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In Group 1, the tones in each pair are separated by a semitone. The semitone can be graphically depicted as follows:
Here the red ovals represent a semitone, C-C#. Moving from C to C# constitutes a tonal ascent, while moving the other way around would constitute a descent. It would be difficult indeed to imagine movement from C to C# as a descent. To visualize this, we would have to imagine that in order to get from C to C#, we should move the long way around the circle, moving counter-clockwise. Just as the eye is far more predisposed to see this ascent in terms of a clockwise movement -- by virtue of proximity -- so too does the ear want to hear any such sequence as a tonal ascent.