Species Counterpoint	Theory Things  William Wieland
Melodic Motion in the Counterpoint — mostly stepwise — Do not immediately repeat pitches. — You may write 3rds, P4s, P5s, mi6s (ascending only), and P8s. — Precede and follow large leaps by step in the opposite direction.   (P5, mi6, and P8 are large leaps.) — If you write 2 leaps in a row in one direction,   outline a major or minor triad. — Write no more than 2 leaps in a row in one direction. — Do not write an exposed tritone. — Use the highest and lowest note only once. Counterpoint principles common to all species — Usually begin with a P1 or P8 between the 2 parts.   You may also begin with a P5 above the cantus firmus. — Keep the 2 parts within a 10th of each other. — Favor contrary motion. — Write no perfect parallel motion. — Write no more than 3 parallel 3rds or parallel 6ths in a row. — You may write in similar motion to a 3rd or 6th,   but not to a perfect or dissonant interval. — End with a P1 or P8. — End “ti–do” in one part and “re–do” in the other. Exception: If E   is the final pitch, end “F–E” in one part and “D–E” in the other.	First Species — all whole notes (except the last note) — Write only consonances: P1, P5, P8, mi3, M3, mi6, and M6. Second Species — all half notes (except the last note) — You may begin with a half rest. — In addition to consonances, you may write   passing tones and neighbor tones on weak beats. — Do not write parallel unisons, fifths, or octaves   on successive downbeats. Third Species — all quarter notes (except the last note) — You may begin with a quarter rest. — In addition to consonances, passing tones and neighbor tones,   you may write nota cambiata and double neighbor tones. — Begin each measure with a consonance. — Do not write parallel unisons, fifths, or octaves   on successive downbeats. Fourth Species — all half notes tied across the barlines     (except the last note) — Begin with a half rest. — In addition to consonances, you may write suspensions,   • 7-6, 4-3, and (rarely) 9-8 above the cantus firmus and   • 2-3 and (rarely) 4-5 below the cantus firmus.   (In all suspensions, write the dissonance on a downbeat.) — Precede the last note with an untied half note.
Open Music Theory is a great online resource.