In one reading lesson in my textbook, "dum" is used twice. It had been a long time since I had encountered the word, but the lesson itself reminded me of its usage.
The problem was the usage of the verb outside the clause, the one which defines the action taken at the same time as the "dum" clause. The first sentence speaks of a king:
"Tandem dum castra ut consuetudo erat perlustrat, lucem in tabernaculo vidit."
I thought, 'All right; while he "is walking" through the camp he "saw" a light.' It makes enough sense that dum should be used with the present, from a linguistic standpoint. But then the second sentence showed up. It describes the actions of a soldier:
"Dum multa verba de periculis belli [etc.] scribit, subito regem videt."
It's the same verb, the same basic principle, so why the different tense? Does subito perhaps necessitate the present tense? Maybe because it's a sudden action of noticing, whereas the action of seeing the light during an amble is almost frequentative or progressive? Why, here, does it say "While he is writing, suddenly he sees the king," and then the next verb is "dixit," right back to the perfect?
Ultimately my question is: What is the difference between these two usages, and why are they different?
Is it possible that it's nothing more than a narrative custom, a habit of Latin to say things in the present tense when they took place in the past? I have to admit I haven't seen much evidence for that, but storytelling in English often incorporates the present.
Sorry if I confuse the issue with my own speculations. Much obliged for any and all insight on the matter.