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I'm on the first chapter. From what I understand, given an interval of a 4th, the topmost note is the tonic of the interval. In the attached image, the whole note represents the tonic of the interval. I don't understand why for the C Lydian Scale, the F# is not the tonic?

lydian scale vs major scale

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Short answer: in the case of C-F# both can be thought of as tonics, because the interval is symmetrical. The figure you quote shows that each sound of the scale CAN be interpreted as having tonic C, not MUST. Note that it's impossible to do the same for C-F, their only possible relation is with F as the tonic (in Russel's theory, of course).

Long answer: "pure" tonic is only defined for an interval of a perfect fifth. There is also a transitive dependency between tonics: when you have G (we mean the "pitch class", not a single pitch), then it's tonic would be C. But then C's tonic would in turn be F and its tonic in turn would be B flat. The implied rule is that you are not allowed to make more than 6 such jumps in a row, because by the 6th jump you already have a full scale.

So, if you have two sounds from the same scale and want to see which one is the tonic, you need to see which one is reachable from the other in 6 or less perfect fifth jumps down. When you try C and F you will see that the only possible way is to start with C and make a single jump down (you would need 11 jumps down from F to C). This makes F the tonic. With F# and C, you can begin with F# and you will reach C after 6 jumps. Or you can begin with C, and you can reach F# in exactly the same number of steps.

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Intervals are always calculated from the lower note.So if an interval has C ♮ as its lower note, so e it. The interval is worked out from C>F♯.

It doesn't matter a jot if 'C Lydian' is involved. If someone is calling it 'C Lydian' (mode), then the root will be C. It certainly is the lower note. F♯ is the other note - certainly not the root or tonic. No sense there! Either you've quoted incorrectly, or the site (like too many others) contains someone's lacking knowledge. Where's it from?

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  • Well, if you hear a perfect fourth, the upper note can be perceived as the "root". Right? Like in Smoke on the Water, if you play the guitar riff only without bass, I guess nobody would think that the lower note is the bass? I mean, hearing it as "sus4" needs more imagination. But for the C - F# tritone ... different situation. – piiperi Reinstate Monica Apr 4 '20 at 20:43
  • @piiperiReinstateMonica: No. There's nothing in a perfect four that suggests that the upper note is a "root", whatever that would mean. – fdreger Apr 4 '20 at 22:30
  • @fdreger Did you look at a perfect fourth under a microscope or did you listen to it? Or did you read it in a theory book, or where's that statement coming from. My claim is from playing and listening. – piiperi Reinstate Monica Apr 4 '20 at 22:39
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    This reply is intelligent and makes sense, but you didn't notice that OP refers to a specific theory(LCC), where words like "tonic" have specific meaning. – fdreger Apr 5 '20 at 0:38
  • indeed, in the Lydian Chromatic Concept, 4ths and 5ths and "root notes" of an interval take on an entirely different meaning. i would recommend checking out the first chapter to see what i mean – johnmarinelli Apr 5 '20 at 6:46
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I have never heard of this notion of the topmost note of a fourth being the tonic of the interval, much less intervals having tonicity whatsoever (that only applies to scales). However, I can try to break down why you may think this way, or why you were taught this.

I think the confusion lies in the understanding of tonic. The reason that you may consider the top note of a fourth interval a "tonic" would be because a fourth is just an inverted fifth, which is a much more common interval to resolve on. For example, if a song resolved on the interval G-C, that is a fourth, but since that is essentially an "upside down" fifth, we hear it as resolving in the key of C, and not G. C is the topmost note of that interval. As C is the tonic of the C scale (the mode is irrelevant), and we just established that we are in C, C could be called the tonic of the interval.

It should be made clear that this is not common practice, to my knowledge. I have never heard this being used and I would strongly advise not thinking in this way. However, for the sake of answering the question, I will continue using your terminology.

Let's think about the C major scale. Regardless of what interval you play, C is always the tonic. That's just how scales work. The tonic is always the first note (and namesake) of the scale. Using the logic we used previously, if we were to resolve on a C-F interval, the implied key would be F (any mode but Locrian). So in that sense, sure, F could be the "tonic". However, this completely disregards all the context that the actual key is C, making this a completely flawed way of understanding intervals.

The key you are in C, so it does not matter what interval you play; the tonic will always be C. This doesn't matter for Lydian, Aeolian, Mixolydian, whatever. If the first note of the scale is C, the tonic is C. Any tonicity you may apply to intervals based on the logic we used earlier holds no significance, as that simply isn't how intervals work. Wherever you had learned this is either teaching incorrect information, or has some roundabout approach to theory that I am not grasping the essence of from your question.

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    This is an intelligent answer, but you didn't notice that OP refers to a specific theory(LCC) – fdreger Apr 5 '20 at 0:38
  • Just because C is one of the notes in an interval - lower or higher, doesn't put it into key C. – Tim Apr 5 '20 at 6:52
  • @Tim Where did I say that? It may have come across that way in my wording but I didn't mean for what I said to come across as that – hvksh Apr 6 '20 at 1:05

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