In Der Gevatter Tod, Death instructs his godson, the doctor, to say certain things when making a call, as follows.
Wenn du [der Arzt] zu einem Kranken gerufen wirst, so will ich [der Gevatter Tod] dir jedesmal erscheinen: steh ich zu Häupten des Kranken, so kannst du keck sprechen, du wolltest ihn wieder gesund machen, und gibst du ihm dann von jenem Kraut ein, so wird er genesen; steh ich aber zu Füssen des Kranken, so ist er mein, und du musst sagen, alle Hilfe sei umsonst und kein Arzt in der Welt könne ihn retten.
Suppose what Death wanted the doctor to say was, "I'll be twenty-one tomorrow," or "I am going to throw up," or "I'm going to have an epileptic fit." (Obviously not in the same circumstances as set out in the original story.)
Can that be rendered as follows:
... so kannst du sprechen, du wolltest morgen 21 Jahre alt sein...
... so kannst du sprechen, du wolltest erbrechen...
... so kannst du sprechen, du wolltest einen epileptischen Anfall haben...
The question of grammar involved in these examples is whether wolltest signifies, in some context, simply what was going to happen without a reference to anyone's volition.
Becoming twenty-one, vomiting, and having an epileptic fit are intended as examples of events beyond anyone's control (and therefore volition). The doctor then, speaking as imagined above, would not be saying that he wanted or intended to do any of those things, but only that they were going to happen.
If so and if wolltest can be used in such context, we seem to have proven (demonstrated) that at least in some context and in some German (Grimms') the modal verb wollen can be exactly like werden insofar as it is 100% future and 0% volition.
This question arose from another, which was more general in scope than this. Thanks.