Because we naturally hear notes in the context of a key (a tonic note), not as pure raw intervals. A 1-3 major 3rd doesn't "sound like" a 4-6 major 3rd.
learning to hear scale degrees (using movable-do solfege) gives you more bang for your ear-training buck than contextless interval practice.
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Think of moveable do as scale degree training rather than interval training. Interval training is about recognising what a perfect 5th, etc. sounds like; moveable do is about what the 5th scale degree sounds like.
Submitted May 14, 2021 at 09:41AM by maiasub https://www.reddit.com/r/Learnmusic/comments/nc7ojw/is_movabledo_solfege_the_best_way_for_interval/?utm_source=ifttt