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Can I Count Semitones (half steps) to Work out Musical Intervals?

Short answer: No.

About once every few months or so I get an email from someone who has counted the semitones between two notes and arrived at an interval which isn’t the correct one.

They write either to ask me to explain why they’re wrong, or, less often, to complain that I’m wrong :o)

This is the type of thing that tends to cause confusion:

Augmented 5th

If you count the semitones above D (D#-E-F-F#-G-G#-A-A#) you will find there are 8. 

Now let’s compare this interval:

Minor 6th

Counting the semitones here produces the exact same number: 8 semitones (D#-E-F-F#-G-G#-A-Bb)

Some people will argue that these two intervals must be the same, because they have the same number of semitones, and they also seem to sound the same (use the media player buttons to check this for yourself).

But they use different notes, and they are in fact different intervals.

▶ D-A# is an augmented 5th, while D-Bb is a minor 6th.

For this reason, counting intervals is not considered a good method for working out intervals. But this isn’t the only reason why – there’s a more important reason, which I’ll explain below.

And in fact, the truth of the matter is that these two intervals might seem to sound the same, but actually, when you hear them within a piece of music, they don’t sound the same at all. How can this be? Read on!

The intervals that are called “major” and “minor” are the “softest” sounding intervals to our ears. They sound pleasant and gentle. When you press the “play” button at the top of the page, you are most likely hearing a minor 6th (D-Bb), and not an augmented 5th in both cases, because our brains tend to latch on to major and minor intervals more easily than augmented or diminished ones.

Written as a minor 6th, D-Bb is an interval found within the key of Bb major (and other keys). So to be sure that we are hearing a minor 6th, we first need to firmly establish a specific key in our minds. We can do this quickly by playing a Bb major scale, and tonic triad. Here’s the Bb major scale, tonic chord, and then the interval of D-Bb. Listen carefully to the interval, and think about whether it sounds soft, or jarring.

B major scale, key chord and minor 6th

The note A# doesn’t occur in key of Bb major, but it does exist in the key of B minor. So, let’s change the key to B minor. To establish the B minor key, listen first to the scale and tonic chord in B minor. You’ll then hear D-A#.

B minor scale, key chord and augmented 5th

You may be surprised to find that it now sounds completely different! You may even be thinking this is some kind of trick – please use the play buttons at the top of the page to prove there is no trickery involved! D-A# does not sound like D-Bb.

Counting Semitones is Unmusical  

When it comes to theory exams, you need to get the answer right to get the mark – this much is, hopefully, obvious. If you describe an augmented 5th as a minor 6th, you’ll get it wrong.

But equally, if not more important, is the fact that counting semitones also prevents you from really understanding what intervals are about. 

  1. The number of semitones in an interval is simply that – a number. If you know this but don’t know what the interval sounds like, it’s a bit like knowing that a square is made up of 4 x 90° angles, but without being able to draw one, or recognise one in a picture. It’s obvious that the most important bit of information about a square (for most people) is what it looks like. The most important bit of information about an interval is what it sounds like.
  2. If you need to sightread music, this task is much easier if you can imagine the sound of the music just by looking at it. You can only do this if you know what the intervals between the notes sound like. This is especially true for singers.
  3. We describe intervals in words so that we can talk about them with other people, and they can imagine the precise sound we mean. If I tell you that in Bernstein’s song “Maria” the word “Maria” is sung to an augmented 4th followed by a minor 2nd, you will know exactly how it goes, even if you have never heard it, or seen the sheet music. And it doesn’t matter what key it’s in – it’s an augmented 4th whether it’s in C major, F major, or anything else.
  4. Any piece of writing which analyses music will refer to intervals by their name, not by the number of semitones in it. Writing about an “augmented 5th” conjures up a jarring, dissonant interval in the reader’s mind. Talking about “8 semitones” does nothing of the kind, because it might be a minor 6th!
  5. On a deeper level, if you know, for example, that augmented 4ths are quite hard to sing, and that for thousands of years they were avoided by composers completely, you will open up a vast and fascinating insight into music theory history.