When you play a chord, say C (holding down the notes of C, E and G). you would typically hold the major position, so the bass that sounds is your left-most and smallest finger of your left hand. That’s playing the root bass of C on the C chord.

In a song arrangement that requires you to hold the chord longer, you don’t have to just keep pressing the C bass for your C chord; as doing so would sound boring and monotonous.

Instead, you should try alternating C bass with a second bass of G. This sounds right, and is allowed because G is one of the notes making up the cord of C.

So, just keep in mind that every chord has at least a second bass you can play on (if the time allows), and that 2^nd bass is always 5 semitones to the left (lower) , or 7 semitones to the right (higher), of the root bass.

You can figure out the 2^nd bass of any chord by counting either of the above ways. Hence, the 2^nd bass of F chord is C; for Ab it’s Eb; for G, it’s D etc.

To illustrate further in the diagram below - after your left hand holds the the notes in the first diagram, your little left finger then plays on the lower G bass note, and then goes back to the C normal position. You can also play the higher bass (ie., the G to the right of C) in the second picture to add variation, but it usually sounds better playing the lower G bass (to the left).

Now, it would also be ok if you make E (being one of the 3 notes making up the C chord) the second bass after playing C, but it just doesn’t – generally speaking - sound as nice as the ‘further-away G. Playing E would be more approriate right if the song arrangement requires you to play the chord of C in the 2^nd inversion position… ie. a chord made of E, G and C).

Playing C and its second bass of G applies to pretty well all the old-style tempos like swing, march, rock, tango, waltz, and also the latin beats. You can turn on an auto chord accompaniment on an electronic piano, and hear exactly what I mean; because these pairs of basses will sound for most of the rhythm variations, when you press any chord.

Thank you.