"Reentrant" simply means that the strings do not progress strictly from lowest tone to highest (as on a guitar, fiddle or mandolin), but instead, one or more of the "lower" strings is tuned higher than those which follow, restarting a series, as it were.

An instrument which demonstrates both methods of tuning is the zither. The fretboard strings are tuned serially (non-reentrantly) in fifths, from lowest to highest. The 1st string is tuned in unison to the 2nd, as on the mountain dulcimer, but unison strings are not considered a case of "reentrance" since there's no pitch regression. The harp-like strings are tuned in a reentrant series, with the next string being either a fourth above or a fifth below, the latter occurring when the note would exceed the octave range for that set of twelve strings. The result is a "ragged" tuning sequence. Contrast this with the autoharp, where the strings are uniformly tuned from lowest to highest pitch.

Banjo is reentrant because the 5th string is tuned to the highest, rather than lowest, note. Most ukuleles are tuned reentrantly, with the 4th string tuned a fifth above the 3rd string (though a whole note below the 1st--the 4th string is thus the second highest in pitch).


Why not just say "open/closed" tuning? I can think of three good reasons:

(1) The term "reentrant tuning" is in wide use and has a precise musical meaning. In my reading on banjo and ukulele, I've run across the term repeatedly, and always with the same meaning. If you claim you haven't heard the term, it's probably just because you weren't paying attention.

(2) "Open" is a vague term alreading having too many musical uses. And "open tuning" (as I understand it) refers to a tuning which produces a simple chord when strummed unfretted--quite a different matter.

(3) Why not just say "doohicky" instead of "clef"? Why "sharp", "flat", "chord" or "dominant", for that matter? "Reentrant" is no more outlandish than most other musical terms we accept without complaint.


As for "clawhammering" a ukulele, you certainly can, though not as effectively as on banjo due to the more condensed range of the uke. However, the 4th string, being tuned to the dominant, can easily function as an off-beat drone, in a manner typifying banjo styles.

There is also a melodic benefit to the uke's reentrant tuning: because the 4th and 1st strings are close in pitch, the notes of melodic or chromatic runs can be alternated between the two strings. This allows each note to be sustained longer, for a more legato effect, while the alternation of thumb and finger facilitates speed. It's like the "melodic banjo" style, but requires less jumping about the neck.