[JonPR]

Originally Posted by ameetnsharma

I guess this is a matter of definition... To me, phrasing emphasizes the mode... meaning I hear the mode clearly when notes are phrased in a particular way... I'd call this a modal difference.

Yes, but it depends on context.

Originally Posted by ameetnsharma

Phrasing plays a role in what my ear decides as the tonic centre... and as a result my ear hears a different tonic, and a different mode. Seems like a definite modal difference to me.

Sure, but if you have a chord sequence in a key, then there is only one tonic, regardless of what chord you're on. You shouldn't be hearing other notes as tonics, although of course you will hear their individual root qualities.
And, if one chord does last a while, then yes you will certainly hear that chord's modal quality - the longer it lasts, the more it will tend to establish itself as a new tonal centre.
But phrasing makes little difference to that, unless you're going for those "modal identifiers", such as the lydian #4, or the dorian major 6, or whatever.

Originally Posted by ameetnsharma

Suppose there are no background chords... just one person on the guitar playing single line notes... he selects from ABCDEFG...

If I play the regular C major scale... I hear an ionian sound.... no background chords or anything... C becomes the tonic centre to my ear because it starts and ends with C.

If I play the F lydian scale... I hear a lydian sound... F becomes the tonic centre to my ear.

Sure. Because now you have no background context, and are establishing the tonal centre yourself.

But there's still a useful distinction here. Playing the C major scale at random - ie the notes ABCDEFG in any order - you should find that C has the most "gravitational pull", the one with most apparent claim to tonal centre; because of the cultural familiarity we all have with "do re mi fa so la ti do". That's the most familiar use of those 7 notes.
In order to make a different note sound like the centre, then yes you do need to emphasise it more.
With no background chord(s), therefore, then yes you need to stress the F more to get an F lydian sound from those 7 notes.

Originally Posted by ameetnsharma

Similarly if I select from these notes with phrasing that centers around F, getting that B in there, my ear will pick up on an F tonic, and a lydian sound. There does not need to be any background chords. Phrasing alone can get you the tonic.

I agree. But that's a somewhat unnatural scenario.

In most discussions about modes and their usefulness, the assumed context is chord sequences, in given songs or tunes. People want to be able to improvise on any song they might encounter, and it's often suggested or implied (wrongly or mistakenly IMO) that modes are a solution, a strategy.
That's a common misapprehension, at least.

Originally Posted by ameetnsharma

If you do add a background chord... F major chord playing repeatedly... and I play a C major single line scale. The lydian is not nearly as apparent to my ear, as compared to playing the F lydian scale... The mode becomes more apparent to my ear when I start on an F...

Again, I agree. Given the single F chord and the C major scale, it sounds lydian anyway without an emphasis on the F, but more so if you stress the F.

But again, that's a rare scenario in the real world.

IOW, it's important to distinguish the idea of one chord jamming - experimentation with modes during practice in order to understand how they work - and the real world application of modes in actual music.
Of course, one can write one's own modal music [see above ], to define one's terms, but in tackling other compositions what matters is to understand (and exploit) the given material, in whatever form it's presented.