Although this has nothing to do with historical theory, I do always look for the linear descent to the final when marking out a harmonization. Amost all Western music has it. In historical theory, the final itself will normally be an indicator of mode. Some renaissance and baroque music begins and ends in a different key, and you have to look out for that, but normally the final, then the mode, will give you a starting, stopping, and cadence point. Then using the rule of 1, 3, 5, 6 in alternation, try those bass notes that many steps down from the main profile center of the tune to map out your bars. dt
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