This is a short introduction to music theory useful to jazz, rock, pop musicians on any instrument or voice - and helpful if you compose or improvise music. Although we'll be looking at the piano keyboard, most of this approach works equally well on guitar or bass. My other hubs on piano chords have photos of the chords if you are more of a visual learner. For me, it's been much easier to learn piano through patterns and memorizing chord shapes, and I actually find reading music fairly unpleasant.
I have bought loads of music theory books - some of them are great, but it's so hard to stay focused on the material, which gets close to maths a lot of the time. Classical theory will make you lose the will to live. Should you wish to pursue this, it's easy to find on the internet - but all you really need to know is harmonised scales and the cycle of fifths in my opinion. Certainly, that is the practical and relevant stuff.
If you play guitar or bass, I would strongly advise you to get some basic keyboard knowledge. It can be very easy to transfer guitar and keyboard ideas from one instrument to another, and the underlying theory is easier to see on keyboard.
Guitarists and bass players will probably gain a lot from seeing how chord inversions work, which is much easier on the piano. For instance, a D chord (consisting of D,F# and A) can sound a lot better with an F# bass note underneath, or an A bass note.
Chords and harmony
If you look at some songs from a Beatles songbook, or at chordie.com for example, you will see the same combinations of chords are used again and again, because they fit well together and support the melody in a logical/ predictable manner. Even if you go back to the 1930s, much of the material is what we're using today, and was used by the greats of modern pop music throughout the 1960s and 1970s.
A key, or tonal centre, is usually established by the first and last chord of a song. So if the key is C (first and last chord will usually be a C) you can use these notes: C D E F G A B C
with these chords:Cmaj7, Dm7, Em7, Fmaj7, G7, Am7, Bm7b5. Cmaj7.
Each chord is built on a note of the major scale. You could use just plain major and minor chords, but these sound more inspiring. For reference: Cmaj7 contains the notes C, E, G, B. To play this chord on piano it's play one, miss one on the white notes only. All the other chords are the same pattern, moving up one step at a time, to your right. If this needs more explanation, please check out my other hubs. When you can play this sequence in your right hand, add a bass note with your left, one octave down. An octave is eight notes.
Using the chords - I'd recommend just using any three chords together, ending on a C chord. For instance, Dm7 G7 Cmaj7- which is a strong sequence. In your left hand add the bass note of the chord.
If you number each chord with Roman numerals - chords I, IV, V would be C, F, G7. These chords are the building blocks of all those songs from the 1950s and the early days of rock n'roll, often extended to C Am F G7 sequences. Still all you need to write simple songs, especially if you fit them into regular 8-bar patterns.
Improvise over the top with C D E F G A B C, or even easier, a pentatonic scale like A C D E G A. Then try cautiously adding some of the other chords now and then.
Using different keys
Now the good news - the intervals between all the notes and chords, or the distances between them, are just the same for all the other keys - they just start at a different pitch. So in the key of D we find:
Dmaj7, Em7, F#m7, Gmaj7, A7, Bm7, C#m7b5, Dmaj7
and the major scale is D E F# G A B C# D. Everything is the same, but moved up 2 frets or 2 notes on the piano
More handy stuff
The cycle of fifths contains a lot of essential information. Look up my hub Music theory- The Cycle of Fifths.
Looking at C for example, the adjacent points are F and G, giving you the I, IV, V chords in any key. The very common ii V I sequence is found by going anti-clockwise, three steps. In every key the ii chord is minor, the V chord is a 7th, the I chord is major. In this key Dm7, G7, C. All other keys work the same way. In jazz, a common progression is a minor ii V I or Dm7b5, G7, Cm7 which you can transfer to all other keys in the same way. In another key it would be using E, A, D to give you the chords Em7b5, A7, Dm7. Again, you are going three steps around the circle. Four-step sequences are also very common, and sound great. For instance, Am, D7, Gmaj7, Cmaj7.
Do I need the whole cycle? Not really. Up to 4 flats and 4 sharps will do. This is as far as E in one direction and Ab in the other.
My new hub Guitar- advanced and jazz contains chord pictures and a lot more info on applications of this.
Another recommended hub is by nvsongwriter on the nashville number system.
Doing your homework
If you find any of this info useful or interesting, check out Tom Kolb's book on theory on the link below. It's very good value, and well written. Although guitar-centric I think many keyboard players would welcome the clear and practical approach. It includes a CD, which is a real bonus.
Naming the notes
On any instrument the note names follow the same sequence:
C C# D D# E F F# G G# A A# B (with sharp names)
C Db D Eb E F Gb G Ab A Bb B (flat names)
So F# and Gb are the same notes. Depending on the key signature you call them one thing or the other. Classical musicians might know this as "enharmonic equivalence" - let's just call them "the same bleedin notes".
Guitar players would learn this sequence starting on the E as strings 1 and 6 are tuned to E, it makes it all easier. Just remember there is no extra note between E. F and B, C. All the others have them. On piano, this is easy to see because there is no black note between the two notes.
If you play the sequence of notes above, you are playing what is called the Chromatic scale. In the real world, you'd only use short sections of this, because it doesn't sound that great. A chromatic run of C, B, Bb, A for example is really common in jazz from the 1920s-1940s.
In some of my other hubs this is discussed in detail. Very briefly:
A C chord is c,e,g (play one, miss one on the piano keyboard) Normally the C or tonic note of the chord is at the bottom, the lowest note in the chord - but you can use any of the three notes as the bass note, giving you inversions of the chord. Try playing the same chord over an E bass or G bass note and it can make the chord progression sound much better.
Play C, C/E (C over an E bass note) F - a bit like the Penny Lane chorus!
Some of The Kinks songs as well as those by the Beach Boys make great use of this idea.