One of the videos I watched on MandoLessons talked about how to play scales using something called “four finger closed position.”
Four finger closed position or FFcP is a fingering pattern that allows you to play any scale. My music theory understanding is incomplete, but as I understand it, this pattern works on the mandolin for two reasons. One, the strings are tuned a 5th apart from each other, and two, it is played diatonically. That is to say, each fret is one half step higher than the preceding one.
If you put your first finger (your fore finger) on the 7th fret on the G-string you’ll play a D. If you skip a fret and place your second finger on the 9th fret you’ll sound an E. Skipping a fret again, putting your third finger on the 11th fret plays an F#. Placing the pinkie or 4th finger on the 12th fret plays a G (one octave higher than the open G string itself). This finger pattern duplicates the whole step - whole step - half step at the beginning of a major scale.
The second half of a major scale also follows the whole step - whole step - half step pattern. The first note of the second half of the scale is a whole step higher than the 4th note of the first half. Which makes the major scale pattern look like this:
whole - whole - half - whole - whole - whole - half
In the case of a D major scale the names for these scale degrees are
D - E - F# - G - A - B - C# - D
After playing the first 4 scale degrees: G (fret 7) - A (fret 9) - B (fret 11) - C (fret 12), you move your hand over one string to the D-string, and play on the same 4 frets. Since the strings are a 5th apart, the D-string 7th fret is a 5th higher than the 7th fret G-string note, or an A. Skipping up to the 9th fret nets a B. The 11th fret sounds as a C#. And finally we reach the 8th scale degree, D, on the 12 fret.
The whole pattern looks like this:
fret: 7 - 9 - 11 - 12 **G-string**: D - E - F# - G **D-String**: A - B - C# - D
This pattern can be started on any fret, on any of the G, D, or A strings, and it will result in a major scale. This pattern also works on the cello, violin, and viola. You leave behind the relative safety of open strings, but it nicely unlocks the relationship between neighboring strings that are tuned a fifth apart.
On my cello, which is played chromactically rather than diatonically, the stretch between your fingers as you play whole - whole - half requires that you move your hand - particularly in the lower positions. Even so, it opened up my grasp of how the scale degrees on neighboring strings relate to each other.