Partial Barre Chords Basics
Partial barre chords are formed one of two ways: 1) by raising the part of the finger nearest the hand to uncover one or more of the top strings, or 2) by laying the finger flat across the fingerboard but leaving one or more of the lower strings uncovered. The Roman numeral above the partial barre is preceded by a fraction, indicating how many strings are to be barred. Some transcriptions simply use 1⁄2 to indicate any type of partial barre. In some cases the fraction indicates greater detail like 1⁄3 or 2⁄6 (two strings), 3/6 (three strings), 2⁄3 or 4⁄6 (four strings), and 5⁄6 (five strings). The strings to be barred are deduced from the music and tab.
Partial barres make it possible to combine fretted and open strings, providing textural contrast and allowing for some new chord voicings. In Example 3, the open strings give the fretting hand time to make smooth position changes and allow the notes of the arpeggio to flow into each other.
Excerpted from The Alex de Grassi Fingerstyle Guitar Method