Major and Minor Keys

Question: This may be very basic, but could give me a broad overview of major and minor keys and scales?

My real question is, for every major there is a minor in the same exact key, so what’s the difference and how can you tell which is which in a piece of music, for instance whether it in C major or A minor? Is there a simple way of looking at the broad spectrum? Thanks so much!

– Barb (Arizona, USA)

Albert’s reply: You’re referring to relative keys. These are keys in different modes (major or minor) that share a common key signature.

For example, C major and A minor have no sharps or flats in their key signature:

Similarly, a key signature of two flats can be either B-flat major or G minor:

So how can we tell whether a piece of music is in a major key or its relative minor when just looking at a piece of music? Most often, we can just look at the first chord, and we can usually simplify even that: usually the bottom note in the first chord is the tonic.

For example, if you see a key signature with no flats or sharps, then you know it must be either C major or A minor. If the bottom note of the first chord is a C, odds are the piece is in C major. Alternatively, if that bottom note is A, the key is probably A minor. Of course, you’ll need to check the remaining notes in the chord to see if you have all of them (C E G for C major and A C E for A minor).

The seventh scale degree (the next-to-last note of the scale) is also usually raised in minor, to form the leading tone. Again using a key signature of no flats or sharps as an example, if you see G-sharps all over the score, the piece is almost certainly in A minor.

Some very interesting exceptions come to mind, but these are very advanced pieces of music. Bach’s first sonata for solo violin is in G minor, which has two flats, but he wrote only one flat in the key signature for the first movement. This Adagio movement is actually in Dorian mode built on G.

Beethoven’s Piano Sonata No. 18 in E-flat major, Op. 31, No. 3 starts on a minor seventh chord built on the second scale degree, but in first inversion, a ii 6/5 chord! If you didn’t understand that… don’t worry, you don’t have to. It’s just a really weird way to start a piece, and Beethoven doesn’t reach E-flat major for several more measures. It’s his way of tricking his listeners!

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