first species: lines move at same rate; one melody note and one harmony note

rules

only consonants allowed; 3, 5, 6, 8, perfect 5, perfect 8, imperfect major 3, impefect major 6, minor minor 3, 6

no 2, 4, 7, augmented or diminished interval

perfect intervals cannot be approached by parallel motion

perfect fifths and octaves not approached by similar motion unless upper voice moves by one step

voice leading

parallel: melody and harmony move by same interval

similar: meldoy and harmony move in same direction but not same amount

oblique: melody or harmony moves and other doesn't

contrary: melody and harmony move in opposing directions