The 4th, 5th and 6th strings are picked with the thumb (P). In almost all cases a free stroke is used. After striking a string the thumb should move over the third string and return to its original position ready to strike again. Your thumb should feel as if it is moving in small circles. Once again consider the two options for the position of the right hand thumb.
The classical position: The wrist is arched, thumb 45 degrees to the string and the thumbnail is used to pick the string.
The contemporary position: The wrist is kept close to the guitar face, the thumb almost parallel to the strings and the side of the thumb is used to strike the string.
On the following recording the classical position is used on the 1st time through, the contemporary position on repeat to highlight the difference in sound when using the nail of the side of the thumb.
The next example is typical of the type of right hand thumb movement that will feature in the early stages of this book. This exercise requires the 2nd finger of the left hand to fret the 2nd fret of the fourth string (an E note).