iternabe This is just my view for what it's worth.
Music theory without ear training is ... well, odd. Musitc theory is just a description of what's going on musically, a way to describe what you're hearing. So you don't just memorize a bunch of mathematical combinations, you learn to give a name to the chords, scales, etc., that you're playing.
Just like when you learned simple major and minor chords and scales. You probably played them and heard the difference. Then when you heard them later, you said "Ah, that's a major / minor chord / scale." So, just that. But more. 🙂
Sus4 chords in particular are often used in a way that the 4th resolves to the 3rd. Play that bar over and over and you'll hear what I mean. Then you'll hear it again someday in a different context and go "Ah, sus4." 😃
