Inside that family each chord does one job. 1 is Home — where the song rests, where it starts and ends. 4 is Away — one step off the porch, restless but safe. 5 is the Question — strummed on its own it's just another bright chord, but land on it AFTER Home and the music hangs mid-air, a sentence missing its last word. That hanging-ness is what musicians call tension: it lives in the situation, not in the chord. The grown-up names for the three jobs are the tonic, the subdominant, and the dominant — but you don't need those words to feel them.