Intervals

Intervals are the building blocks of melody, harmony, and music in general. To understand the music you play, you must at least understand this vital component. This guide is meant to get you started.

Part I - What is an interval?

An interval is created by any two notes. These notes can be played simultaneously or in succession, but in either case are qualified in he same fashion. On the guitar, without the assistance of bending or a tremolo system, notes are bound to intervals built by half-steps as they are in standard music theory. Thus the generalized "for theory" explanation will suit guitar players just fine. I'll be sure to work the guitar playing aspect in as needed.

Before we go any further, make sure you understand the basics of scales (if not read up in the lessons section). To understand the way in which intervals are constructed, it is very helpful, if not necessary, to understand scales.

An interval is decided by the number of scale degrees between the lower note and the upper note. For example, if you were to consider the two notes A and C as part of the A minor scale, C would be the third scale degree, and thus A and C would be considered separated by an interval of a third. An A and an E would be considered a fifth., and so on. If you are accustomed to using standard notation, you can also count the interval as the number of lines and spaces between two given notes (with the line or space on which each note sits included). Below are a few visual representations of this idea.

Part II - Classifying Intervals

So what is the big deal then? Seems simple enough. The catch is that intervals are defined both quantitatively and qualitatively. There are four different types of seconds, thirds, sixths, sevenths, and three types of unisons (when there are two voicings of the same note), fourths, fifths, and octaves (the two of the same note name split by one octave). This stems from the fact that, depending on the scale, any given interval will not sound the same. At this point some of the arbitrary rules of music may start to get on your nerves. Hang in there!

In a major scale, an interval of a third from the root sounds different than the same third scale degree in a minor scale. If that doesn't make any sense, remember that the third note in a major scale is a half-step higher from the root than the same scale degree in a minor scale.

All of the intervals (unison through octave) fall into basically two categories quality-wise. There are the "perfect" intervals (unison, fourth, fifth, and octave), and the "non-perfect" (second, third, sixth, and seventh).

The perfect intervals have three qualitative states: perfect (P), diminished (d), and augmented (A). All of the unisons, fourths, fifths, and octaves found in the major and minor scales are perfect intervals. In other words, the fifth in a minor scale (any of the types listed in the scales lesson) will always be a perfect fifth. A diminished fifth is one half-step smaller than a perfect fifth, and an augmented fifth is one half-step larger. This is how sizes relate among the different types:

The rest have four possible forms: diminished (d), minor (m), major (M), and augmented (A). Think back to the difference between the major and the minor scales. The first third in a major scale is known as (you'd never believe it) a major third. In a minor scale this first third from the root is known as a minor third. They differ by one half-step. However, if you were to contract a minor third by one more half-step, it would be a diminished third. If you were to augment a major third by one half-step it would become an augmented third. Here is another size chart for these intervals:

There is one interval not covered by any of these alterations: an interval of six half-steps (equivalent to an augmented fourth or a diminished fifth) is called a "tritone."

While this may seem arbitrary, it is the only apparent way to make sense of the musical system as conceived. The 1,4,5,8-type intervals are fairly easy to keep track of, and, especially in most pop music, are almost always perfect (as opposed to dim/aug).The other intervals take a bit of memorization, but once you have a good idea of what, for example, a major third and minor third sound like, you can figure the rest out by adding or subtracting half-steps from the intervals you can recognize. While this is potentially confusing at first, and while it will take some rote memorizing, this will all seem really simple in the end. Just remember that alot of these intervals overlap. In other words, an augmented third is the same as a perfect fourth, etc. For more, read up on enharmonics on the lessons page.

Part III - Notation

With any system, especially one that is as seemingly fickle as this one, it is always good to have a standardized way of keeping track of everything. In other words, we want shorthand. This perhaps the easiest part of the lesson. Everything is uniform (thank god).

So here's the deal. An interval is notated as a quality (a single lower or uppercase letter) and a quantity (a number). I slipped you the abbreviations for qualities before, but I can't expect you to remember them, so here they are again in order from smallest to largest.

To make things easier you can remember that Perfect and larger intervals are capitalized, smaller are lower-case. Quantitatively notating is even easier: give a number. If it's a fourth, jot down a 4 and you're done! Thus a perfect fourth would be notated P4, an augmented sixth would be A6, a minor second would be m2 and so on.

Part IV - Inversion

Often times two notes of a certain interval will be played out of order. For instance, in the case of the perfect fifth from A to E, what if you were to play that same E and the A above it rather than the one below? Would it still be a perfect fifth? No. If you were to count ledger lines and spaces in an excerpt of standard notation, you would count a distance of four, not five. This is a very simple example of inversion.

You can read about inversions in greater detail in the inversion lesson, but for now let me give you the gist. Inversion is the simple rotation of the order of a group of notes. With only two notes, you simply flip the order. If it was A then E, it would be E then an A an octave above the original A. The question is, if you have one interval before inversion, what interval are you left with afterwards?

As it turns out, this is one of those times when the inherent math in nature makes things really easy. Here's the deal. An interval and its inversion always add up to nine. Thus a seventh inverted becomes a second, a fourth becomes a fifth, etc. You want to know what an interval will invert to? Subtract its size from nine. Quality-wise things are only slightly more complicated. Remember that table in part III? Quality inverts relative to a horizontal flip of that table. That's really vague, but it will make sense in one second. Trust me. Augmented becomes diminished, major becomes minor, and vice versa. Perfect inverts to perfect. Now does it make sense? No? Well fine then, I'll be blunt:

That should get you started. Now go learn your intervals!