A musical interval is the difference between two different notes. Knowing how these intervals appear on the guitar and how to play them is key to progressing with the instrument. Knowing your intervals helps with soloing, finding chords, and more. This lesson goes into simply finding thirds but not really how to use them (that will come later).
If you know about your guitar chords, you’ll know the basis of a chord is made up of the 1, 3, and 5 of the scale (or the 1, b3, and 5 for a minor chord). So if you know your basic guitar chords, you probably also know the 3rd of the chord lies. That’s just a taste of why you should know where to find a 3rd.
What Is A 3rd?
As I’ve already kind of implied, a 3rd is an interval that has a basis of being the gap between the root note and the third degree of a scale. Going further than this, a third is any interval that’s two tones/four semitones (4 frets) apart. A minor 3rd is three semitones (3 frets) apart.
As mentioned, 3rds come in two major flavours: major and minor. There are other 3rds out there, but they’re beyond the scope of this article. When building your typical chord of 1, 3, and 5, the interval between the 1 and the 3 is a 3rd while the interval between the 3 and the 5 is a minor third. If you’re doing a minor chord of 1, b3, 5, the intervals are reversed.
Go ahead and play a major and a minor E chord and listen to the difference in quality. Major chords are generally brighter and happier while minor chords are sadder and more sombre. Because of this, if you’re just playing an interval of a 3rd, it will have similar qualities of the whole chord type.
So now that you know how 3rds are stacked in chords, you can quickly create clusters of them to form chords all over the guitar neck. Sure, you might want to use the fuller sound of a barre chord, but having a nice little stack of 3rds can come in handy for more interesting arrangements.
What Does A 3rd Sound Like?
The first two notes of When The Saints Go Marching In is a major 3rd. The first note (Oh) is the root and the second note note (when) is a major 3rd above that. If you’re trying to hear the interval in your head, just sing When The Saints Go Marching In to yourself.
If you’re looking for a minor 3rd, the first two notes of O Canada are a minor 3rd.
Playing 3rds On The Same String
Sorry to repeat myself, but a major 3rd is two notes 4 semitones/frets apart. So to jump up a major 3rd on the same string, just jump up 4 frets.
Single String Major Third
And, repeating myself again, a minor 3rd is two notes 3 semitones/frets apart.
Single String Minor Third
These intervals work across all the guitar strings since you’re staying on the same string.
Finding Major 3rds Across The Guitar Strings
Finding things across guitar strings is pretty easy. For most of the string, the interval is a perfect 4th, so the 3rd is just moving 1 fret back on the adjacent string. The only difference is the interval between the G and B strings, which is already a 3rd, so you’re using the same fret on the two strings. Standard guitar tuning makes sense once you understand why it’s that way.
The diagram shown has major 3rds across the string all colour coded for your convenience. Everything is laid out in standard tablature format, so the lower string is on the bottom.
Finding Minor 3rds Across The Guitar Strings
The difference between a major and minor 3rd is just one semitone, so to play a minor 3rd, you just need to move your finger back one fret.
Notice how for both the major and minor variations of this interval, the shapes are pretty much the same across the strings (except for between G and B!).
How To Practice 3rds On Guitar
Add these into your practice when you’re practicing your guitar scales. Try playing a 3rd with both notes together (a double stop) or playing the two notes separately when going up and down the scale. Depending on the scale pattern you’re playing, the 3rd will appear in different places, so you can practice making a 3rd on each set of strings!