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Old 10-16-2017, 12:58 PM   #1
zanshin777
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Default Why half steps in the scales are where dissonance happens?

https://youtu.be/yuhSUZGWC0E?t=210 (Pinpointed Link)

Key : C Major

He says

F (4) wants to resolve to E (3) and B (7) wants to resolve to C (8). Because of Half-Steps.

and he says those half steps are where dissonances happen.

How and why?
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Old 10-16-2017, 03:21 PM   #2
JonR
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Half-steps have the strongest "tendencies", but which way they move depends on context.

In the key of C major, normally F will tend to E, and B to C. But if the chord is F or Dm, then E will resolve up to F. Likewise if the chord is G or Em, then a C will resolve to B.

I.e., it's about chord tones. Dissonance is always in relation to a current chord, and the resolution involves a move to the nearest chord tone (up or down).

An implied harmony - with no actual chords - may be enough. So, you could have a melody using the C major scale, which ends on C. Add an F above that C and it will "want" to resolve down to E.
That is, we want it to resolve, because the melody has told us C is the tonic, while F is the acoustic root of a C-F interval (we perceive that subconsciously). That means F is fighting the established tonal centre. Moving to E creates a consonant major 3rd in which C is the root. C wins, as it were. F could also move up to G (to create a consonant C-G 5th), but E is closer. We also psychologically expect the resolution of tension to be a "descent" of some kind, a "fall" - a relaxation. ("Cadence" derives from the Latin "to fall".)

The additional factor is when F and B occur together, forming a dissonant tritone (as happens in the G7 chord). That makes resolution more urgent. In C major, the interval resolves by the notes moving in opposite directions: F-B opens out to a E-C minor 6th (C is still acoustic root), while B-F closes in to a C-E major 3rd.

But F-B on its own is an ambiguous interval. It could be F-Cb (tritone in key of Gb major), in which case it will resolve to Gb-Bb. This is the basis of the jazz tritone sub.
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Old 10-20-2017, 02:25 PM   #3
zanshin777
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Thank you very much for your detailed answer JonR.
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