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When textbooks explain why parallel (consecutive) fifths are forbidden, they always say that it undermines the voice independence.

I disagree with this, though.

If voice dependence is the reason for not using parallel fifths, then why composers never use parallel fifth even if the music is NOT contrapuntal? Composers always double different parts in octaves, NEVER in fifth, even though both intervals destroy voice independence.

There MUST be some other reasons why parallel fifths are banned. Could anyone suggest other reasons?

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    Power chord spamming doubles music at the fifth all the time. – Dekkadeci Jan 6 at 7:50
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    @Dekkadeci That's not applicable, because the music you describe isn't following any classical rules anyway. – Ma Joad Jan 6 at 8:06
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    @MaJoad: But the effect of parallel power chords works well precisely because the parallel fifths accentuate the feel of a "single voice" moving together, rather than two independent ones. It's a standard example of why you might not want to follow the parallel fifth prohibition, if you want a different sort of effect. – Athanasius Jan 6 at 17:54
  • Parellel fifths come from organum. They are clasiscaly banned in both four-part harmony and counterpoint. – Marquis of Lorne Jan 7 at 9:45
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    You are misquoting the rule it is parallel fifths that are the problem, not perfect fifths. – Neil Meyer Jan 8 at 7:55
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As brought up in comments, there are plenty of examples of music styles where parallel fifths are appropriate. Parallel chords and even naked parallel fifths are used to great effect in a number of popular styles (and some music around the world) to create precisely the effect of a single "voice" moving in a mass, rather than independent voices.

I gather the OP is more concerned with the fact that the so-called "classical style" seems to contain few parallel fifths to give a sense of voice "doubling," while parallel octaves are used all the time for voice doubling.

First, it should be noted that prohibitions against parallel fifths go back to late medieval vocal polyphony, where octave doubling in parallel was rare. Both parallel octaves and parallel fifths were eventually prohibited in that style to create independence. By the time we get to early renaissance music (mid-15th century), parallel fifths had become quite rare in the notated styles of the time. Historically, the rationale against parallel fifths definitely was rooted in independent voices.

The reason why later composers who adopted octave doubling didn't also adopt "fifth doubling" is probably because perfect fifths have a more distinctive sound. Composers who had been trained in the traditional method of avoiding parallel fifths (and the specific sound it created) were thus less likely to make deliberate use of them except for effect. (Basstickler's observation that parallel fifths for doubling could result in more dissonance/clashes with other voices, whereas octave doubling does not, is another reason they didn't become regularly used. One limits the consonant harmonic possibilities a lot more by trying to double fifths than by doubling octaves.)

And composers certainly did make use of them for effect. Parallel fifths show up here and there in romantic period music and later, often to evoke "folk" or "rustic" styles of music (where parallel fifths were presumably common, as they continue to be in many popular styles today; unfortunately a lot of this music was likely not written down). Later, they came to denote other "exotic" music styles, from medieval to "Eastern" musics. While octave doubling was accepted as a practical technique for allowing different instruments to play the same melody, the more unique sound of fifth doubling was instead employed to evoke specific styles (often those which would not be considered a "learned" contrapuntal style).

Lastly, I'd just note that the prohibition of parallel fifths in classical style is not absolute (pace music theory textbooks that oversimplify things). Brahms was known to carry a notebook around of examples from the standard repertoire. One can find sporadic examples of parallel fifths in Bach, for example. The standard uses tend to occur around cadential formulas, where two voices are both doing standard cadential melodic gestures, but because of rhythmic displacements ("non-harmonic tones") the motions sometimes happen to line up and create parallel fifths. These are not generally noticeable, and Bach wasn't usually concerned about them, because the voices were all following standard cadential melodic gestures that dictated the drive toward the cadential resolution. All other voice-leading concerns were generally subservient to the cadential formulas. (Overzealous editors who were trained in harmonic rather than melodic formulations of cadential progressions sometimes have "edited out" these parallel fifths in Bach, so they're perhaps not seen as often as Bach actually wrote them.)

There is, however, one example of classical usage that could be marshaled to argue for a potential place for "fifth doubling," i.e., in the resolution of the German augmented sixth chord, where some 18th-century composers and many 19th-century composers tended to employ fifths moving in parallel with the bass. (These are sometimes called "Mozart fifths," though I don't know Mozart used them more than other composers.) One could argue that the strong resolution of the augmented sixth interval draws the listener's attention, thus "excusing" the parallel fifths, as the voice-leading of the augmented sixth takes precedence. But it's also true that the parallel fifths reinforce the bass descending semitone motion that is so essential to the augmented sixth chord. (I'm not going to go so far as to claim the German augmented sixth resolved this way was the 18th-century version of a "power chord," but... well, it sort of was.) Composers could only get away with it because the distinctive sound of parallel fifths was obscured in this case by a stronger intervallic resolution occurring at the same time.

But perhaps rather than "excusing" so-called "Mozart fifths," we might question why composers felt the need to use them at all, given the strong prohibition elsewhere. I think it's likely some of the reason why they were deemed acceptable was precisely because of the use of the augmented sixth for very strong half cadences, and the parallel fifths were a sort of "doubling" that made the bass resolution feel even stronger (i.e., not independent voices).

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  • Interesting, when I was learning about the G+6, I don't recall hearing much about this approach. They may have taught it and I forgot but either way, I don't intend to say that you're incorrect or anything like that. We were just taught to have a cadential 64 preceding the actual dominant to avoid the parallel fifths. – Basstickler Jan 6 at 18:54
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    @Basstickler - well, "Mozart fifths" in this sense are a thing. I'm actually somewhat curious about the repeated assertions everywhere (including that Wikipedia entry) that composers resolve the German+6 "almost always" to the cadential 6/4. I wonder if anyone has actually done a statistical analysis of this, or whether (like the overzealous editors who have "corrected" Bach's parallel 5ths) one just assumes that composers "almost always" avoided the fifths by going to a 6/4. – Athanasius Jan 6 at 19:01
  • Medieval prohibition against parallel fifths? Organum is from the Medieval period. – Michael Curtis Jan 9 at 19:42
  • Resolving a German augmented sixth directly with parallel fifths doesn't seem to be a effort to introduce parallel fifths. It's just abandoning the concern for a rule from an old style that no longer applies. (Or even more obviously, simply not wanting the sound of a cadential 6/4. Why be forced to use it if you don't want it.) At any rate, when tastes changed, composer just used parallel fifths with absolutely no concerns for old church style. Liszt and Debussy provide good examples of those changes in taste – Michael Curtis Jan 9 at 20:10
  • @MichaelCurtis: Point taken, but I wasn't really claiming it was a positive effort to introduce parallel fifths. Instead, perhaps composers didn't mind them as much because they may have actually reinforced the strong bass motion (but were hidden enough by the other intervals going on to be "excused"). And there are alternatives to the cadential 6/4: in many cases, composers staggered the resolution of the voices (perhaps to avoid the parallels), but we have plenty examples of fairly "rule-following" composers who still use parallel fifths in this instance. It's just an interesting aberration. – Athanasius Jan 9 at 22:03
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Voice leading and voice independence are not specific to contrapuntal music. Homophonic music of the Classical genre continued to use the voice leading rules of the contrapuntal music that preceded it to preserve voice independence because it provided fuller sounding harmonies. The voices in homophonic music are not thought of as independent melodies, like contrapuntal music, so I can see how one might not think of them in the same manner.

Take a look at some of the Classical repertoire, particularly the Classical era, and notice how often the harmonies are just I-IV-V, yet the harmonies feel rich and full, providing strong support to the melodies. This is in large part due to the voice leading. If you were to take a piece or section that primarily uses I-IV-V harmony, then arrange this to be played on a guitar, utilizing on barre chords (which contain lots of parallel fifths and octaves), you would find that the harmonies are not quite as satisfying, or rich and full sounding.

Speaking to your thoughts on doubling, the idea there is that the doubled line is not considered its own voice; it is just additional texture added to the fundamental voice. Depending on how the harmony and melody interact, doubling with fifths could add a lot more dissonance. Fifths also have a different affect on the harmony, where they can make things feel thick (for lack of a better word), particularly in lower registers. This can make things feel cluttered or dense, where octaves have a more pure sound to them, less likely to add that feeling of clutter.

Modern popular music largely ignores these voice leading rules, which creates a different sort of texture. The consistent use of parallel perfect intervals from chord to chord creates a different sort of accompaniment, often having that more dense feeling I reference above. Heavier rock music (grunge, metal, etc.) often uses power chords (root, 5, octave), entirely omitting the third from the harmony. This creates a very thick, dense sound, helping to create the heavy feeling they are going for.

Even though we tend to find that modern popular music doesn't utilize traditional voice leading, it still comes up sometimes, particularly when any sort of orchestration is added. I was arranging some orchestration for a pop rock song and found myself wondering why the harmonies didn't feel right at one particular moment and I realized it was because of a parallel perfect intervals, which were not present before or after that moment. The rest of the arrangement (guitar, bass, keys) were not concerned with traditional voice leading, using lots of parallel perfect intervals, yet the orchestration basically required it.

In short, homophonic music of the Classical genre tends to stick to the voice leading rules of counterpoint to provide richer, fuller harmonies, and doubling of voices is very much concerned with how the overall texture will be affected and what sort of dissonance(s) it may create.

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    “you would find that the harmonies are not quite as satisfying, or rich and full sounding” – many a guitarist would disagree... – leftaroundabout Jan 6 at 18:09
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    @leftaroundabout - Perhaps that's not the best way to describe what I'm trying to say. I think the difference between barre chord accompaniment, or other harmonies with parallel perfect intervals, is rather profound. Barre chords are not bad or dissatisfying and don't fail to provide a functional harmonic accompaniment, it's more so that use of Classical voice leading seems to have a richer, fuller sound. If you gather what I am getting at, would you have another way to describe this that may be less subjective? – Basstickler Jan 6 at 18:47
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If voice dependence is the reason for not using parallel fifths, then why composers never use parallel fifth even if the music is NOT contrapuntal?

I think you need to describe music more specifically than: "is NOT contrapuntal."

The matter isn't really about whether something is or is not contrapuntal per se, like is the music a fugue, but whether the harmonic style is based on the old counterpoint style. Early Mozart isn't normally considered contrapuntal, but the harmony did follow the old counterpoint voice leading conventions. Parallel fifths weren't the norm for that early classical style as the style's harmony was still rooted in counterpoint. Move ahead in time to something like Debussy's impressionism and the harmony severed the link back to the old counterpoint style. You can see counterpoint (linear independence) on display in some impressionistic works, but you don't see the prohibition against parallel fifths. That change in taste for parallelism wasn't a matter of linear independence, it was about abandoning an old harmonic style.

Composers always double different parts in octaves, NEVER in fifth, even though both intervals destroy voice independence.

Again, the matter isn't about voice independence. Doubling of parts in octaves versus some other interval is a harmonic matter.

If you double in octaves, nothing changes harmonically.

Double a part in (I assume you mean parallel) fifths, and you quickly run into harmony issues where the extra part brings in new tones. That isn't necessarily a problem, but doubling in octaves and doubling in perfect fifths are in no way harmonically interchangeable.

There MUST be some other reasons why parallel fifths are banned. Could anyone suggest other reasons?

You might rephrase the question as: "why do parallel fifth destroy voice independence, but not parallel thirds?"

I would give two reasons.

The first is pure theory. Thirds come in two varieties major and minor, but perfect fifths are only one interval quality. Parallel thirds more properly should be called similar motion thirds which by definition are more independent than parallel perfect fifths.

But I don't that is the really important reason for the prohibition against parallel fifths. For a long time parallel fifths were perfectly fine... in medieval organum. When the contrapuntal styles evolved I think it wasn't a logical, theoretical concern to avoid parallel fifths, but the desire to not sound like parallel organum that was the reason to prohibit parallel fifths.

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    I've always related the avoidance of parallel perfect intervals to the overtone series. Since the fifth and octave are so closely related to the fundamental, they more easily blend with it to be obscured. Thirds are far enough removed from the fundamental that even parallel thirds of the same quality, eg, parallel major thirds, are unlikely to blend into the fundamental. I'd also note that the move to just and equal temperament would further separate thirds from the fundamental as a result of them being further removed from the natural overtones, where fifths were either exact or very close – Basstickler Jan 6 at 19:01
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    Honestly, the first way I was introduced to the parallel fifths prohibition was simply: "parallel fifths are prohibited." The more sophisticated teaching about voice independence feels like a rationalization for the old style. It's a nice way to rise above blind adherence to a rule. But it's so much simpler to just admit it's a matter of taste. In some styles parallel fifths are essential, in other antithetical. No logical or theoretical explanation is necessary. – Michael Curtis Jan 6 at 19:15
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    @MichaelCurtis Taste may be more important than we generally say, however, the voice independence is not just a myth. I've experienced it in my own writing, as mentioned in my answer. I have long criticized the academic approach to teaching theory, where all too many people walk away from those classes thinking of everything as rules, particularly without specification that those rules are specifically for the style of music they are studying. So many questions on here where you can tell the OP wasn't taught about this distinction. – Basstickler Jan 6 at 21:10
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    I’ve found the passage on page 26ff in Studies of Harmony and I’ve posted a second answer with the original translation. – Albrecht Hügli Jan 6 at 22:20
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    @Basstickler, I didn't mean to say voice independence is a myth. On a purely technical level parallel fifths are less independent than parallel thirds. – Michael Curtis Jan 6 at 22:20
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I have asked this question in the same intention right a year ago (my very first question on SE) and I thought to have given the answer I had read in De la Mottes “ “ Harmony”. Well it seems I have posted it elsewhere. But I can’t find it here nor the source.

I know that he says (in other words) concerning forbidden parallel fifths in respect to the organum of fifths:

*Why should suddenly be forbidden what had been for hundreds of years in use - and obviously the only “rule” of voicing two separate parts: the voice leading in parallel fifths of the middle age organon?”

And the answer was ( - apart of the independence of the voices):

”The composers of Ars nova and the following periods wanted to demonstrate that their music was something really new and different as the precedent aera.”

So in this revolutionary motivation lies the will or desire to avoid parallels of fifths.

Add:

I’ve found another one quoting de la Motte:

A look at de la Motte's theory of harmony helps:

  1. The argument of the vibration relationships is nonsensical, because why are quart parallels (2: 3) allowed and quint parallels (2: 3) prohibited?

  2. The bad sound argument is illogical since the fifth is one of the most consonant intervals, the octave anyway. Before Bach, parallel fifths in the organas of Leonin and Perotin were the non plus ultra, after Bach the parallel octaves and later the parallel fifths are found again in music, particularly quickly in instrumental music.

  3. The independence of the voices is not an argument either, because the voice is no less independent when it runs in fifths than when it runs in permitted parallel thirds.

  4. In the end, de la Motte justifies the most important dogma of music with a very flat explanation, but it is at least logical: the ban on parallelism as a reactionary movement, indeed as a deliberate loss and dissociation from the previous one. That's exactly why they found their way back into music.

https://www.clavio.de/threads/offene-quintparallelen-am-ende-von-bwv-564-2.16798/

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If you are doubling at the octave then they are not independent voices. It's just the same voice, at a different octave.
It's not true to say that composers never use parallel 5ths. There are plenty in music - some intentional (Puccini), some not. I even found one in Beethoven once, but can't remember where sorry. At a certain point, most composers gave up caring about such rules.
However, for centuries, composers didn't like the hollow, weak sound of consecutive 5ths and tried hard to avoid them.

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  • The first sentence could be made just as well for fifths, or even any other exact interval, no? – leftaroundabout Jan 6 at 18:05
  • double fifths potential bring in a new pitch class, that changes the harmony, doubled octaves doesn't do that – Michael Curtis Jan 6 at 19:18
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Here are the arguments and the original text by Diether de la Motte and a link to his book:

https://www.scribd.com/document/400639867/The-Study-of-Harmony-Diether-de-la-Motte-pdf

.... parallelisms that actually occur in the music of the great composers.

There are two usual explanations for the prohibition of parallel perfect octaves and fifths between any two voices:

1) The octave has a simple ratio of 1:2 between the frequencies of its lower and upper notes (for example: if the frequency of the lower pitch is 100 Hz., then the frequency of the upper pitch will be 200 Hz.). Because of this acoustical phenomenon, the two tones of the octave are often perceived as a single unified sonority. Similarly, the perfect fifth, which has thenext most simple ratio (2:3) between its upper and lower tones, is also frequently perceived to be a strong unified sonority. Therefore, two voices which move in parallel octaves or perfect fifths will tend to lose some of their own melodic individuality and independence.

*2) Parallel perfect octaves and perfect fifths simply sound "bad."

Both of these traditional explanations are somewhat troublesome. In explanation 1), why are we not also cautioned against the use of parallel perfect fourths the next most simple ratio (3:4)?

and De la Motte argues:

In explanation 2), why is it claimed that parallel perfect octaves and fifths sound "bad," when, as shown in Ex. 1:26, such structures abound in the music of the Middle Ages? (Furthermore, in the style of Medieval parallel organum, the parallelisms in question are said to have a particularly "good" sound.) Example 1:26 Excerpt from a Thirteenth-Century Conductus * Parallel perfect octaves and fifths, broken by rests or cadences, were also generally pemitted and cmployed im later musical styles.

All technical arguments which attempt to explain why parallel perfect octaves and fifths should be avoided create problems that cannot be resolved. For that reason, I shall attempt to explain the origin of this rule a different way. The major triad is a basic harmonic element that was common to Western music during a period of some 500 years (from Dufay to Reger). It also plays a vital role in twentieth-century music, especiallyinthe works of Hindemith and Stravinsky. Dominant-seventh and diminished- seventh chords, which are newer structures than the major triad, are quite rare in twentieth- century music literature, however. This is because both of these sonorities are associated with the kind of dominant-function harmony that is particuarly characteristic of the Classical and Romantic periods. By 1925, many composers refused to employ dominant- or diminished- seventh chords in their works because these sonorities evoked musical styles and aesthetics that were no longer in vogue. In short, harmonies which had played such an important part in the music of the past were simply rejected as old-fashioned by composers of a newer age. Parallel perfect octaves, unisons, and perfect fifths were first considered errors of composi- tional technique in the fourteenth century.

In many ways, compositions of this era also manifest an aversion to earlier musical expressions.

Since composers of the fourteenth century considered the music ofthe previous era to be primitive, it is possible that disdain for and avoidance of earlier techniques helped establish the rule that: parallel perfect consonances are musically incorrect.

Composers always double different parts in octaves, NEVER in fifth, even though both intervals destroy voice independence.

There MUST be some other reasons why parallel fifths are banned. Could anyone suggest other reasons?

Well, as you see, your question provoked some good answers, but eventually not in the sense of your last point!

As now rereading your question I have to say: Never say never!

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If voice dependence is the reason for not using parallel fifths, then why composers never use parallel fifth even if the music is NOT contrapuntal?

Try playing this example.

enter image description here

This is not contrapuntal writing at all. It's homophonic two-part harmony that you could hear in pop music, e.g., a vocal duet. In the first bar, I hear it as though there were two voices, and then suddenly one of the voices went away. It's arguably unpleasant and distracting. It feels like the texture changed suddenly. If the effect the composer wanted wasn't the effect of having one voice disappear suddenly, then this could be considered a mistake or bad writing.

In the second bar, I personally don't hear the disappearing-voice effect anywhere near as strongly when I play it on the piano at a slow tempo, but the same sort of thing can happen with a fifth as with an octave.

All of this can be an issue even if you had no intention at all of writing in a contrapuntal style and didn't care about having a texture of independent voices for its own sake. You create a texture, which creates an expectation on the part of the listener. Then you violate that expectation.

Composers always double different parts in octaves, NEVER in fifth, even though both intervals destroy voice independence.

Doubling parts in octaves is just considered a thickening of the texture. The ear-brain system so closely identifies notes that differ by an octave that they tend to meld together into the same sensation of tone.

The sound of parallel fifths (as opposed to just direct fifths) is different. It's very distinctive and creates, e.g., the effect of monks singing a chant. If that wasn't the effect you wanted, and it was the effect you produced, then it's a mistake or bad writing. But I don't think this effect really stands out to the listener if it's just inner voices or only a couple of fifths in a row.

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Here is an interesting idea that I came up with that I have not seen elsewhere. It involves knowing something about the harmonic series, and also a little bit of signals/electronics theory. It doesn't quite answer the question, but might throw some light on it.

First the harmonic series. If we take the note C1 as root (that's pretty low but it's just to make the numbers easy - things work just the same starting from any note):

5 x F = E3 (F=frequency)

4 x F = C3

3 x F = G2

2 x F = C2

1 x F = C1

So a perfect fifth is 2F and 3F.

Now in signals theory there is something interesting - if we mix two frequencies F1 and F2 through a non-linear element (don't worry what that really means, basically any element that has some distortion will do this a bit) we get out F1, F2 and also sum and difference F1 + F2 and F1 - F2

So when we "mix" our perfect fifth we get

2F = C2

3F = G2

2F + 3F = 5F = E3

3f - 2F = 1F = C1

So the perfect fifth can do something special - it can produce extra overtones that "imply" a full major chord. In fact you can hear this when you hear an electric guitarist play a power 5th through distortion - the "extra" major 3rd above the chord.

Now let's say this happens at low, hard to hear but subtle levels on a piano (try it and see if you can hear the extra notes). You will subtly imply notes that are not in the major/minor scale, which might not sound "quite right".

Of course this doesn't quite explain the "parallel" part of the rule, but I do wonder if it has some bearing on why 5ths are considered a bit "special" in traditional harmony.

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    This is an interesting answer explaining the overlapping overtones. I’ve just edited the first column of the frequencies (like you meant it) as they were in a row ... and defined F= freq. – Albrecht Hügli Apr 2 at 6:01
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There is a divergence of opinions on the matter, power chords are indeed parallel fifths but they should not be considered as such. The power chord is just a simple chord on the guitar, that when played in the lower registers, give a sound that sounds mean, they should not be considered chords in the traditional sense of the word, they are just a fifth played low that gives a sound that appeals to some.

In the case of power chords on the guitar there exist a fundamental choice in guitar players live of is his playing going to be power-chord based or is he going to use the fuller harmonic texture of a barre chord.

If you are playing in a harmonically complex band then barre chords will serve you well, if you are playing in an aggro thrash band you may enjoy the aggressiveness of a power-chord. Neither is better than the other, it is just a choice.

As for the parallel octaves, you may find in piano music this again should not be considered as such. It is one of the stylistic points of the piano as an instrument that the sound it produces has a quick decay and limited senority.

This just means that in effect the pianist has to constantly be playing a lot of notes to get a good sound, what you would see as parallel octaves is just two notes played together as an effect to make a better sound.

And then lastly, you must know the basic rules of harmony is just a guideline, I don't like to think of them as rules. It is just an introduction to the basics of voice leading, you are free to change or bend the rules as you wish. You may find that these rules are not there to stifle your creativity but is just a realisation trough the centuries of musical discovery into what makes good music.

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