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I just started my journey of music, and I am wondering if the possible choices for chord sequence can be many given a progression, according to music theory.

I am worried about using the wrong or misleading terms here. To be more specific, given the popular progression 1-4-5, can we find many different chord sequences (also consider inversion and not necessary triad) which are correct and reasonable in key of C? E.g. C-F-G, C-Fm-Gm and C/E-Fm-Gm all sound good IMO, so I am curious if there are something related to music theory.

EDIT:

I am considering a particular scenario where one figures out chord sequences without any melody provided, which means there is no constraint for chord sequences imposed by melody. The only limitation is the given 1-4-5 (or any other like 1-2-5, 1-2-7, 6-4-5, etc.) in one key.

note: I avoid using I-IV-V because it refers to the specific Cmaj-Fmaj-Gmaj in key of C. On the other hand, 1-4-5, though informal, makes generality because it only fixes the roots but not chord types (triad, seventh, major, or minor, etc.). Sorry I am just a beginner, lots of misleading terms here.

  • Fm and Gm are not in the key of C. What is the difference between a “sequence” and a “progression” in your question? – Todd Wilcox Jun 14 '18 at 6:41
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    @ToddWilcox - I often use Fm and Gm when playing in C. – Tim Jun 14 '18 at 6:54
  • @ToddWilcox Maybe I am misunderstanding something. I thought that when one says 1-4-5 in key of C just decides the mapping of 1:C, 4:F and 5:G, and doesn't rule out chord components that are not on C scale, e.g., Ab in Fm, and Bb in Gm. For the "sequence" and "progression", I was referring the former to a specific chord sequence like C-F-G-C, and latter to 1-4-5-1. I am sorry for using the wrong terms. – Francis Jun 14 '18 at 7:28
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    That sounds like you use progression and sequence as interchangeable terms. Do you actually mean, for example, can I-IV-V in C be either C-F-G or C-Fm-Gm ? If so, yes, of course the changes will work, but it's then as different as playing C- Dm-Em, or C-E-A. – Tim Jun 14 '18 at 7:35
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    @ToddWilcox - I wonder. There are many songs 'in the key of C' that contain non-diatonic chords such as the aforementioned F. To me, they're still songs in the key of C. What else could they be called? – Tim Jun 14 '18 at 16:12
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Pretty well any chords can and are used in chord sequences. But - if you are referring to chord sequences over a particular melody, then the choices become limited. It's fairly apparent that underlying chords have some relationship to that melody - chord tones feature very often. So, given a set of notes, and their relationship to each other, chords are somewhat predetermined.

A simple example cropped up the other day, someone said about 'Do, a Deer' that although it uses mainly do, ray, mi etc., you can't play a do (C) chord over do, then a ray(D) chord over ray, and a mi(E) chord over mi.

Given extra info., adding extensions happens quite often. Instead of playing bog-standard C-F-G, it gets added to with something like Cmaj7-Fmaj9-Gm7, which would then lead to F in some cases. Some extended chords in a sequence will tend to dictate what follows - here, the Gm7 has elements of C9, which pushes the harmony through the dominant of F, to F.

  • Thanks! I was not referring to harmonizing a particular set of melodies. In fact, I consider a scenario which is to harmonize a given 1-4-5 (or other like 3-4-5) with chord components (can be triad or 7th, major or minor, different chord types I am saying) . – Francis Jun 14 '18 at 7:34
  • Cool! So when the simple 1-4-5 in C, as C-F-G , is extended to Cmaj7-Fmaj9-Gm7, F would probably take over the tonic; Gm7 leads the progression to rest in F, which changes the key. If so, we might not see such an extension in a song written in constant C, is it correct? – Francis Jun 14 '18 at 7:53
  • No. In jazz, more often than not, C-F-G gets morphed into Cmaj7, Fmaj7, G9, as an idea. The Gm, or Gm7 would take us to an F chord, but no reason why it should modulate the whole piece into F. There are a lot of songs in C which have the middle 8 going to F (I>IV), but all that means is gone to the IV chord, not moved to another key. They usually end with V, taking the song back to another verse starting on - guess - I (C). – Tim Jun 14 '18 at 7:58
  • I see. So V can play the role (depends on its extension, m7 in this case) to drive to IV, and maybe follows the repeat of V-IV-V-IV-V.. and go back to I, staying in the same key. – Francis Jun 14 '18 at 8:05
  • " then the choices become limited" … well, it depends. I once wrote a set of 64 variations over the bass line of Pachelbel's canon (D A B F# G D G A and repeat ad nauseum) each of which had a different set of harmonies - and most of them weren't "in the key of D major" either. – user19146 Jun 14 '18 at 13:09
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Basically, if one uses only I, IV, and V, then there's no way to put those into a pattern that won't make much sense. There's just too few combinations to really get anything to sound objectively unusual. If you consider, say, all the diatonic triads, you can really mke some weird progressions, ie. ii-vi-V-IV or something rather unusual. The more chords you consider, the more possibilities. For example, considering the two chords I and V. If one uses I-V, then it seems to ask a question, setting up what the cool kids call a half cadence. However, switching the order and moving from V-I yields a different feeling, as if one has arrived at a destination. In general, The more chords you use, the more ways to use them, and the order really changes their effects.

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1, 4, 5 (more usually notated with Roman numerals, I, IV, V) in C are C major, F major and G major. Anything else wouldn't be I, IV, V. You can certainly extend or substitute those chords to make something that does the same job as I IV, V - a tonic, a pre-dominant and a dominant. But then you'll have to name them as what they are, which won't be I, IV, V any more!

ii or ii7 (thats Dm or Dm7) are common substitutes for IV. Db7 is a common substitute for G7. So I, IV, V could become I, ii7, bII7 (C, Dm7, Db7). But it won't be I, IV, V any more.

A 'progression' IS a 'chord sequence'.

  • Where's pre-dominant come from? Subdominant sounds so much more apposite! – Tim Jun 14 '18 at 9:32
  • Haven't you come across the term? It describes 'any chord which normally resolves to a dominant chord'. Not just the subdominant. And the question was about what chords OTHER than the subdominant could precede the dominant. en.wikipedia.org/wiki/Predominant_chord – Laurence Payne Jun 14 '18 at 9:36
  • I have, it's just the phrasing of that sentence, which I read as I=tonic, IV=predominant, V=dominant. Re-read, with the next, it makes sense. Apologies. – Tim Jun 14 '18 at 10:53
  • Thanks, seeing things from perspective of chord function indeed gives flexibility and alternatives. Though my question is limited to changing type of chords fixed in 1-4-5. – Francis Jun 15 '18 at 1:42
  • You are perfectly at liberty to write either major or minor chords rooted in 1, 4 and 5. Or augmented, diminished, 7th, 9th etc. etc. chords come to that. But I, IV, V in a major key are all major triads, and if you want the I, IV, V effect, stick to that. – Laurence Payne Jun 15 '18 at 11:21
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There are lots of options. The purpose of chord sequences is to harmonize melodies (in the classical sense) but modern music typically goes the other way. You will learn more as you go, but theory is secondary to sound. If a sequence of chords "sounds good" then compose using that sequence.

Staying in a particular key, a basic rule or guideline from classical harmony theory is that melodies based on the major scale can be harmonized using only the I IV and V chords. These chords cover the notes of the scale. This is why the I-->IV-->V sequence is so useful (though sometime you don't follow this exactly as you may have I-->IV-->I-->V, etc).

There are relationships between the chords that naturally occur in a scale. First, in any key you naturally have the following triads on each degree from Do to Ti (I to vii), I maj, ii min, iii min, IV maj, V maj, vi min, vii dim (maj = major, min = minor, dim = diminished). These are related in pairs by (I, vi), (IV, ii), and (V, iii) just for starters. The 6th degree defines the relative minor key to the major key on the 1st degree. In fact the vi can be used as a substitute for the I, and likewise for the other pairs. There are other chord parings that lead to substitutions and whether or not a substitution works depends in part on the motion of the individual intervals from one chord to the next, as well as the melody. So the short answer to your title is yes, there are many alternatives to a given chord sequence.

  • Thanks! Maybe my scenario is quite opposite to classical composing: figuring out chord sequence before or without melodies. And seeing things with "pairs" (which I believe it refers to chord function, and iii in (V, iii) should be instead (V, viii) ?) gives alternatives. However I would like to stick to a fixed 1,4,5 in one key and see if I get many possible combinations of chord sequences, differences in terms of chord type (triad, seventh, major, minor, etc.). – Francis Jun 15 '18 at 1:56
  • No, I meant V and iii. They are related the same way as I and vi. There is a relation between V and viii but again that was not my intention. The pairs I pointed out all involve a maj chord and its relative minor (all in the same base key of the I chord). The relation is very strong as a I maj6 chord is identical to the vii min7, and same for IV maj6 and ii min7, and V maj6 and iii min7. It's not a substitute but and exact replacement using inversions. Once you realize they are related the exactness can be relaxed and more extensions added. – ggcg Jun 15 '18 at 3:09

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