Developing and using the fourth finger increases versatility and tonal range and tonal choices. The fourth finger in first position offers a choice between playing an open string D,A or E or playing the same notes on the G, D and A string at the seventh fret. Play an open A then play an A at the seventh fret with the fourth finger on the D string and listen to the difference in the sound. The open A is bright and rings and can even sound harsh. The A played with the fourth finger on the D string is softer and more mellow in tone.
Now play a D major scale from open D string to D 5th fret on the A string using open strings D and A. Now play the same scale without using 4th finger instead of the open strings, in other words starting in D 7th fret on the G string and playing A seventh fret on the D string. What difference do you notice in tone between the two?
As well as the tone choices, when you move out of first position the 4th finger becomes essential. If the fourth finger is week the notes will often sound clipped, muffled or buzzing when the note cannot be sustained or the fourth finger can;t quite stretch to be placed just behind the fret and is landing in the middle or even at the back of the fret.
Here is an exercise I developed from Ranieri’s “L’art de la Mandoline” Book II.
Starting with the A string play open A followed by E at the seventh fret with the fourth finger. Now play B 2nd fret 1st finger followed by E again. Leave the first finger on the 2nd fret and play C# 4th fret 2nd finger followed by E again. Now leaving the first and second fingers in position add the 3rd finger D 5th fret followed by E again 7th fret 4th finger. Now lift the 3rd finger to play C# again followed by E then lift the 2nd finger to play B again followed by E and finally returning to open A followed by E.
It is important while ascending from A to leave each finger in place so the muscles are stretched each time the fourth finger reaches for the E at the the fret. So the sequence is:
A E, B E, C# E, D E, C# E, B E, A E.
Play slowly and evenly using down strokes placing your attention on the 4th finger each time stretching it to play a clean note with a full tone at the 7th fret. Repeat 5 times, take a rest then play the same pattern on each of the other strings. You may notice the G string is more of a challenge.
After practising this sequence for a week change the C# to a C natural 2nd finger 3rd fret. Notice how this is more of a stretch. Again practice this sequence using the same finger pattern 5 times on each string. After a few weeks of daily practice you will notice the 4th finger gaining strength.
If you notice any strain or pain on the back of your left hand stop immediately and rest. Practice for short periods and regularly.