The What, When, Why of Guitar Scales & Keys

A lot of guitar players know a number of scale patterns, some will even know what keys that they relate to... But very few guitar players understand what scales are best applied, when they need to be used within a song, and even less will know why they work... So, that's what we're going to cover on this episode of the Guitar Blog Insider...

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90% of the scales we use are from key signatures. Those keys relate to which type of scale we will need to use over a chord progression. Plus, the chords in a progression also relate back to the key signature as well. So, if you study how to tie together the chords, and the scales with how they relate to the overall key signature, you'll have the information that you'll need to play guitar solos, riffs and licks over 90% of the songs you'll ever come across.


Let's begin by taking a look into how this can operate using a common group of chords from one of the "major key" signatures. The progressions "V-Chord" is highlighted in red to identify the stress /pull back to the "I-Chord" (A Major).

Key of "A Major" - Chord Progression (I, III, VI, V, I, IV, V)

When working within a key signature, we need to understand a few details about the key. These will include; the sharps or flats found within it, and how chords move from one to another to create stresses and accents.

Cadence: The way chords move from bar to bar and within a measure to establish an impression of stress and relaxation. When chords become stressed they want to return to a home base. This is referred to as a resolution, in music we call it the "Cadence.".

Even if you don't know a lot about music theory, you'll be able to hear these ideas occur just from listening. In our progression we can clearly tell that the "A Major" chord is our "home" chord.

Perfect Cadence: There is a stress in sound that leads us into each occurrence of the "A" major chord across the measures of our example progression. Something to take note of is how the "A" chord is preceded by the 5th chord of the key, (E). In music we refer to this idea as an "Perfect" cadence.

Plagal Cadence: There is another kind of cadence we need to watch out for. The other popular harmony movement is called a "Plagal Cadence." This Cadence occurs when the "home" chord is preceded by the 4th chord of the key. Listen to our same "A Major" progression, but this time how it functions using a "Plagal" cadence. NOTE: The "IV-Chord" (D Major) is highlighted in red to clearly identify its position.

Key of "A Major" - Chord Progression (I, III, VI, IV, I, II, IV)

As you can tell from the progressions above, chord progressions and key signatures are tied together by how the chords function measure to measure, as well as, how they create stress and then relax that stress through different forms of resolution.

There's another element to all of this, and it's related to the tonality. Sometimes called the "Major or Minor" color of a progression. This is actually very easy to distinguish once you can understand resolution. Because the cadence will point you to the resolution chord, and allow you to hear the "home" chord.

In the progressions thus far, we have been functioning within the Major key. But, the cadence can also work in the direction of establishing Minor key color.

This means if your home (resolution) chord is "Minor" you're dealing with a "Minor Tonality" progression. Let's use the same key signature to create a resolution into the relative minor key of "A Major" ....(F# Minor). NOTE: The stress chords pulling us back to the "F# Minor" as being a home chord are highlighted in red.

F# Minor Progression:Chord Progression (Im, Vm, VI, VII, Im, IVm, Vm)

Notice how the "F# Minor" chord becomes the point of resolution and forms the impression of a "home" chord sound across those chord changes. This is exactly WHAT YOU'RE LISTENING FOR when it comes to understanding what a series of chord changes are doing musically, and how their stress and relaxation influence the next step.

The next step involves what scale you need to consider for performing a melodic line. As you could tell from the chord progressions, we have colors of both Major and Minor.

Those colors also tell us whether we need to play the major or minor scales over our progression. One of the easiest ways to select those sounds is through the Major and Minor Pentatonic scales.

Let's use that first key of "A Major" progression and create an "A Major" melody line, using the "A Major" Pentatonic scale.

 A Major: Major Pentatonic Melody

The Pentatonic scale is fantastic for creating melody lines over progressions because it has such a natural lean toward melody. The scale has no 1/2 steps making it very similar to an arpeggio and this gives it the ability for its group of notes to produce melody.

Now, just as with the Major Pentatonic being a fantastic way to create melody over Major keys, the Minor Pentatonic is also excellent for producing melody over minor situations. In the next example. we'll use "F# Minor" Pentatonic to create a melody over that "F# Minor" chord progression.

F# Minor: Minor Pentatonic Melody

The application of the Pentatonic scale for our melodic ideas (once again) works so nicely here in the minor key, because it uses notes that are closely related to the arpeggios, (which offers us an excellent way to connect to the chord tones. This "chord tone connection" means that from the information we've covered here, you can become even more aware of the value in understanding key signatures.

The information covered will not only help you better understand chord tone connections, they will also help you notice how chords from the key relate to the color of the tonality (through the use of cadence points).

When it comes to starting into the world of playing solos, the strength that exists from using the Major or Minor Pentatonic as a starter scale for creating melody will be extremely helpful. After getting used to playing melody lines with the Pentatonic Scales, you can begin going even further with these ideas by using other scales and modes.

All of this information works in the same way, regardless of the key, the musical style, or the notes involved. And, while Jazz and Classical harmony can become slightly more complex in its nature (of how these ideas are applied), the principles are all still the same across every style of music.

I'd like to end the lesson by saying, thanks for joining me... If you want to learn more about what I do as an online guitar teacher, then head over to my website at and sign up your FREE lifetime membership.

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I'd also be interested to hear your thoughts on all of this in the comment section below. If you enjoyed this video, please give it a thumbs up and subscribe for more on YouTube. Thanks again and we'll catch up next time, for another episode of the, "Guitar Blog Insider."



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