Learning scales on your guitar fretboard is very essential though some may argue that it is not absolutely necessary. Legends such as Eric Clapton and BB King never learnt scales but the importance of it cannot be denied.

Scales are like the grammar of the language called music. One of the most important scales in music theory is the Major Scale. Most other scales in music is built upon the major scale. The following article teaches you how to learn the Major Scale with a guitar and 30 minutes of your time. 

http://www.songstuff.com/guitar/article/guitar_tutorial_scales/

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