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Up until recently I thought that if a song was written in a mode with a major 3rd, then it was in a major key, and if it was in a mode with a minor 3rd, then it was in a minor key. But I read an article that said for a song to be in a minor key, it must have a leading 7th, i.e. one semitone lower than the root note, which none of the minor modes have. So basically, this means that if a song's written in the A Aeolian mode, then it's not actually in A minor, just in the A Aeolian mode. At least that's what the article said.

My question is basically, is this true? If a song is written in a mode with a flat 7th, can you not say that it's in a key?

The reason I thought of this is because of the RHCP song 'Mellowship Slinky in B Major.' People in comment sections are always arguing whether it's actually in B major or not. I know that the bassline uses the B Mixolydian mode, so I always thought that it was in B major, but since it has a flat 7th, is it not in B major?

Edit: here's the link

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Each and every answer has been down marked. Will the downmarkers be brave enough to explain why they think each answer is not good ? – Tim Jun 13 '14 at 9:48
I have commented on both Brad and your answers. I'd be grateful if whoever down voted my answer would do the same. – Fergus Jun 13 '14 at 10:14
I think this is a strange question to ask, therefore I'm upvoting it. :-) From my lack of understanding, I thought that all the modes can be played on a C major (or A minor) key signature? (i.e. no sharps, no flats). So... what's the question again? Is it an apples and oranges thing? – Lee Kowalkowski Jun 13 '14 at 10:57
The guy is saying that Aeolian is a mode rather than a minor key. To most of the Western world it's both. If ABRSM can include the natural minors amongst its scales, surely it can be recognised as a minor key. – Tim Jun 13 '14 at 11:28
@Fergus - we now know what are NOT keys - what's your definition OF a key? – Tim Jun 13 '14 at 18:47
up vote 5 down vote accepted

The basic point that Mr. Ewer makes is correct: a mode is not the same as a key, just as a mode is not the same as a scale. However, he then confuses things by using a different definition of “key” than the one commonly used in modern Western music.

Some minor scales have a major 7th, like the harmonic minor and melodic minor ascending. Other minor scales have a minor 7th, like the natural minor (Aeolian mode), the Dorian, and the Phrygian mode. The only universal feature of minor scales is the minor third, from which all minor scales get their name. Of these many minor scales, we would normally only call the Aeolian, Dorian, and Phrygian scales minor modes, and the natural minor scale is the only that’s the basis of a minor key.

In modern Western music, there are 12* minor keys. Each establishes a specific tonic center with a minor quality. Each has a relative major key starting a minor third higher. These relative keys are also called the Aeolian and Ionian mode, or the natural minor and major scale. While there are many other modes and scales, there are only these 24 common keys.

Mr. Ewer uses a different context for his examples, a harmonic theory where the minor key is a bit different from modern minor keys. I’m not personally familiar with that theory, but it sounds a lot like the modern harmonic minor scale. If you don’t keep that in mind his whole article will be confusing at best.

For a little more context: A big part of establishing a key melodically and harmonically is using tension (dissonance) and release (consonance) to drive the music toward the tonic center. Traditionally, that relies heavily on the V chord and specifically the major 7th (the leading tone). That’s the idea underlying the harmonic and melodic minor scales, and probably what Mr. Ewer is talking about. However, there are other ways of establishing a minor tonic center, such as a blues turnaround or a chromatic descending leading tone (creating a Phrygian feel). These are mainly small alterations to the natural minor scale, which serves as the starting point for the minor key.

To address your question about “Mellowship Slinky in B Major”: The B Mixolydian mode is not the same as the B major key, and you shouldn’t use the two names interchangeably. On the other hand, a bassline with a Mixolydian feel doesn’t necessarily mean that the piece isn’t in B major – Flea could simply be playing with the key a bit for added color.

* Using common key signatures; more are possible with enharmonic spellings.

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Related: – Bradd Szonye Jun 13 '14 at 4:23
I'm aware of that, but that doesn't really answer my question at all... – wumbo Jun 13 '14 at 4:30
Okay, so you're saying that my initial assumption is right, and that if a song is written using A Aeolian then it's in A minor, if it's written using B mixolydian then it's in B major? – wumbo Jun 13 '14 at 4:39
So if it's in B mixolydian, then it's not in B major...? Would you just say it's in the key of B? – wumbo Jun 13 '14 at 4:45
B Mixolydian will never be B major.Only part of each is the same. There will always be a bit of Mixolydian which sounds 'not quite right' if we're expecting the tune to be made up from the scale notes of a pure major. B major key sig. is 5#, B mixolydian needs 4#. For someone to play along or jam, it's important to be aware of the difference.Otherwise, every so often a bum note will appear. – Tim Jun 13 '14 at 7:32

The opening sentence in the linked article states:

""In traditional harmony (i.e., the kind you’d learn in a Classical music school), being in a minor key has a particular definition that gets confused with being in a minor mode.""

He is right. Any good (traditional) theory book will confirm this along with everything else the article states.

The OP's question:

My question is basically, is this true? If a song is written in a mode with a flat 7th, can you not say that it's in a key?

Yes, to both. If the leading tone is not present a key cannot be established.

Modal music cannot establish 'a key' in the traditional sense.

Wikipedia's Aeolian page has examples of songs that employ the Aeolian mode:

Songs that use Aeolian mode
Aeolian mode as a scale is identical with the natural minor scale. Thus, it is ubiquitous in minor-key music. The following is a list of some examples that are distinguishable from ordinary minor tonality.

Bob Dylan - "All Along the Watchtower" R.E.M - "Losing My Religion"

Those song do not establish a key (in the traditional sense). They are Modal songs.

Modal music is widespread in contemporary music (rock, pop etc). Many songs mix modal sections with key based (functional harmony) sections, for example:

the Beatles "Norwegian Wood" spends 16 bars on E mixolydian, then moves to E dorian for 12 bars (Em-A-Em); then the last 4 bars are a ii-V in E major, then to the mixolydian groove.

Many songs have mixolydian verses, going into major key choruses. for example:
Guns and Roses Sweet Child o Mine.
The Rolling Stones Sympathy for the Devil.
The Beatles Hard Days Night.

For simplicity (or ignorance, or brevity) many do not bother to differentiates between a piece with a "key" and a modal piece, they simply state the tonal centre and get on with it, as the RHCP have done.

This has lead to the terms "Key" losing it's more precise definition and to come to also mean "tonal centre of a modal piece" and also "Tonic of a scale" in many circles.

This is fine most of the time but those with formal harmony education such as the author of the article still use "key" as it was defined hundreds of years ago rather than the more vague definition it has gained recently (last 50 years or so).

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"His opening sentence" - Whose opening sentence? I guess it's from the link in the question, but it doesn't become crystal clear when there are other lengthy answers in between. Better to reference it directly. – Meaningful Username Jun 13 '14 at 8:19
Good point, thanks. Fixed for clarity. – Fergus Jun 13 '14 at 8:23
So what I gather is, it's okay to refer to a modal piece as major or minor depending on its 3rd when speaking of contemporary music, but if RHCP were proper music theorists, they would have called it 'Mellowhsip Slinky in B Mixolydian'? – wumbo Jun 13 '14 at 12:08
I think you may be confusing two issues. Whether the 3 or b3 is present is a separate issue to your OP about whether a key is established. eg Phyrgian dominant, lydian, Mixolydian, major pentatonic and Ionian are all major scales or modes, all of them can establish a major tonality but only one can establish a key: Ionian. Saying a song is in B major implies the song is in the key of B major (and not modal). Saying a song is B Mixolydian implies the song is modal (and also tells you it has a major tonality in you are familiar with Mixo). So yes, slinky in B mixolydian is more correct. – Fergus Jun 13 '14 at 13:10
The key (no pun intended) part of my comment was 'when speaking of contemporary music.' I get that it's wrong when talking about classical music, but in contemporary music is it "acceptable" to say the song is in B Major? – wumbo Jun 14 '14 at 1:21

There's some confusion about scales, modes and keys here. Major keys will have a major 3 and minor keys a minor 3. In harmonic, natural and melodic minors, the first 5 notes are the same.Dorian mode also has the same 5 notes. What happens in the remaining two defines which scale/mode is being used. Some songs will stray from one to another, and the classical melodic moves in an unusual way, with the 6 and 7 being 'major' in upward moves, but natural coming down.

The flat 7 or not doesn't in itself distinguish a major or minor key. The 3 does that. It could be argued that a flat 7 actually is an acceptable note with reference to the next part of the tune, as , for instance, in C, a Bb used usually leads to F, which HAS a Bb anyway.

In an earlier question, I stated that there were 3 minor keys, I was wrong - 3 (or more) minor scales, but not keys. Strictly speaking, a mode will probably have the key signature of its parent, as in E Dorian needs 2# as it's the Dorian OF D. That's always a good clue as to what key a piece is in.

In addition, after some more thought, the answer is yes and no. A key is usually thought of as referring to the 'home' note, thus, in F# maj. or min., the pull is towards F#. Otherwise it wouldn't be in F#. HOWEVER, with modes, there is a double pull - there is the set of notes used, which refer to the parent key, call it F# again. To me , at least, a lot of modal stuff still sounds unresolved, say it's G# Dorian, which feels (to me) that only when I hear F# gives finality. But, if it's in G# Dorian, it will end (and probably start) on G#, which certainly establishes its Dorian modality - as G# could be considered as the 'home' note/chord.

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In traditional harmony the key is not simply the tonal centre. to establish a key criteria must be met, not simply establishing of a tonal centre. I understand that many non-classical musicians use key, scale and tonal centre ('home note') interchangeably but in traditional harmony (which the OP's link is about) they have very distinct meanings which makes Brad and your answer wrong. – Fergus Jun 13 '14 at 10:12

There is also certain composers who adhered to a very loose definition of scale. Debussy did this a lot. You would see a piece that you would feel is in E and then suddenly you are confronted with accidentals that make you wonder what exactly is going on.

There is also the fact that modulations occur and they are not always defined to the dominant or relative minor / Major.

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