Fool-proof way of telling the key based on the key signature (major vs parallel minor)?

Question

Let's say a key signature has one flat, B flat. It could obviously be F major, but it could also be in its relative minor, D minor. I already realize you could tell the difference with the tonic, what chords it uses, etc. but none of those methods are foolproof.

So is there any way one can be absolutely, 100% certain a piece is in the major key rather than the minor key?

ETA: I understand there are similar questions already asked, but there has been no satisfactory answer (they were either too specific or no answer was given).

Answer 1

The tonic of a given key is the note/chord which feels most 'at home'. The place where the piece is at rest, or could stop at that point, and no-one would feel it had to continue to be completed.

As ggcg states, minor keys usually have more accidentals, particularly the leading note, which doesn't show in the key signature, so needs taking up a semitone. Key sig. of Dm is B♭ - we don't put C♯ there as well, even though it gets used frequently in Dm!

Music being what it is, it makes its journey through relative major and minor keys when it feels like,(simple modulation), so sometimes there's no convincing proof as to which key it's in. 'Fly me to the Moon' starts on A minor, but ends on relative major,(C), so what key do we put it into? So, whilst there is a possibility with a lot of pieces, it's not an absolute.

Answer 2

In the realm of 1950s ABRSM theory exams, we were taught to spot the sharpened 7th note (which would be notated as an accidental) as the invariable clue that it was a minor key. The harmonic minor scale was seen as the 'normal' version. Melodic minor was a slightly disreputable alternative, Natural minor wasn't even mentioned. We were also warned to look out for the 'tierce de Picardie' where a minor key piece might be given a major final chord.

Real-life music, even in 1950, was more complicated of course! Even simple tonal pieces might move freely between major and minor. Sometimes there's no right answer to 'is this piece in C major or A minor'. I'm afraid your urge towards neat classification may have to go unfulfilled.

Answer 3

Actually if the tune is in the relative minor key it will likely have more accidentals as it would use harmonic or melodic minor, e.g. modes with a raised 7th (leading tone) and possibly raised 6th. The major key would not typically employ these notes.

This is not a guarantee as many modern songs in minor keys use natural minor. How you can tell is based on the structure of the melody. The melodic themes would emphasize the {1, b3, and 5, possibly b7} of the rel minor scale on strong beats. In other words if melodic ideas gravitate to notes of the vii chord or begin and/or end on the vii then it will have that minor sound and feel.

However, there are exceptions. The fact is that one can take a song completely in a Major key and via chord subs harmonize it in the relative minor (and vice verse) and it will work! It will sound good. In such cases the key may be ambiguous. There are lots of ways to play this trick on the ear so in a sense there may be no foolproof method.

Also keep in mind it is not uncommon for songs to change key so one cane modulate between X major and its relative minor.

Answer 4

Is there any way one can be absolutely, 100% certain a piece is in the major key rather than the minor key?

In general, no. Perception of tonality is subjective, and saying that a piece is in a given key isn't an objective statement of fact about the piece - it's more like an invitation to hear the piece from that perspective.

You can imagine cases where it would be very hard to argue that a piece was in D minor rather than F major - for example, if there was never a D minor chord or an D note played! but even then, someone might still consider the piece to be in some other mode of F major.

I guess if the composer has written "F major" on the score, that might give you an 'official' answer in some cases...

Answer 5

You are talking about a piece of music - not only a short motif (like the beginning of Beethovens' fifth symphony) ...

I pretend that it is absolutely certain to derive this from the sharps (leading tone) or melodic lines or a second voice and especially from the "home tone" which is usually the finalis - except the piece "modulates" to the dominant like BWV 999 or ends in a chord with a major third (called Phrygian ending).

If you doubt about this you should give an example where you mean that there is an ambivalence.