Jtdcftul

So far in my music learning journey I've been quite happy with the Whole, Whole, Half, Whole, Whole, Whole, Half tone construction of major scales. That is until I came across the D Major Scale. D E F# G A B C#
Why does D Major Scale end in C#, surely that is a whole tone up from B not a half, why is the last note not C?

"Whole, Whole, Half, Whole, Whole, Whole, Half " takes you from D to the D an octave higher. The last half is the gap between C# and D.

T T S T T T S is the pattern for major scale notes. So W W H W W W H, as you state, is another way to describe it. Look at the last part - it's a semitone, or a half step, isn't it? That then is the space between the penultimate note and the root note again. A half step below D has to be C♯.

Maybe the confusion is that TTS etc is the 7 intervals between the 8 notes. Scales start and end on the root.

You're right that B to C# is a tone, but that gap is the one before the S. TTSTTS. Making the major in D D E F♯ G A B C♯ D

I've been quite happy with the Whole, Whole, Half, Whole, Whole, Whole, Half tone construction of major scale:
How was this with understanding the major scale of G?

C-D-EF-G-A-HC

G-A-HC-D-EF-G??? -> EF is a halfstep between the 6th and 7th degree!
What we need is a whole step from 6 to 7 and a half from 7 to 8:

We get there by raising the 7th degree by a #:

F needs a sharp # to become a major 7 and we have a new scale with a lead tone F#.

look at this picture:

If you start with D then the 6th degree is B. We want to have now a step of a whole tone between 6 and seven but B-C is only a halftone: the 7th degree must be C#, (as before F as the 7th degree of G had to be raised to F#.

If you split the C major scale between F and G you get 2 identical half parts (TETRACHORDS) WWH and WWH with a W (whole tone) between these tetrachords.

You can develop all major scales of the circle of fifths by cutting the upper half of a scale (2nd tetrachord) and notate it as the 1st tetrachord as it has they have the same distance (intervals).

You will get now a new scale that begins with the 5th degree of the scale we had before. Then you continue adding (constructing) the 2nd tetrachord of this new scale.

You can continue with all half parts of the scales in the same way and you will discover that you'll always have to raise the seventh degree by adding a sharp # to get a halftone at the last step 7-8 and construct by this a scale with a lead tone to the tonic (root tone of the scale or 1st degree = I).

If you follow this indication you will develope all #-scales and also the circle of 5ths and you will understand what you are doing and where the circle comes from.

The scale with flats below on the other site of the circle of 5ths will be explained another time or you may find it out yourself now.