Some people have asked me if this theme has to be performed legato or in a articulated style. I have heard both versions being performed.
The legato style of performance have come to the organ from the Romantic piano tradition and it stayed for a long time. Even today there are organists who are not aware that articulated performance style even exists. Whether they practice or perform on the organ, they apply legato touch.
Since Bach's Passacaglia is a Baroque composition, we must apply the articulate legato touch which was called the "Ordinary Touch" in this period.
So we have to articulate the theme quite prominently when we play it on the organ, even with a feeling of alternation between strong and week beats. That's possible to achieve if you shorten the third beat.
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