I first heard about tritone substitutions on Paul,s podcast and i took many hour long walks listening to the download on my mp3 player.The out come was i just couldn,t seem to get my head round the subject and i just moved on to another podcast subject eventually.Because although i understood what it was all about what was the stumbling block was i was forever trying to relate the tritone to the the I chord of the scale.Then just yesterday i was browsing at another website teaching music theory and during the course of my reading it again dealt with tritone substitution But with two diagrams.One was of the circle of 5ths and another was of the the circle of 5th but with the clockwise 12 steps starting with C and progress a half step ie C TO C# TO D etc and back all the way round to C.
So if for instance my I in my scale is C i would obviously be looking for a tritone substitute of C# to resolve to C .
Pretty obvious i knew that but so what.Well if i look back to the circle of 5ths and tritones being ambigous in that they share the 3rd and 7th with another chord.Dead opposite and across the circle of 5ths to C
was F#.Yes the common chord to C7 F#7 Both sharing the same tritone.
Well apart from that so what you might ask because your looking for the tritone substitute of C# if your resolving to C.
Well maybe like others i had beeen confused by relating this tritone substitution practise with two triads of a 3 note chord construction and not to two 7th 4 note chord constructions.Then in turn both reduced to a two note shell case construction for jazz tritone substitution.
But here,s the thing too when your wanting to find the tritone substitution for Resolving to C you look on the opposite side to where C#
is on the halfsteps note circle then relate that position to the circle of 5ths.
So we have c# on the half step circle opposite g.
Then there is the same two positions on the circle of 5th taken by yes you guess it G and C#/Db.

Sorry I didn't understand much of your post....( I will one day, that's why I joined this fourm)........ however I like your blue car in your avatar

Cheers
Jimu

Sunfly,

Could you share the link to that web site? If we could see those diagrams it may help to follow what you describe.

Sometimes it's easier not to think about why the tri-tone substitution works, just remember the tri-tone interval. So, to substitute for a C7 think of the note three tones above (or below) C which is F#(Gb) and substitute F#7 for C7. Hence the tri-tone sub for G7 is C#7 and so on.

The way this is worked out is where people often get tripped up. You take the III and the VII of the C7 chord which are E and Bb then figure out what chord uses the VII of C7 as its III i.e., which dominant chord uses Bb as its Maj 3rd - it's Gb7 (F#7).