Using your hands to represent how a key works:
Which chords in the sequence are Majors, Minors, and which one is Diminished ?
Hold both of your hands up .
Point your thumbs to the left ( as if to represent capital letters of two sentences )
Close all your fingers then stick up the little finger and the ring finger on each hand.
Think of the left hand as 'The Major Family' and of the right hand as 'The Minor Family.
The thumb of the left hand ( the first or 'tonic' note of the musical scale ) is the 'father' of the Major family.
The ring and little fingers (the 4th and 5th notes ) are 'sons' of the major family ( the sub-dominant and dominant chords respectively)
These are the '1,4,5' chords: a combination which is very commonly used in western folk, blues and other popular music.
Practice saying the musical alphabet from the thumb along to the little fingers to identify which chords occur in the same musical family ( key )
e.g. C d e F G ( if you're playing in the chord of C , the chords of F and G will naturally follow.
If you're playing in the key of E, the chords of ..... and ....... will follow. Try counting through from some other letters.
Now over to your right hand - the Minor Hand.
( Holding it up with your right thumb pointing to the left )
Think of the thumb of the right hand as the 'mother' of the Minor family. ( it is usually known as the 'relative minor' ) it is the 6th chord in the key
Counting through from the thumb on your left hand 1st, 2nd , 3rd, 4th, 5th to the thumb on your right hand , the 6th and on through past the 7th ( the diminished 'leading' chord ) to the 8th ( remember the 8th note is the same as the first so call it the 1st ) and on to the ring and little fingers , the 2nd and 3rd chords in the key: Think of them as the 'daughters' of the minor family ( the supertonic and mediant chords respectively)
The 6th ( your right thumb ) the 2nd ( your right ring finger ) and the 3rd ( your right little finger ) are the minor chords in any key.
They 6th, 2nd and 3rd chords are often played together. e.g. Black magic woman.
1st 2nd 3rd 4th 5th 6th 7th
tonic, supertonic, mediant, subdominant, dominant, submediant, leading note