When I was younger, for years, I played musical instruments such as the french horn, violin, acoustic ("standing") bass, electric bass, piano, and electric guitar. During these years, I also learned to read sheet music/music notation.

I've taken many years away from reading music notation, however I still remember quite a lot about it. During the last 3 months, I've gotten into music composition using a software tool called Ableton Live. When I was reading music notation as a musician years ago, I distinctly remember there being what's called a key signature. The way I understood was quite simple: it tells me what notes I need to play either sharp, flat, or natural throughout the song, with the exception of when specific notes were marked as such using what we called accidentals.

As a musician, when I heard "X (song) is in the key of Y", this basically just resulted in me thinking in my head "okay, this means you're going to sharp all Cs, Fs, and As throughout this song unless marked otherwise", for example.

However, as a composer, I'm struggling to understand the actual meaning behind a song that is "in the key of" some pitch. Moreover, I am struggling to determine the keys of my own compositions. In other words, I have actually written melodies and chords in the software that sound good together to me, but without any particular planned key. So, I end up actually having to struggle a bit to determine the key of my own song, so that I can continue to write other music tracks that go well with it, if that makes sense.

So, my question is, what is a better definition, or understanding of what a key actually is, aside from my earlier understanding of "it's some group of notes throughout this song that we are going to sharp or flat?" As a musician, that makes a lot of sense, but as a composer, it's not super useful. In fact, it can be confusing because as a composer, it seeems that "Key" is more suggestive of some note that we continuously return back to, or "resolve" to, but then I have no idea what that has anything to do with the number of sharps or flats.

  • 2
  • 1
    I think the ultimate end goal is that you would have a strong understanding of keys that would serve both playing and writing music in essentially the same way, not that you want to find one understanding of keys for playing and a different one for writing. You want to build on your understanding as a player to help you write, not shift to a different point of view for writing. Aug 28, 2022 at 0:42
  • 1
    When you "struggle...to determine the key of [your] own song", is it because the key is ambiguous/unorthodox (e.g. uses major third scale degree but also b2) or because the key changes too often?
    – Dekkadeci
    Aug 28, 2022 at 6:58
  • 1
    A couple of examples might help. If you’re willing to share a short composition or two? Typical Western music has got a key, some modern compositions have not, so I am curious to see. Also do I understand correctly that what you are after is a key signature (such as one flat before b), not a key (such as F major, D minor, G Dorian, etc.)?
    – Anonymous
    Aug 28, 2022 at 7:35
  • 1
    @Dekkadeci I'd interpret "without any particular planned key" as "I don't have any favorable key signature because I can just transpose the piece to another later/when finished" instead.
    – Andrew T.
    Aug 28, 2022 at 11:14

8 Answers 8


It is possible for a musician to develop facility on an instrument, learn how to read music and play scales in different keys of varying numbers of sharps or flats and even play pieces without really having any knowledge of what a key actually is beyond “this key has these sharp notes”, etc.

In order to understand what a key is from the perspective of your question you must go beyond the sharps and flats and learn about tonal harmony. I will not attempt to give you a crash course on tonal harmony but this information is universally available.

In a nutshell, in tonal harmony the scales from keys are used to construct chords, one for every scale tone. In a major key this will give you 7 chords, one built on every scale tone. In a minor key there are more than 7 chords because of the use of more than one scale in minor keys, the harmonic and melodic minor scales. In both major and minor keys these chords have different functions and tend to be used in recurring patterns in many different styles of music. In any major or minor key the home chord is built on the first note of the scale, C for C major, Ebm for Eb minor, etc. The relationships between the chords of any key are the same, the only difference is the central key note and the actual scale notes the key in question uses to build the chords.

Chord progressions tend to move away from and back to the home chord. Once you learn about the different functions of the different chords which are identified by Roman numerals you will identify numerical chord progressions like I-IV-V with chord progressions you know and have heard many times. This progression for example is used in most blues songs, “Twist and Shout” and “La Bamba” just to name a few. Chord progressions have much to do with how we hear and identify keys. Even a melody with no chords will sometimes imply harmony by the notes selected when composing it.

The one thing to be aware of is that tonal harmony is fundamental knowledge. Nowhere is it written that we must use these principles when composing. There are no rules in music for a composer but more often than not tonal harmony principles are at least partially used. Some pieces may use tonal harmony but change from one key to another and back (and many do). Some may use the basic tonal harmony principles but also incorporate notes and chords that are unrelated to the original key. Some songs may be made up of chords that have no tonal relationship to each other, for example a C major and an Eb minor chord, which have no common notes. In cases like these it might be difficult to actually assign a key. One thing you can do is decide which chord sounds more like “home” to decide.

  • Hmm, this is interesting because I've also worked with some software like "Mixed In Key" which claims to identify the key of a given song. However, since songs can have key changes, I don't quite understand this, maybe it tries to discover what key it believes the majority of the notes are in. Anyway, I will look at tonal harmony further, thanks. I am familiar with the chord progressions and scales as well (though I failed to mention it) but wasn't sure how strong the relationship was between them and key.
    – the_endian
    Aug 27, 2022 at 21:26
  • 3
    @the_endian - The Wikipedia article of "Mixed In Key" implies that all "Mixed In Key" really cares about are the keys of the beginning and the end of the song, as the software seems to be aimed at DJs who would like to pick song orders such that transitions between songs are less jarring.
    – Dekkadeci
    Aug 28, 2022 at 6:54
  • 1
    @the_endian I wouldn’t put much stock in a program that analyzes a song and says: “This song is in D minor.” I’m sure there are times when it is spot on if the music is simple and doesn’t modulate but like I mentioned in my answer there are many underlying factors that determine what key or keys a song is in. It’s better to acquire knowledge and make those determinations on your own. Aug 28, 2022 at 16:55

As a musician, when I heard "X (song) is in the key of Y", this basically just resulted in me thinking in my head "okay, this means you're going to sharp all Cs, Fs, and As throughout this song unless marked otherwise", for example.

That's part of what 'key of Y' means. But not the most important part. THAT is 'Y is the tonic, the home note'.

Other notes will also be used (and they don't have to all be in the 'scale of the key'). The same tonic may last for the whole piece, or different ones may be established in different sections (though we generally return to the original one at the very end).

Key signatures are the least of your worries. Yes, if the key is C major there will be an empty key signature, if it's E major there will be four sharps. Learn to play and write ALL the scales. Dig out a 'cycle of 5ths' diagram if you like, but I'd rather you understood the principle than kept consulting a diagram. There are plenty of Theory #101 textbooks, get one and remind yourself how scales and keys work.


Please don't think differently with your different hats on. The music probably hasn't changed. Key signatures are there to act as a guide, a reminder, as you state.

We regard (as listeners, players and composers) the key of a piece as the place it feels most at home, at rest. It won't always work for all pieces, but the vast majority will have a particular note or chord that feels like the piece could be stopped there and it would be an appropriate end place.

I regard it as real life - we start from the place we call 'home', on the journey, and may visit some or many other places on the way, maybe returning home before getting off again for the next part of the journey. We could go anywhere, stay for a while, or just a fleeting visit somewhere, before moving on. To somewhere else, which may still not be 'home'. But when we arrive at that place we recognise as 'home', we know we're there. That's then the key of the piece, or at least what we decide to call the piece's key.

So, it's a reference point, a datum point, that we as humans tend to need (for many things in life), and that gives us a safe place to regard all others from - just like home should be!

If in a piece you're composing, you find you're needing to sharpen every (or nearly every) F as you go, then probably that sharp sign needs to go in the key signature at the beginning of each line - rather than in front of every F you hear as F♯. For example. That way, you build up the potential key from the evolving key signature.

  • I've seen examples where I and other transcribers all transcribe the same piece, but the number of accidentals in the key signature between my transcription and theirs are different. The last time I saw this, I notated the transcription with a 3-flat key signature (due to the piece being in C minor with Phrygian influences...at least for the most part), but the others notated their transcriptions with 4-flat key signatures (due to the piece using D flat more often than D natural - it still has D naturals in it, though).
    – Dekkadeci
    Aug 28, 2022 at 17:49

The colloquial understanding of music being in a particular major or minor key depends solely on the tonic ("home note") and whether the 3rd scale degree is a major 3rd (for major keys) or a minor 3rd (for minor keys) away. If both the major 3rd and minor 3rd for 3rd scale degrees appear, whether the resulting music is in a major or minor key often depends on genre (e.g. blues would still be in a major key, classical music is labelled with the key, video game boss themes would likely be in a minor key).

By this classification, modes are also categorized into major or minor keys. For example, E Phrygian and F Sharp Dorian are both "minor keys" due to their 3rd scale degree being a minor 3rd away from the tonic, while G Flat Lydian and C Mixolydian (and even D Phrygian Dominant despite this being a mode of the G Harmonic Minor scale) are all "major keys" due to their 3rd scale degree being a major 3rd away from the tonic. In practice, quite a lot of today's music flip-flops between modes that share a tonic (e.g. uses both the regular 2nd scale degree and ♭2), so this categorization of modes into keys is more justifiable.

You can even categorize music that uses all 12 notes of the chromatic scale into a key as long as you know the genre, which note feels like "home" (or at least is used the most often), and which of the 3rd scale degrees a major or minor 3rd away from the tonic is used more often. Note that some music that uses all 12 notes of the chromatic scale is designed to be atonal and therefore be in no key at all.

In classical and ragtime music, and also in pop, folk, and rock music and EDM to a certain extent, knowing the key of an excerpt strongly corresponds to knowing exactly which notes you will consistently be putting accidentals on for all music in that key. Your previous intuition that music being "in a key" means that you sharpen/flatten notes according to the key's key signature is correct for the most part. Major-key music indeed often follows its key signature, while minor-key music notably sharpens its 6th and 7th scale degrees quite often compared to what the key signature indicates. For example, expect to see F♯ and G♯ quite often in music in A minor despite A minor's key signature being blank.

Especially in classical and soundtrack music, music in a certain key is not always notated with that key's key signature. Soundtrack music notated with a blank key signature is commonplace. Classical music (e.g. Bach preludes, Mozart sonata 1st movements) often changes keys without changing the key signature. Trust your ears and the accidentals on the page and in the key signature combined more than the key signature alone when it comes to determining the key of passages of music.

Determining the key of entire pieces gets significantly more complicated due to pieces often changing keys partway through. Music often - but does not always! - begin and end in the same key. While a rule of thumb is that you're often safe declaring a piece of music to be in its initial key, music like Chopin's Ballade No. 1 in G Minor disobeys that rule of thumb (it notably starts in A flat major). You can trust single-movement music that is labelled with its key to actually be in that key, but you cannot trust the key label of any movement after the first movement. For example, the 2nd movement of Beethoven's Symphony No. 5 in C Minor is in A flat major, its 4th movement is in C major, and the 3rd movement of Tchaikovsky's Symphony No. 6 in B Minor "Pathetique" is in G major.

In practice, as a performer who does not improvise live, you don't need to care what key the music you're playing is in as long as you get all the notes right. As a composer, you need to care more about what key your piece is in, at the very least because you're probably notating your music and you want your notation to be understandable. If you're improvising a solo live on a given chord progression, you don't need to care about what key the chord progression is in as long as you stick to the notes of each chord - and if you opt for the chord-scale system when you improvise, you still don't need to care about what key you're soloing in. If you're improvising a cadenza live for a concerto, you need to care about which key you're currently playing in because you need to eventually arrive in the movement's home key. If you're improvising ornaments live for Baroque music, you need to care about which key you're currently playing in, if only to know which neighbour tones of notated but ornamented notes to use in your ornaments.

https://www.berklee.edu/berklee-today/summer-2000/Chord-Tone calls doing this when soloing the "chord-tone method", a more restrictive rival of the chord-scale system.

  • I like your last paragraph - just play the dots in front of you. and it really doesn't matter. But that's o.k. for orchestras and ensembles. For jazz bands, and in my case open mics, it's imperative to know the key in order to support artists who turn up with no charts (often better than those who do, then don't follow them, but that's another story!). So, it will depend a lot on what sort of music is involved.
    – Tim
    Aug 28, 2022 at 16:36
  • @Tim - Oops, I forgot about those who improvise live. I better account for that.
    – Dekkadeci
    Aug 28, 2022 at 17:16

Key means center. "This is in C major" means "this is centered on C major". C major is the center.

As a musician, when I heard "X (song) is in the key of Y", this basically just resulted in me thinking in my head "okay, this means you're going to sharp all Cs, Fs, and As throughout this song unless marked otherwise", for example.

The logic is the other way around. BECAUSE it's in A major, i.e. the notes of the song are centered on A major, it makes sense to have F, C and G be sharp by default. That minimizes the number of accidentals that will probably be needed, assuming that the song follows the style and conventions of traditional Western music. That default is written as a key signature of 3 sharps. We can reasonably make this assumption, since talking about keys and key signatures is something you only do in that context really. There are no keys and key signatures in other kinds of musical contexts except traditional Western music.

Key only means the height of a center pitch, and if the "center chord" which explicates the in-center harmony is a major or minor chord. If you play the same piece one half step higher, in Bb major, then the key signature will have two flats, Bb and Eb. In Bb major, the assumed default set of pitches is Bb - C - D - Eb - F - G - A. But in A major they are A - B - C# - D - E - F# - G#.

Develop a sensitivity for center. Where is the central pitch in your mind? What is the central chord? Which chord makes it feel that the harmony is in balance, not leaning in any direction?

You can move the center of balance. Play the chords F - Bb - C7 - F. Now the center of balance is F major. Then play the chords A - D - E7 - A. Now the center of balance is A major.

Play melodies by ear. Accompany the melodies by ear. Listen to a recording and find out by experimentation where the center pitch and center chord are.

The reason why you have this problem is, you have only been taught to read and pronounce written text, not to listen and say anything of your own. You have not been taught to listen and repeat, only to read out loud. In my opinion, that is a big disgrace.


My advice is:

  • write all your songs in the Key of C

  • transpose your songs from C to G and F

  • transpose your songs from G to Gb and from F to F# and see what is happening and what is different. Play them in G and Gb, in F and F# on a keyboard.

  • transpose your songs from C to D and from D to E.

I think the system of a key will be selfexplaining when playing and transposing a song in F and F#, G and Gb (all notes are sharpened or flattened, the tone material is a halftone up or a semitone down.

Accidentals will be used as alterations leading to the next neigbour tone with a tension up- or downwards.

The best way to develop the keys is to construct the scales in the circle of fifths clockwise up and counterclock-wise down, using the second tetrachord (4 tones of one scale as first tetrachord of the next scale, deriving the new leading tone! (upwards:the 7th (ti) will need a sharp, downwards the new 4th (fa) needs a flat.

  • 1
    In F#/Gb only 6 notes are sharp/flat. To get all 7 notes sharp or flat you'll need C#/Cb. Aug 28, 2022 at 10:14
  • 1
    When a Bb becomes a B it is altered up too - but you're right it has no sharp. And F# becomes F natural, so it needs no flat. Your comment is correct. Aug 28, 2022 at 12:12
  • Oh, you just mean the notes from F are sharp-ened in F#. That makes perfect sense, sorry for misunderstanding. Aug 28, 2022 at 19:06

Your basic understanding of "in a key" is correct. Read the key signature, follow the accidentals to deviate from the key signature.

I suppose you could think of that as the "performance" understanding where you would play whatever accidentals are in the score, because that is what you are supposed to do.

Now that you are considering composition, the question becomes "why?" and "how?" Why and how are accidentals used in scores and how does it relate to the meaning of "being in a key?"

The convention of music in the major/minor key system is to start and end a piece in the same key while in the course of the music unfolding the key may change several times. The key changes are used for tonal variety and to create forward progress in the music. Returning to the key of the beginning to make the conclusion is a way to regain stability.

Stasis, an unchanging state, is inactive, without movement. So, key changes add an element of change, which is active, which equates to movement, even if that "movement" is sort of a metaphor. The flip side of that is sameness, unchanging, no movement, which is rest, which is stable, which ultimately is stopping.

That dynamic of change/unchanging, and its effect on in stability/stability, is a major factor in musical form. Again, a piece will start and end in the same key to first establish the key and then through its eventual return to effect a conclusion. Formally, structurally that give us a beginning, and end. The key changes that take place between can be associated with various formal/structural points and may have various names. In short works a double bar repeat may mark the rough middle of a work, and that point will coincide with aspects of a key change. In larger works like a sonata or fugue the sections have names like "development", "recapitulation", or "episode."

A well rounded musician should understand both of these aspects, the performance part of how to merely read a score and play the correct sharps/flats/naturals, but they should also understand how those things work with key changes and create the structure of compositions. Obviously, a composer needs to have an especially deep knowledge and sensitivity about these things. Rather than two different understandings of "being in a key", it's more like two levels of understanding, one is the merely the "mechanics" of reading notation, the other is the application of keys to form and composition.

It should be understood that this is just an overview of what's conventional, and composers often work against those conventions for effect. Historically the 19th century was when composers started to embrace the unconventional. Eventually that lead to Impressionism, atonality, and lots of modern styles, and the sense of key became expanded or simply abandoned.

  • Pop music also has a form despite staying in the same key for all of the song...or at least much of the song, before the truck driver's gear change near the end that pushes the key up 1-2 semitones and makes the song end in that new key. Very often, both the verses and the chorus will be in the same key.
    – Dekkadeci
    Aug 30, 2022 at 6:56
  • I didn't say other styles don't have form. Other musical elements can be used to created form. In regard to this question an aspect of keys that should be understood is how they are used to create form. Aug 30, 2022 at 12:48
  • That comment of mine was partially to counter your claim that "a piece will start and end in the same key" - even in the turn of the 20th century, American marches and ragtime were rife with music that ended in the subdominant key instead of the home key - along with your implication that no key changes mean stillness instead of musical form in "So, key changes add an element of change...The flip side of that is sameness, unchanging, no movement, which is rest, which is stable, which ultimately is stopping.", and partly to counterbalance your strong emphasis on classical music...
    – Dekkadeci
    Aug 30, 2022 at 15:19
  • ...when the question asker lightly implies that they are not composing classical music ("I played musical instruments such as the...acoustic ("standing") bass, electric bass, piano, and electric guitar", "I've gotten into music composition using a software tool called Ableton Live" - note that Ableton Live is a DAW and not a music notation program).
    – Dekkadeci
    Aug 30, 2022 at 15:21
  • @Dekkadeci, re-read my last paragraph. If the OP gives no style information, then they get back any mix of style contexts. Also, you exaggerate. Regardless of era or style, these conventions hold true for literally countless songs. That is the basis of understanding. Aug 30, 2022 at 15:48

I'm not able to get as deep into the woods as a lot of these baby Bachs but as a guitar playing rocker. I like to play in A minor blues, mostly cause it puts me right at the 5th fret & leaves all the open/cowboy chords there for me to attack. Also I play everything in minor blues cause that's what rock/roll sounds like. I knew that before I knew what a scale was, just from loving rock my whole life.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.