What Is a Key?
Understand music's "gravity" to see the flow of progressions
1) Why does knowing the key help you "see" music?
Have you ever listened to a song and felt a sense of "calm" or "resolution" at the end?
That's the "gravity" of the key (tonality) at work.
A key establishes a central note (the tonic) for the song. Every chord and melody moves with a sense of "home," all relating back to this tonic.
Example: In a song in C Major, C is the tonic. When a chord progression flows C→Am→F→G→C, that final C chord provides a feeling of "arrival" or "homecoming."
Understanding this helps you pinpoint the song's center when transcribing or composing.
🎙️ Paul McCartney on Finding "Home Base"
> "When you're writing a song, you need a home base, a key that everything comes back to." > — Paul McCartney (mentioned in multiple interviews)Many Beatles songs feel satisfying despite simple chord progressions.
For example, "Let It Be" is in C Major. It starts on C and returns to C, creating a sense of completion.
While they may have grasped this "home base" intuitively, theory gives it a name: the key (or tonic).
2) The Key = Music's "Gravitational Pull"
Just as Earth has gravity, music has the gravity of a key.
* Tonic (Home): The central note of the song. This is "home base."
* Other Chords/Notes: They move away from and are pulled back towards the tonic.
Understanding this "pull" allows you to:
- Transcribe (Ear Training): Identify, "Where is this song's 'home'?"
- Compose: Fix an ending that doesn't feel "resolved."
- Improvise: Know which notes will sound "finished" and resolved.
3) The 4-Step Method for Finding a Key by Ear
Identifying the key is like finding the blueprint for a song. Use these four steps to dramatically improve your transcription accuracy.
Step 1: Find the "Landing Spot" (The Last Chord)
Theoretical Accuracy: ★★★★★ (Crucial)Most songs end on the key's tonic chord. This provides the listener with a sense of resolution or finality, signaling that the "story" is over and you've arrived "home."
* How-To:
1. Find the very last bass note of the song on your guitar or piano.
2. If that note is a "C," try playing a "C Major" chord and a "C Minor" chord over it.
3. The one that matches the song's final "feeling" or resonance is almost certainly the key. (e.g., if C Major fits, the key is C Major).
Step 2: Check the "Starting Point" (The First Chord)
Theoretical Accuracy: ★★★★☆ (Strong Indicator)Just as stories often start at home, many songs begin on their tonic chord.
* For Confirmation: If Step 1 (the last chord) and Step 2 (the first chord) are the same, you can be over 90% certain that this chord is the key. It clearly defines the structure: "You started at home, went on a journey, and returned home."
Step 3: Feel the "Strongest Pull" (The V→I Cadence)
Theoretical Accuracy: ★★★★★ (The "Pro" Move)This is one of the most powerful techniques. Music has a strong "tension→resolution" dynamic. The most powerful "pull" or "gravity" occurs when moving from the 5th chord (the Dominant, e.g., G) back to the 1st chord (the Tonic, e.g., C). (This is the G→C flow mentioned in section 5).
* How-To: Listen for the moment in the song that feels most "resolved" or "satisfying." This often happens at the end of a chorus or verse. The chord you land on (e.g., the C in a G→C motion) is almost guaranteed to be the tonic (the key).
Step 4: Use the "Melody's Axis" as Final Proof
Theoretical Accuracy: ★★★★☆ (Final Confirmation)If the chords are ambiguous, the melody provides the final clue. A melody is almost always built around the central notes of the key.
* Checkpoints:
* What is the most repeated, prominent note in the melody?
* What note does the singer's phrase "land on" to feel resolved?
* Check if this note matches the tonic you found in Steps 1-3 (e.g., if the key is C, is the melody centered around the note "C"?).
4) Major vs. Minor Keys
Even with the same tonic, the major and minor qualities create vastly different moods.
| Key | Tonic | Atmosphere | Example Song |
|---|---|---|---|
| C Major | C | Bright, secure | "Let It Be" |
| C Minor | C | Melancholy, introspective | Many ballads |
- Major: The final chord sounds "bright" or "open" (e.g., C, G, F).
- Minor: The final chord sounds "darker" or "moody" (e.g., Am, Dm, Em).
However, the same chord can feel different based on the melody or instrumentation, so always trust your ear.
5) Chord Progressions and The Key
Once a key is set, it automatically defines a "family" of chords that fit well together.
Example: In the key of C Major
- C (Tonic - Home)
- Dm, Em (Secondary)
- F, G (Create movement)
- Am (Adds melancholy)
Combining these chords creates a natural-sounding flow.
→ This concept is called "Diatonic Harmony" (covered in another article).
The most important takeaway is that returning to the tonic (C) creates stability.
The move from the 5th chord (G) to the tonic (C)—known as a Dominant→Tonic motion—has the strongest "pull-to-home" feeling.
6) What You Can Do When You Know the Key
Transcribe Faster
If you know "this song is in C Major," you instantly narrow down the possible chords.
You don't have to guess every chord; you can start by checking the "family" of chords that belong to C Major.
Overcome Songwriting Blocks
If you decide "this song is in A Minor," you have a clear direction for your chord choices.
If your ending feels weak, try resolving to the tonic (A Minor).
Improvise Without "Wrong" Notes
Knowing the key tells you which scale to use.
Example: For a song in C Major, you can confidently use the C Major scale (C-D-E-F-G-A-B), and your notes will sound good over any of the chords.
7) Experience It in the App
OtoTheory lets you feel the "gravity" of a key:
- Build progressions: Try starting on the tonic, moving away, and coming back.
- Change keys: Hear how the same progression feels in a different key.
- Match scales: See how the key automatically suggests the right scale to use.
You can finally put a name to the "feeling" you've always heard in music.
8) Summary
- Key = The Tonal Center (Tonic). All other notes are "pulled" back to this "home."
- Find the Key: Check the first/last chord, listen for the strongest "resolution" (like G→C), and confirm with the melody.
- Major vs. Minor: Same tonic, different moods.
- Why it Matters: Knowing the key makes transcription, composition, and improvisation immensely easier.
When you learn to feel this musical "gravity," theory becomes a practical tool.
Next Steps
- To learn about the "family" of chords in a key → What Is Diatonic Harmony?
- To find the right notes for improvisation → What Are Scales?
- To review the basics of chords → What Are Chords?