Yesterday in Larry’s interview yesterday he mentioned the fourth finger approach. Sor and other guitarists from the 19th century used this approach to fingering, as did earlier composers–perhaps as far back as Milan.
Most guitar methods begin with single melody line material. The logical choice seems to be using 1 finger per fret. So as beginners learn the 1st and 2nd strings they use the first finger for the first fret and the third for the third fret.
However, as the music becomes more difficult and bass notes are added, it becomes easier to use a bit more externally rotated hand position (pinky side of the knuckles further away) and use the fourth finger at the third fret. What’s really interesting is that many methods actually switch to the fourth finger approach at some point. The Parkening method does this: he fingers everything at the third fret with the third finger. Then around page 40 when fretted bass notes are added he switches to the fourth finger.
This is not a huge deal for adult students. It is a big deal for young students–suddenly altering approaches to fingering can be confusing. The result is often that the habit of using the third finger carries over and the student has a lot of difficulty making the switch.
The fourth finger approach can really be boiled down to this: use the four fingers on the left hand in the span of three frets rather than four. To that end, it can really be used anywhere on the neck. It’s especially useful in situations like I mentioned above: bass note with 2, melody note with 4. In addition to that specific situation, many chord shapes utilize the approach.
It’s worth it to consider this method of fingering when learning a new piece. It makes a guitarists life much easier. Examples can be seen in many new methods. Stanley Yates graded repertoire books and his method both utilize the fourth finger approach. As do Scott Tennants Pumping Nylon repertoire books.