Can someone explain Ibn Sina’s propositions that are necessary ‘as long as’?

Question

I model oil reservoirs, and I started reading the history of logic because the Ash'ari material I love keeps assuming you know Ibn Sina. A survey chapter on Arabic logic lost me at one point, and I'd like a patient explanation.
It says Ibn Sina split a sentence like "every A is necessarily B" into several readings. Roughly: necessary for as long as the A exists; necessary for as long as it is described as A; necessary at some definite time; necessary at some time or other. The chapter called the first two by Arabic names I can't reproduce properly, something like dhātī and waṣfī.
My questions:
What is the difference between "as long as it exists" and "as long as it is described as A"? They sound the same to me.Why does it matter? In my world, "every producing well declines in pressure" is true, but only while it's producing. Is that the kind of case he meant?Did this have any influence outside the Arabic tradition, or did it stay there?

Layla Haddad · Accepted Answer

Your well is a perfect example, so let me use it.
Take "every producing well is declining in pressure". On the first reading (dhātī, roughly "substantial"), the predicate belongs to the subject as long as the subject exists: so long as this well exists at all, it is declining. That's false. Shut it in and it is still a well, but it isn't producing.
On the second reading (waṣfī, roughly "descriptional"), the predicate belongs as long as the subject satisfies the description you used to pick it out: so long as it is producing, it is declining. That's true. The difference is whether the condition is the thing's existence or the description "producing".
The point is that Aristotle's modal syllogistic left these conditions implicit, and a lot of its puzzles come from sliding between readings. Ibn Sina put the time condition inside the proposition and then worked out which syllogisms are valid for which readings.
On influence: inside the Arabic tradition it was enormous. Later logicians built standard textbooks on this framework. In Latin Europe the picture is different: his metaphysics and psychology were translated and widely read, but this part of his logic had much less direct impact. Tony Street's survey articles are the most reliable place to go next.

Abdulrahman Al-Qahtani · Answer

Layla, that is the clearest thing I've read on this. So the waṣfī reading is basically a conditional with a time index built in: for all t, if x is producing at t, x is declining at t. Is that the same as what Prior did with tense operators?

Tomasz Wójcik · Answer

Related, but not the same. Prior puts operators in front of whole sentences: "it will be the case that…", "it has always been the case that…". Ibn Sina builds the temporal condition into the truth conditions of the categorical proposition itself, so the time quantifier sits inside, attached to the subject term. Your paraphrase with "for all t" is close to how modern reconstructions handle it. Same spirit, then: neither of them treats time as an afterthought you can ignore when doing logic.

Mona Fathy · Answer

A cataloguer's note. One of those later textbooks, al-Kātibī's Shamsiyya, turns up in our manuscript holdings with layer upon layer of commentary and glosses in the margins. If you ever want to see how seriously students took the distinction Layla describes, look at how much ink was spent on it in the margins.

Hamza Qureshi · Answer

Lawyer's angle: statutes do this constantly and courts have to work out which reading is meant. "A guardian must consent to the marriage of a minor" is about the guardian as long as the ward is a minor, not as long as the guardian exists. Half the disputes I see turn on someone reading a descriptional condition as a permanent one.

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