals are completely independent of chords, they are simply lines on a ruler. Chord tones use intervals to measure them, for example Root up to 5th is P5, Root down to 5th is P4. – John Belzaguy Apr 18 at 19:54

P4 and P5 are closely related. They are inversions of each other. Let's say your two notes, in the 1st example, are A and E. On any of the bottom 4 strings of the guitar, they could be, on appropriate frets, P5.

Change over, so they're both on the same fret, adjacent strings, they're E and A. So now, the interval is P4. Same notes, but opposite way round. While minor intervals inverted change to major, and diminished to augmented, perfect stay as perfect. So P4 inverted becomes P5, and vice versa.

Something else to consider may be the harmonics produced. The mix heard will differ slightly between E>A P4 and A>E P5.

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