In an article I am studying by Daniel J. Pedersen and Christopher Lilley, "Divine Simplicity, God's Freedom, and the Supposed Problem of Modal Collapse," (Journal of Reformed Theology 16, 2022, 127-147),  the authors quote Boethius:

. . . if you know that someone is walking, he must necessarily be walking. (Consolation, v. 6)

They then paraphrase and endorse the point as follows:

That is, supposing a man is walking, so long as he is walking, he must necessarily be walking.

This strikes me as interestingly false. Suppose Tom is walking at time t. Surely he might not have been walking at t. So it is not necessarily, but contingently, the case that Tom is walking at t. For although he is actually walking at t, it is possible that he not be walking at t. Of course, a man cannot walk and not walk at the very same time. For that would violate the law of non-contradiction (LNC). But that is not the issue. The issue is whether the following could be true: Tom is walking at t & it is possible that Tom is not walking at t. And of course it could be true.

Boethius, lately quoted, mentioned knowledge. Is my knowing that Tom is walking at t relevant to the question? Right after the sentence quoted, Boethius writes, "For what a man really knows cannot be otherwise than it is known to be."  Suppose I know (with objective certainty) that Tom is walking at t.  Would it follow that Tom is necessarily walking at t? No. Boethius appears to have committed a modal fallacy.  While it it true that 

1) Necessarily (if S knows that p, then p)

it does not follow that

2) If S knows that p, then necessarily p.

To think otherwise is to commit the modal fallacy of confusing the necessity of the consequence (necessitas consequentiae) with the necessity of the consequent (necessitas consequentis).  (1) is true; (2) is false; hence the inferential move is invalid. Most of the propositions we know are contingent. For example, I know that I was born in California, but this is a contingent fact about me.  I might have been born elsewhere. I might not have been born at all. One cannot know what is false, and so it follows that whatever one knows is true; it does not follow, however, that what one knows is necessarily true.  For again, most of what we know is contingently true.  In the patois of 'possible worlds,' most of what we know is true in some but not all possible worlds.

So we can set aside knowledge that a man is walking as a good reason for believing that a man walking is necessarily walking. Back to walking Tom. He cannot walk and not walk at the same time. But if he is walking at a given time, it is possible that he not be walking at that time, which is to say: Tom's walking at t is contingent, not necessary.  Don't confuse possibly (p & ~p) with p & possibly ~p.  Mind the scope of the modal operator.

The authors do not agree. They follow Boethius, Aquinas (Summa Contra Gentiles I,  67), and other scholastics. While they grant that  it is not absolutely or unconditionally necessary that a man walk, on the ground that there is nothing in the concept human being or the essence human being  to require that an instance of this concept/essence walk, it is hypothetically or conditionally necessary that a particular man walk on condition that he is in fact walking. I will argue against this distinction in a moment. But first:

Modal collapse and DDS

Why is this so interesting? One reason is because it is relevant to the problem of modal collapse that bedevils classical theism. (Classical theists, by definition, are committed to the doctrine of divine simplicity (DDS).)  Here is (one aspect of) the problem in brief compass. God exists of absolute metaphysical (broadly logical) necessity. The ground or source of this necessity is the divine simplicity. On DDS there are no distinctions in God, hence no distinction between God and his creating of our (presumably) contingent universe U.  Since God is omnipotent, his creating of U ex nihilo is efficacious: he cannot fail to 'pull off' what he intends. It is presumably also deterministic: divine efficient agent-causation of U is not probabilistic or 'chancy.'  It would seem to follow that God, his free creating of U, and U itself are all three absolutely necessary.  Now everything is either God or created by God, including so-called abstract  objects. It follows that everything is absolutely necessary and thus that nothing is contingent.  The distinction between necessity and contingency collapses.  The senses of the modal terms, no doubt, remain intact and distinct on the intensional plane; the collapse occurs on the extensional plane. Hence the dreaded modal collapse. This is unacceptable if you believe, as most classical theists do, that creation is contingent, both the action of creating and its effect, the ensemble of creatures. (Note the process-product ambiguity of 'creation.') A separate problem in the immediate vicinity, one that I will not discuss here, concerns whether the contingency of creation requires a libertarian model of divine free agency. 

A response via the distinction between absolute and hypothetical necessity

One among several responses to the threatened collapse of the contingent into the necessary is to say that there is no modal collapse, no reduction of everything to absolute necessity,  because, while God is absolutely necessary, his creatures are not absolutely but only hypothetically necessary.  This distinction is supposed to avert the collapse. I do not believe that this distinction, despite its distinguished pedigree, stands up to close scrutiny.  Let me explain.

If a thing exists necessarily, one may reasonably ask about the ground or source of its necessary existence. In the case of God, if there is such a ground, it would have to be God himself in his ontological simplicity. God is necessary in se, in himself, and not ab alio, from another. This is because God does not and indeed cannot derive his existence from another. In the case of so-called abstract objects such as the number 9 or the set {7, 9} the ground of necessary existence is in God. For abstracta are creatures: they derive their existence from God. Or at least this is a reasonable thing to say. Accordingly, abstracta are necessary ab alio, from another. Given that they too are creatures, they cannot exist in themselves, but are dependent on God for their existence. You might even say that they are hypothetically or conditionally necessary in that they exist only on condition that God create them, and this despite the fact that abstracta exist 'in all possible worlds' in the Leibniz-derived patois of 'possible worlds.' If, per impossibile, God were not to exist, then abstract entities would not exist either, and this regardless of the fact that they 'exist in all possible worlds' just as God does.  There is no harm in speaking of abstracta as hypothetically necessary if all this means is that abstracta are necessary beings that are dependent on God for their existence. There is no harm as long as it is realized that God and the number 9, for example, are necessary in the very same sense with the difference being that God exists unconditionally whereas the number exists conditionally or dependently ('hypothetically').  But then there are not two kinds of necessity, absolute and hypothetical, as the authors seem to think, but one kind only, with however two different sources or grounds of the existence of those items that enjoy this one kind of necessity (absolute metaphysical necessity). By my lights, one must distinguish between the question whether a thing exists dependently or independently from the question whether the thing exists necessarily or contingently.  The two distinctions 'cut perpendicular' to each other. Accordingly, God exists independently and necessarily; abstracta exist dependently and necessarily; poor Socrates exists dependently and contingently.  What holds for Socrates holds for every sublunary creature, every concrete item in space and time that is created by God.  If the universe of sublunary items just exists, brute-factually, as Bertrand Russell maintained in his BBC debate with Fr. Copleston, then Socrates exists contingently but not dependently. If a thing is modally contingent, it does not follow straightaway that it is dependent on ('contingent upon') anything.  On my view, then, modal collapse remains a formidable threat to DDS and thus to classical theism which, by definition, includes DDS.  

What our authors want to say, however,  is not merely that abstracta enjoy hypothetical necessity, but that all creatures, including material creatures in time and space, enjoy this "kind" (the authors' word) of necessity. But this is the Boethian mistake all over again. If Tom is walking at t, it does not follow that he is necessarily walking at t. Likewise, if Tom is being sustained in his existence by divine action at t, it does not follow that Tom necessarily exists at t. No, our man contingently exists at t. For God could decide at t or right before to 'pull the plug' on Tom (or on the entire universe of which he is a part) in which case Tom, who had been in existence moments before, would become nothing. Despite God's ongoing creative sustenance of Tom moment by moment, at each moment he remains possibly nonexistent, which is to say, contingent. (To understand what I just wrote, you have to understand that 'possibly' is to be taken ontologically, not epistemically.)

If I am told that Tom and the rest of the denizens of the sublunary are not modally contingent,  but hypothetically necessary, I will repeat my point that there is no such  modality as hypothetical necessity. The notion is an illicit amalgam that elides the distinction between existence and modality. Everything that exists is either necessary or contingent. And everything that exists either exists dependently or independently. Hypothetical necessity is a misbegotten notion.

Linguistically, the qualifier 'hypothetical' in 'hypothetical necessity' is an alienans adjective, one the shifts ('alienates,' 'others') the sense of 'necessity. In this respect it is like 'apparent' in 'apparent heart attack.' A deciduous tree cannot fail to be a tree; an apparent heat attack, however, may fail to be a heart attack.  'Hypothetical necessity' is  unlike 'deciduous tree' and very much like 'apparent heart attack.' Some heart attacks are merely apparent while others  are apparent and real. (And still others, of course, are real but not apparent.) Similarly, some necessary beings are hypothetical in that they depend for their existence on God; other necessary beings are absolute in that they do not depend on anything.

One mistake is to think that the number 9, e.g., is only hypothetically necessary because dependent on God for its existence. No, it is just as modally necessary as God.  Another mistake is to think that if some creatures are non-contingent, then all creatures are, including the denizens of the sublunary, in plain English, those that are material, temporal, and spatial. Socrates — our representative sublunary critter — is a modally contingent being despite his creaturely  status.   A third mistake is to think that, because divine productive causation ex nihilo necessitates its effect, that the effect is thereby rendered modally necessary. This mistake is structurally analogous to the logical mistake of confusing the necessity of the consequence with the necessity of the consequent.  Whatever God brings into existence out of nothing cannot fail to exist, but that is not to say that the effect of the bringing-into-existence is modally necessary. No, it remains modally contingent, just as modally contingent as the divine action. If you say that the divine action is absolutely necessary, then of course the effect is modally necessary. But then you have nolens volens accepted modal collapse!

In sum, there is no evading the modal collapse objection to DDS by distinguishing between absolute and hypothetical necessity, and this for the reason that there is no such modality as hypothetical necessity. The phrase 'hypothetical necessity' can only mean that certain entities that are modally necessary, the inmates of what Plantinga has called the "Platonic menagerie," are nevertheless  dependent on God for their existence.