Scales are essential building blocks of music.  The Preface of Aaron Shearer’s Scale Pattern Studies for the Guitar (1965) begins with:

Before teaching comprehensive scales (up and down the neck), Shearer taught the five fixed-position scale forms. Each scale form is a fingering pattern that begins and ends on a “home note,” or tonic, which also names the key.   The tonic is indicated in the diagrams below as a rectangled” fret on the circled-number string.

Five major Scale forms

For example, Scale form III in Position II has a tonic of D on ⑤ and, therefore, is in D major.  Notice also that the form spans four frets.  Other Scale forms span five frets using a technique called squeeze shift (indicated with arrows).

For more detailed information on scale forms and positions see the articles, Playing in Higher Positions, or Beyond the Open Position

D major

Examples of scale forms abound in music.  Carcassi’s Op. 60, Study No. 9 in A major is a classic example, where segments of 5 scale forms occur within the first 8 measures.

Recognizing scale patterns greatly facilitates reading/learning.  As Shearer explains in Scale Pattern Studies for Guitar:

When learning the fingerboard,  the scale form is a powerful tool for accurately guiding fingers to frets, especially when working in fixed, and harder-to-read positions.  The first task is to memorize the five scale forms and their keys in Position II.  The table to the right lists the major keys available in that position.

Once fingerings are visualized and learned, you can begin transposing them to higher positions to play in other keys.  For example:

• Scale Form I Position II (C major) transposed ⇒ Position IV becomes D major
• Scale Form II Position II (G major) transposed ⇒ Position IV becomes A major

With each new transposition comes new reading challenges and a constant re-ordering of fingerboard notes, but the physical distraction is lessened with a familiar left-hand scale template.

Developing guitarists may be tempted to play the melody in open position, with a slight, awkward left-hand shift between A and G ♯ on ①.  But a more refined solution would be playing in a position where the left hand remains steady, no shifting.

Observe the difference between Open Position and Position II fingerings

It’s clear that Joy to the World is steadier in Position II.  Its note order is similar to open position, with just a few higher notes—B on ③ and E on ①—to learn.

Next, relate our melody to a Scale form in this position.

We can see it matches the upper register of Scale form IV.  

In addition and if desired, Scale forms help when transposing the melody to other keys in other positions.

For example, to play Joy to the World in more difficult-to-read keys, such as B♭or B major, simply move Scale form IV to Positions III or IV as a “road map” for learning any new notes.

The featured duets are in three keys—A, B♭, and B major.  The top melody part is played with Scale form IV and the lower accompaniment played in open or Position I.