I was graciously granted permission by virtuoso and educator sans pareil Philip Hii to reproduce here his article 'An efficient free-stroke'. This article and many more can be found on his site.
" September 5th, 2017
An efficient free-stroke must incorporate several essential properties.
First, it must have a built-in rebound mechanism. Meaning that the stroke must not only pluck the string efficiently, but also has a mechanism to return it to plucking position again.
Second, it must occur in a continuous flow of action—the movement of the finger to the string, the plucking action and the rebound should all occur in one motion.
And if you have a series of notes (plucking actions) there should be no stops and starts between the actions. The series of notes should occur in one continuous motion.
Third, it must have a built-in tension-release mechanism.
All actions produce tension. This tension must be released dynamically as you perform the actions (otherwise it will accumulate and you will choke with all that tension).
Fourth, it must not impact the other fingers. In other words, minimal sympathetic motion between fingers.
Fifth, it must move with extreme economy. There must be no wasted motion. The purpose of the stroke is to pluck the string, nothing more. There must be minimal follow-through of the finger after plucking.
So how do you produce a stroke that incorporates these properties?
I’ve found that the key is the vertical stroke.
(Relatively speaking of course—vertical to the soundboard and relatively vertical compared to more traditional plucking methods.)
Most people think of the plucking motion as a horizontal stroke. The finger pushes through the string in a motion that is horizontal to the soundboard.
With the vertical stroke, the finger actually pushes into the string slightly before plucking it.
To achieve this, you’ll have to focus your plucking at your fingertips.
By plucking with your fingertips, you’ll have automatic economy in your movements. The movements will be so small, you’ll feel as if you’re not even moving at all.
The actual sensation of plucking is that of brushing upward across the string as opposed to plucking it directly.
Playing with the fingertips takes care of the fifth property, that of economy.
Next, the actual plucking motion must be the moment of release.
This is important. Think of letting loose an arrow from a bow. That’s the kind of release, a complete letting go of the tension at the fingertip.
This takes care of the third property, the dynamic release of tension.
With this stroke, the instant you pluck is also the beginning of the action to reposition your finger.
Think of the plucking action as a movement to reposition the finger. As soon as you pluck, your finger is already traveling back to playing position.
This takes care of the first property—the built-in rebound mechanism.
When we pluck, we’re essentially moving the fingertip from one point (the beginning point) to another point (the ending point).
How do you move back and forth between two points without stopping and starting every time we change direction?
By moving in circular or oval shaped trajectories.
Circular motion produces the continuous looping actions required in the second property.
When you push into the string, the release is upward rather than inward (into the palm).
This automatically produces the oval trajectory that you see in many good players. With this stroke, you don’t have to worry about trying to produce the oval trajectory. It’s built into the stroke.
Finally, the vertical stroke reduces sympathetic motion in the other fingers.
You can try it. Move one finger inward as if you’re closing a fist. You’ll find that the other fingers will want to move inward too. This is sympathetic motion.
But if you move your finger downward and upward (relatively speaking), you’ll find the sympathetic motion is minimal.
An additional note about these descriptions.
Firstly, the upward motion is not to be confused with the hooking up motion that some beginning players do. Your plucking motion should still be pushing through the string to pluck it, but as soon as the string is plucked, the fingertip relaxes and moves upwards.
Secondly, (and I’m aware I’m repeating myself here) the words vertical and horizontal are meant to be taken relatively. They refer to the plane of the soundboard and are not meant literally.
Vertical is not meant to be straight up and down.
It’s only the feeling of moving the fingers vertically. In actuality, the finger is still moving across the string to pluck it, but the sensation is that of pushing into the string vertically and releasing vertically."