Both jazz and rock (and virtually all popular American styles... country, hip hop, etc) put the "boom" on 1 and the "clap" on 2. Regardless of whether that "cla

Both jazz and rock (and virtually all popular American styles... country, hip hop, etc) put the "boom" on 1 and the "clap" on 2. Regardless of whether that "clap" is a high-hat, snare, rim, etc, it's the beat you would clap your hands on. The two approaches you describe ("emphasis on 2 and 4" and "emphasis on 3") are actually the same thing. You're just counting twice as fast when you identify 3 as the back beat vs 2 & 4. To say that another way, any song that can be notated with the snare on 3 could also be notated with the snare on 2 & 4 by halving the tempo. I think most musicians would notate "And Then I Knew" such that the snare falls on 2 and 4, but that could probably go either way. I'd contrast this with classical music (classical as in Mozart), where the emphasis is on beats 1 and 3.