MrPedantic: Hello Dr J
I believe that "must" derives from the past tense of OE "motan". So it's rather the case that "must" has lost its present tense!
Excuse me for butting in, but I'm puzzled as to what you mean, Mr P.
Interestingly, "would" in the sense with which it appears in this passage (akin to "used to") has only a past meaning.
I'm also puzzled here, Sir. The meaning of 'would' here, to my mind, is not the 'would' that is akin to 'used to'.
After reading DCPaco's reply again, I see he also stated that this was the 'would' of a commonly occurring past action, which, again, I believe is not true. This describes repeated actions but not the common repeated action of the used to/would variety, eg.
"My mother would stroke my forehead to help me get to sleep".
Also, IMO, this 'would' doesn't have a past meaning. It has a meaning that points to a repeated but not habitual action.
"A full moon rose, and still the battle wore on. An hour passed, then another; the combatants staggered and limped. Each time one knight would muster the strength to launch an attack, the other would somehow find the strength to repulse it.
Twice the two knights fell and lay on the ground gasping, watching each other. But each time one would finally struggle to his feet, the other would stand as well."