In chord building 1 I talked about the scale, and unfortunately we will have to look at it a bit more before we can go much further with this subject.
The scale I talked about was the most common type - the major scale. Luckily, this is the only scale we need to know for the moment. It has eight notes and they are numbered 1 to 7, and the last one is normally called the 'octave' (from Latin meaning eighth). CDEFGABC, for instance, is the scale of C, and GABCDEF#G, for a reason that I hope will become apparent in a minute, is the scale of G. The numbers of the notes in a scale are called the 'degrees' of the scale - that is, if C is the first, then D is the second, and so on - to and beyond the eighth.
Of course, if you start at G and work upwards you will still get first, second, third, etc., but they will be the notes in the scale of G. So G will be the first, A the second, and so on. The same rule will apply no matter what note you start on even if for some unfortunate reason you find yourself needing to work something out in F# (otherwise known as Gb) or some other annoyingly awkward key.
The reason the scale of G has F# and not F natural (as an ordinary F might be called) is that a scale has fixed distances (called intervals) between the notes, so that if C scale goes C - tone - tone - halftone - tone - tone - tone - halftone (count it out) then so must G, and if you count out the G scale I have quoted you will find it does do that same thing, and that as a result it has an F# immediately before the top G. You also might like to try playing it with F natural instead and see what it sounds like. I expect you will conclude that it is a type of scale, but not the same type as the C one, and you may not find it sounding quite how you would like it to sound.
Now we should look at some intimidating chord name, like C9b5 (C9th with flattened fifth), and translate it into digestible language.
It is made like this:
C E Gb Bb D
(Academic types might wish to argue with this, because the intervals described by these numbers are all from the root and they are not always described thus in music colleges - but this is what we are doing here)
The reason for the name of this chord is that it is a C chord that has been added to and altered, and the numbers refer to the 'degrees of the scale' of the notes in it -
that is, the G is the 5th note in the C scale, and it is going to be played flat (b5 in C = Gb) instead of 'natural', and so on........
So what about the 9th? The ninth is the note after the octave (the octave is, of course, the eighth) - that is, it is D - the very D we are going to play in our chord. The E following that would be referred to as the 10th, the F the 11th., and so on, but we are not using them (at least for the moment), and some of them are only hypothetical in that we already have them in our basic chord - the lower notes.
That's where the 9 came from, but what about the Bb (the flattened 7th)? That has not been referred to in any way.
Long habit has caused us to believe that when a chord is a 9th it also has the the 7th played flat (which is a Bb in this case) played with it. If the intended chord has no 7th, people tend to write 'no seventh' or 'no 7' next to, over, or under it.
So a more perfect way of naming this strange chord might be C b5 b7 9 - but nobody ever does this. Instead they adopt the strategy of saying something like C b5 9 or C5b9 or C95b (no 7th in any case). This would probably never refer to a chord with the 59th note in the scale added to it! And it would be unlikely to be a Cb chord, which in most cases is better expressed by calling it a B chord.
If your brain is now becoming scrambled with this confusing mess, so is mine but - I am used to it, and I usually manage to work out what people mean when I hear the tune.
Yet more
the major seventh:
Unfortunately this is not the end of the matter, because we need to know more about the 7th.
I can only say that it is long habit that has caused us to name the flattened 7th note in the scale as the seventh when the real seventh is the next note up. In later music than that from which this habit has come a new type of chord has appeared with the actual seventh played, and because it's true name has been hijacked by the flattened seventh people refer to this newer chord as the major seventh. It is still not used as much as the flattened seventh. It's construction is
R+4+3+4 (i.e. Cmaj7 = CEGB)
Major 7th chords get named in numerous ways, including a triangle following the letter name of the chord, +7, M7 (as opposed to m7 for minor 7!), and so on. Try playing one to see what it sounds like.
Now for a final bit of extra confusion. In discussions on the subject of the scale people refer to the flattened seventh as the minor seventh - but they do not refer to the seventh chord as the minor seventh because it is a major chord!
So C minor seventh probably means the interval C to Bb, whilst Cm7 or Cminor7 probably means a chord of CEbGBb!
C chord in key of C = I, and F chord in key of C =IV, so that F7 in key of C = IV7! (and in key of D, say, IV7 would be G7 and V7 would be A7).They can be useful, but take a while to learn for most people.
I think I've confused myself enough for the moment.