Now, I'll be basically phrasing these like rules, and in a pedagogical sense, they should basically be thought of as rules. You'll notice, if you look at historical examples, that pretty much no one ever followed these rules to the letter. Bach is pretty much credited with writing the rulebook as a study on Counterpoint, and I'm not entirely sure that he ever wrote a piece that followed them completely.
It's important during this lesson to understand exactly what counterpoint is. Counterpoint is a set of, essentially, statistics. They're phrased as rules, but essentially when we say "No parallel fifths" we mean "Common practice music doesn't use parallel fifths". If parallel fifths sound good, then by all means, use them. However, they're likely to sound modal and a little off from normal tonal music. So if you're writing harmonies and don't want the sound of parallel fifths, then you'll know to avoid them without first writing them, hearing how they sound, and changing them.
Basically, if writing music is like taking an essay test, counterpoint is like having a cheat sheet sitting there right in front of your face, with all the relevant information. Just because you have the information doesn't mean you just copy it word for word into the answer, and hell, if you really want you can ignore it all and draw a smiley face instead of the essay. Sure, you'll fail the essay, but why are you taking that class then?
Ok, it's not a perfect analogy, but you get the idea(I hope)
Before we get to the rules, let's go over some terminology:
m3, M3, P5, m6, M6 are "Consonances"
m2, M2, P4, 4+, 5o, m7, M7 are "Dissonances"
"Harmonic tones" are tones which occur as part of the harmonic structure(For instance, in a I chord in G Major, G, B, and D are harmonic tones)
"Nonharmonic tones" are tones which occur outside of the harmonic structure(In a I chord in G Major, A, C, E, and F# are nonharmonic tones)(Also, the chromatic alterations for more nonharmonics, but these are the ones in the key)
Now, with nonharmonic tones, there are two main distinctions, which are "Accented" and "Unaccented". This doesn't refer to the articulation of the accent, but rather whether it falls on a strong beat(1 and 3 in 4/4, for instance) or weak beat(2 and 4 in 4/4)
Also, we have a few different types of nonharmonic tones. Basically, we divide motions into steps and skips, and have a name for each type.
A neighboring tone is a tone that we approach by step that then returns by step to the original note. These are divided into upper neighbors and lower neighbors. As an example:
The starred note is an upper neighbor
A passing tone is a tone that we approach by step and that we leave by step to a different note. ex:
Now, we also have nonharmonics where the nonharmonic becomes a harmonic tone, due to a change in the surrounding harmonies.
An anticipation is a nonharmonic tone where we approach a note in a later chord before the chord happens. Ex:
And a suspension is the opposite, where we hold a note from a previous chord through a second chord.
And now for the super-confusing ones. These are combinations of steps and skips.
An escape tone is a tone that is approached by step, which resolves by skip.
And an appogiatura is a tone that is approached by skip, and resolves by step(I don't have a picture for this one
Step-Step(with same harmonic tone) = Neighbor
Step-Step(with different harmonic tones = Passing Tone
Step-Skip = Escape Tone
Skip-Step = Appogiatura
Hold-Step = Suspension
Step-Hold = Anticipation
Also, let's review the types of motion:
Parallel motion is motion where both parts are moving in the same direction by the same intervals.
Similar motion is motion where both parts are moving in the same direction by different intervals.
Oblique motion is motion where one part is moving while the other is not
Contrary motion is motion where the parts are moving in different directions.
So, let's start talking about the rules now:
For all species, we have the following rules:
1: The tonic at the cadence is to be approached by step. If approached by below, the leading tone must be raised so as to make the final interval a semitone.
2: The melody cannot have sevenths of any kind, nor can it have intervals of an octave or larger. Also, if the melody uses an ascending minor sixth, the next move must be downwards.
3: If the melody has two skips in a row, the bordering interval must be consonant, and the second skip must be smaller than the first.
4: In any combination of three notes, the bordering interval must not be a tritone or a seventh
5: All parts must begin and end on a consonance.
6: Unless necessary, avoid intervals larger than a major tenth
Now, if you look up "counterpoint" on wiki, you'll see those as well as some other rules. Some of these are covered by other rules, and some of these aren't actually rules, just suggestions to make the rest easier. I just mention this in case anyone is wondering why mine differ... it's not that it's an incomplete list so much as things like "Use contrary motion" isn't really a rule of counterpoint, it just makes obeying the other rules of counterpoint super-easy to follow.
Also, in general, outside of nonharmonic tones, parts should remain in consonance.
Now, We'll start with First Species Counterpoint. First Species is two voices, at one note per one note. We go back to early music terminology here, since that's where the roots are. The main melody is referred to henceforth as the "Cantus Firmus" or "C.F." The other parts are the "voices" or "lines".
1: As a bit of a refinement to the "consonant beginning/end", in First species you can only end on fifths, unisons, or octaves. If the added line is below the C.F., it cannot be on a fifth.
2: No unisons, except at beginning+cadence
3: No parallel fifths, or octaves
4: No "Hidden" fifths or octaves(I know, I'll explain it)
5: No more than three consecutive parallel sixths or thirds
So the most flexible and most confusing of those is the "No hidden fifths" thing. What is a hidden fifth(Or octave)? A hidden interval is one that is approached by similar motion. So if the C.F. goes E-G-A ascending then the added line going G-C-F ascending, for instance, would have a hidden fifth, as both approach the C/G fifth from below. The main reason not to do this is that it's pretty damn striking(By this I mean it's unexpected. Say you're walking down the street and some random guy decks you. Pretty unexpected, right? Unless you live in New York City), and is sort of like a lesser version of the parallel fifth.
Now, for the parallel interval rules, also known as like, half of the remaining rules, the main reason we avoid them is because it sounds super modal with fourths(but no fourths anyways... same reason) and fifths, and gets pretty boring with thirds/sixths. Remember the whole Organum Duplum thing, where we just copied melodies offset by a fifth or fourth, and that was an early form of harmony? And now remember how a few refinements after that, the "Sweet British Sound" was the application of thirds? Yeah, so we try to avoid going back to Organum Duplum when writing in tonal music.
Now, wiki says that one rule is to use contrary motion when possible. This isn't a rule, but it is a pretty good suggestion. Notice that with the parallel and hidden interval rules, we have rules governing similar and parallel motion. Also, one of the rules is only the beginning/ending harmony, so we have only one species-specific rule after that that deals with a possibility that occur with Oblique or Contrary motion, which is the "no unisons" rule, and one general rule, which is the "no intervals larger than a tenth" rule. Essentially, as long as you avoid having the parts be too far apart and you avoid unisons, as well as trying to stick to consonances, you will find it almost impossible to break the rules while using oblique and contrary motion. Contrary/oblique motion are counterpoint Jesus.
And that's.... that's pretty much it for first species. So on to second species. Second species starts to get a little more complicated, and it's two notes against every one in the C.F. We divide these into "accented" and "unaccented", again, like nonharmonic tones, the accented one is the one on the beat, the unaccented is the one off the beat. In pure second species counterpoint, this is divided equally. So against whole notes, second species has two half notes.
Second species starts getting a little more complicated here, too, because while the rules of first species pretty much carry over for the accented notes, we also have rules governing the unaccented note and the relationships between them. So for instance, we can't have parallel fifths in consecutive accented beats.
So first off, in second species, we can either start with an accented or unaccented beat in the added line, meaning we can start with a rest, but after that we have to have both notes in the added line played, we can't for instance decide to have a rest mid-counterpoint.
Now for the added rules
1: The accented beats must be consonances. The unaccented beats may only be dissonances in passing tones.
2: Unisons are allowed on unaccented beats, but not on accented ones.
Seems pretty simple, right? The important thing to note with all these additions is that everything just keeps piling on, and we get a lot of situational rules, like the "No unisons" rule that only applies to accented notes in second species but all in first. Also, we get interesting things like oblique motion being possible between accented notes using a consonant neighbor in the added line on the unaccented beats.
Next post we'll go on to 3rd and 4th, then touch a bit on florid(5th species). After that, we can get to some voice leading stuff, and then we'll do the roman numeral chordal theory stuff for a bit.