Key vs Scale vs Mode: What’s the Difference?

Key vs Scale vs Mode: What are the Differences Between Them?

Some musicians use the terms key and scale interchangeably. This can lead to confusion. When you throw music modes into the discussion, people get downright befuddled. Today I will explain the differences and similarities between the three terms, and when to use each of them accordingly.

What is a Key?

A key is a classification system of notes that sound good together; it’s a way of clarifying what notes are going to be used in a song before you even start playing it. It’s mostly used to write down music for orchestral instruments, but it also has practical purposes for pop and rap music. Knowing the key of a song:

  • Tells you what chords will sound good with it
  • Lets you know if it will clash or harmonize with other songs when you mash them together
  • Allows for easier improvisation of leads or melodic phrases

What is a Scale?

A scale is a series of notes used together in a song. Nearly any combination of notes can make up a scale, but the most common combos are the major and minor scales. The major scale happens to use the same notes as a key, which is why the terms are used somewhat synonymously. For example, the Key of C and the C major scale both imply that the song uses the notes: C, D, E, F, G, A, and B. This is the same for any major scale and it’s major key, as well as any minor scale and it’s minor key.

What is the Difference Between a Key and a Scale

Key and scale indicate the same thing…but only when you are working in a standard major or minor scale. The difference is that keys are meant as written instructions on sheet music about the notes that may be present in a song, whereas scales are implied names for the specific selection of notes that you play in a song.

A key is like a legend at the top of a score that says “heads up: you might see these notes in the following music”, but scales are usually not written down on paper—they are inferred by the specific combination of notes that get played. Furthermore, not all scales correspond to a key and, if a song contains notes not normally in a key, then extra instructions have to be added to the sheet music to clarify that.

For the most part, independent pop producers and songwriters don’t need to know all the guidelines and procedures for writing music scores—that is mostly meant for orchestral music. If you write your songs mainly in a major or minor scale, then using the terms key and scale interchangeably is not a big deal.

Not All Instruments Can Play Every Key!

A notable reason for music keys existing is for musicians who play diatonic instruments. A diatonic instrument is one that cannot play all twelve notes; usually, it’s built to play seven notes in a major scale. Examples include traditional harps, harmonicas, and french horns. Players therefore need to have multiple versions of their diatonic instrument that are each built to play a different scale. Before they even begin playing a song, they need to know which notes are in the song so they can use the right instrument.

But most instruments used in pop music are chromatic instruments, which means they can play any note in any key without needing to be modified or switched out.

What is the difference between a Scale and a Mode?

The last and perhaps most confusing term in this topic is “mode”. Modes are essentially an alternative classification of music scales that dates back to ancient Greece. In the simplest terms, every major scale has seven modes: each mode in a given major scale uses the same notes but starts in a different place (that is, has a different tonal center). This means you are still in the major scale or key, but you are not necessarily using the same tonic.

The main difference between scales and modes is simply their naming conventions. Modes are scales, just organized in a different way. It’s like having two different labeling systems made by two different people: they organize the same information, but not into the same exact categories.

Scales, keys, and modes are all just slightly different ways to group notes together

For example, let’s say you write a song that uses the Key of C Major, but the song starts on F rather than C. The first chord is an F major and the melody resolves to F, but all the notes in the song fit into the Key of C: F, G, A, B, C, D, and E (if it was truly in the Key of F, the song would have a B-flat rather than a B). This means you are operating in a mode of the C major scale: specifically, the name of this mode would be F Lydian. Below is a chart showing every mode for every major scale/key.

The Key to Modes Chart

Ionian (I)Dorian (ii)Phrygian (iii)Lydian (IV)Mixolydian (V)Aeolian (vi)Locrian (VII)
C MajorC IonianD DorianE PhrygianF LydianG MixolydianA AeolianB Locrian
C# MajorC# IonianD# DorianF PhrygianF# LydianG# MixolydianA# AeolianC Locrian
D MajorD IonianE DorianF# PhrygianG LydianA MixolydianB AeolianC# Locrian
Eb MajorEb IonianF DorianG PhrygianAb LydianBb MixolydianC AeolianD Locrian
E MajorE IonianF# DorianG# PhrygianA LydianB MixolydianC# AeolianD# Locrian
F MajorF IonianG DorianA PhrygianBb LydianC MixolydianD AeolianE Locrian
F# MajorF# IonianG# DorianA# PhrygianB LydianC# MixolydianEb AeolianF Locrian
G MajorG IonianA DorianB PhrygianC LydianD MixolydianE AeolianF# Locrian
Ab MajorAb IonianBb DorianC PhrygianDb LydianEb MixolydianF AeolianG Locrian
A MajorA IonianB DorianC# PhrygianD LydianE MixolydianF# AeolianG# Locrian
Bb MajorBb IonianC DorianD PhrygianEb LydianF MixolydianG AeolianA Locrian
B MajorB IonianC# DorianD# PhrygianE LydianF# MixolydianG# AeolianA# Locrian

Take note of a few things here:

  • Each mode has a Roman Numeral next to it’s name. These numerals count which note in the major scale the mode starts on. So if you are in the D Major scale and you start on the fourth (IV) note in the scale, your mode would be G Lydian.
  • The Ionian mode is the same as the basic major scale
  • The Aeolian scale is the same as the relative minor to each major scale (that is, A Aeolian is the same scale as A minor)

Modes are not used much in pop, rap, or rock music; if you’re writing in one of those styles, it’s not really necessary for you to understand modes. They mostly just provide a frame of reference on where the tonal center of the song is (if the tonic you selected is not the major or relative minor of your key).

Summary Table

In summary, here are the main differences between each of the three terms we explored today:

A written system for identifying what notes are in a music scoreA selection of notes played in a song that have a specific pattern of intervals between notesThe ancient Greek version of a scale
15 keys that primarily cover Western music scales (major and minor)500+ possible scales covering any and all style and demographic of music7 modes per key, or 84 modes total in all keys
Used to inform diatonic instrument players what instrument they’ll need; also used by DJs to know what songs will mash up togetherUsed to identify what notes are being played in a song, especially for solo instrumentalists so they can improviseNot used much in modern mainstream music, but work in the same function as a scale

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