• The Structural And Functional Differences Between The Augmented Fourth And Diminished Fifth Intervals

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    In today’s lesson, I’ll be showing you the structural and functional differences between the augmented fourth and diminished fifth intervals.

    The augmented fourth and diminished fifth intervals have long been associated with the tritone, and in this lesson, you’ll be seeing the differences between these two tritones in terms of their structure and function.

    Attention: If you’re NOT interested in learning how to resolve the tritone, leave this page now!.

    A Contrast Between The Augmented Fourth And Diminished Fifth Intervals

    An interval is the relationship in pitch between two notes in terms of the distance between them.

    Intervals are basically ditonic, meaning that it takes nothing more or less than two notes to produce an interval. The following notes…

    C-E:

    Eb-C:

    …etc., are considered to be intervals because they are formed by the relationship between two notes.

    An interval can either be melodic or harmonic depending on how it is sounded. When the notes of an interval are played together, such an interval is called a harmonic interval, versus melodic intervals where the notes are played separately.

    In this lesson, we’re looking at two related intervals – the augmented fourth and diminished fifth intervals.

    The Augmented Fourth Interval

    It’s important for us to put the perfect fourth interval in perspective before talking about the augmented fourth interval. The perfect fourth interval is formed by the relationship between the first and fourth tones of any major scale.

    In the key of C:

    …where the first and fourth tones are C:

    …and F:

    …respectively, a perfect fourth interval is formed by the relationship between C and F:

    Augmented fourth intervals are larger than perfect fourth intervals by a half step. Therefore, increasing the width of a perfect fourth interval by a half step, produces an augmented fourth interval which literally means ‘a larger fourth interval’.

    Using the perfect fourth interval (C-F):

    …an augmented fourth interval can be formed by raising F:

    …by a half step (to F#):

    …to produce C-F#:

    …which is an augmented fourth interval.

    The augmented fourth interval is also known as the tritone because there are three whole steps within its compass.

    From C to D:

    …is a whole step, D to E:

    …is another whole step, E to F#:

    …is another whole step. The three whole steps within the compass of the augmented fourth interval explains why it is known as the tritone. The earliest augmented fourth interval to be discovered is probably the augmented fourth interval between the natural notes F and B:

    “Check Out The Augmented Fourth Interval In All Twelve Keys…”

    C augmented fourth interval:

    Db augmented fourth interval:

    D augmented fourth interval:

    Eb augmented fourth interval:

    E augmented fourth interval:

    F augmented fourth interval:

    Gb augmented fourth interval:

    G augmented fourth interval:

    Ab augmented fourth interval:

    A augmented fourth interval:

    Bb augmented fourth interval:

    B augmented fourth interval:

    The Diminished Fifth Interval

    Before we also talk about the diminished fifth interval, permit me to talk about the perfect fifth interval. The perfect fifth interval is formed by the relationship between the first and fifth tones of the major scale.

    In the key of C:

    …the first and fifth tones of the scale are C:

    …and G:

    So, the relationship between C and G:

    …produces the perfect fifth interval. A diminished fifth interval is basically formed by shrinking a perfect fifth interval by a half step. So, shrinking C-G:

    …by half step, produces the diminished fifth interval.

    “Here’s how it is done…”

    Using the perfect fifth interval C-G:

    …a diminished interval can be formed by lowering G:

    …by a half step (to Gb):

    So C-Gb:

    …is a diminished fifth interval because it is smaller than the perfect fifth interval C-G:

    …by a half step.

    The earliest diminished fifth interval to be discovered was probably the diminished interval B and F:

    “Check Out The Diminished Fifth Interval In All Twelve Keys…”

    C diminished fifth interval:

    C# diminished fifth interval:

    D diminished fifth interval:

    D# diminished fifth interval:

    E diminished fifth interval:

    F diminished fifth interval:

    F# diminished fifth interval:

    G diminished fifth interval:

    G# diminished fifth interval:

    A diminished fifth interval:

    A# diminished fifth interval:

    B diminished fifth interval:

    Now that we’ve learned the augmented fourth and diminished fifth intervals, let’s go ahead and take a look at their structural and functional differences.

    The Structural And Functional Differences Between The Augmented Fourth And Diminished Fifth Intervals

    The augmented fourth interval is called the tritone, while the diminished fifth interval is called the inverted tritone. The augmented fourth and diminished fifth intervals are basically tritones, hence, they are said to be related.

    There are important structural and functional characteristics that can help you differentiate the tritone from the inverted tritone.

    Structural Differences Between The Augmented Fourth And Diminished Fifth Intervals

    The augmented fourth interval and the diminished fifth interval differ in structure and one notable structural difference they have is in their respective qualities. The augmented fourth interval is an augmented interval while the diminished fifth interval is a diminished interval.

    Another striking difference between the augmented fourth and diminished fifth interval is their quantity or size. The augmented fourth interval is a fourth interval, while the diminished fifth interval is a fifth interval.

    Fifth intervals are bigger than fourth intervals. Although, augmented fourth and diminished fifth intervals are tritones, however they differ structurally in terms of size and sheet musicians understand this better.

    For instance the tritone C-F# (an augmented fourth interval):

    …and the tritone C-Gb (a diminished fifth interval):

    …can be played with the same notes on the piano, however, when written on the staff (for sheet musicians), C-Gb:

    …encompasses five staff positions while C-F#:

    …encompasses four staff positions.

    “Pay Attention…”

    C-Gb:

    …is considered a fifth because it encompasses five letter names:

    C, D, E, F, and G:

    …while C-F#:

    …is a fourth because it encompasses four letter names:

    C, D, E, and F:

    Another set of related tritones like D-G# (an augmented fourth interval):

    …and the D-Ab (a diminished fifth interval):

    …differ from each other in quality and quantity.

    D-G#:

    …is an augmented interval and differs from D-Ab:

    …which is a diminished interval.

    D-G#:

    …is a fourth interval while D-Ab:

    …is a fifth interval.

    Now that we’ve covered the structural differences, let’s proceed to the functional differences between the augmented fourth and the diminished fifth intervals.

    Functional Differences Between The Augmented Fourth And Diminished Fifth Intervals

    Due to the fact that music scholars consider augmented and diminished intervals to be dissonant, diminished fifth and augmented fourth intervals (aka – “tritones”) are all dissonant.

    Tritones are known to sound dissonant, harsh, unpleasant, above all, having the tendency to move to more stable intervals when played.

    The movement of an unstable interval to a more stable interval is known as resolution. The functional differences between the augmented fourth and diminished fifth intervals is basically in their resolution. The augmented fourth and diminished fifth intervals don’t resolve the same way.

    The Resolution Of The Augmented Fourth Interval

    The augmented fourth interval resolves by pushing itself out.

    “Hold On! Let Me Explain What I Mean By That…”

    The augmented fourth interval C-F#:

    …resolves by pushing itself out. In the augmented fourth interval C-F#:

    …the tone F#:

    …resolves by going up by a half step (to G):

    While the tone C:

    …resolves by either going down a half step to B:

    …or a whole step to Bb:

    So the tritone C-F# (which is an augmented fourth):

    …can either resolve by pushing itself out to B-G:

    …or to Bb-G:

    “Don’t Miss The Harmonic Implication…”

    If we add the D bass note:

    …to the tritone C-F#:

    …we’ll be implying a D dominant chord:

    …which will resolve to B-G:

    …with G:

    …on the bass, implying a G major chord:

    In a nutshell, the resolution of the augmented fourth interval implies a 5-1 chord progression in the key of G major.

    Let’s also consider the resolution of the diminished fifth interval.

    The Resolution Of The Diminished Fifth Interval

    The diminished fifth interval resolves by pushing itself in and that’s different from the resolution of the augmented fourth interval.

    The diminished fifth interval C-Gb:

    …resolves by pushing itself in.

    The tone Gb:

    …resolves by going down a half step to F:

    …while the tone C:

    …resolves by going up a half step to Db:

    So the tritone C-Gb:

    …resolves by pushing itself to Db-F:

    In other situations, the tone Gb:

    …can resolve down a whole step to Fb:

    …and when this happens, the tritone C-Gb:

    …would resolve to Db-Fb:

    From the resolution of the tritones, their functional difference is clear and I’m sure you saw that.

    Final Words

    Although the augmented fourth and diminished fifth intervals are all tritones, they differ in function.

    Hence, you shouldn’t be in a haste to resolve a tritone when you come across one. It is of the greatest possible importance to determine whether a tritone is an augmented fourth interval or a diminished fifth interval, because that will give you a clue to its resolution.

    For example, the tritone F-B:


    …is an augmented fourth interval, consequently, it resolves either by pushing itself out to E-C:

    …or to Eb-C:

    In another lesson, I’ll be showing you how to master the resolution of the tritone (whether diminished fifth or augmented fourth interval) in all twelve keys.

    All the best!

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    Hello, I'm Chuku Onyemachi (aka - "Dr. Pokey") - a musicologist, pianist, author, clinician and Nigerian. Inspired by my role model Jermaine Griggs, I started teaching musicians in my neighborhood in April 2005. Today, I'm privileged to work as the head of education, music consultant, and chief content creator with HearandPlay Music Group sharing my wealth of knowledge with hundreds of thousands of musicians across the world.

    Attention: To learn more about this, I recommend our 500+ page course: The "Official Guide To Piano Playing." Click here for more information.




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