The LEM dictates that P must be either true or false. — Metaphysician Undercover

Not for all P. P must have certain qualities to be either true or false: call it truth-capable or false-capable. Lacking those, the LEM, then, simply does not apply.

On Interpretation, Part Nine:
"Let me illustrate. A sea-fight must either take place to-morrow or not, but it is not necessary that it should take place to-morrow, neither is it necessary that it should not take place, yet it is necessary that it either should or should not take place to-morrow. Since propositions correspond with facts, it is evident that when in future events there is a real alternative, and a potentiality in contrary directions, the corresponding affirmation and denial have the same character.

This is the case with regard to that which is not always existent or not always nonexistent. One of the two propositions in such instances must be true and the other false, but we cannot say determinately that this or that is false, but must leave the alternative undecided. One may indeed be more likely to be true than the other, but it cannot be either actually true or actually false. It is therefore plain that it is not necessary that of an affirmation and a denial one should be true and the other false. For in the case of that which exists potentially, but not actually, the rule which applies to that which exists actually does not hold good. The case is rather as we have indicated." Italics added.

These are two very distinct ways of looking at inertia with completely different implications. But which one is correct? — Metaphysician Undercover

And here we are at absolute presuppositions. They're both absolutely presupposed in their respective systems. Not,, then, a question of right, but of efficacy. You mention the "force" of gravity. Absolutely, and it works: F = G(m1)(m2) / r^2. F of course for force. The only trouble being that these days and for some time, gravity has been understood not as a force, but as a curvature of spacetime, objects merely following shortest distance paths, geodesics, through spacetime. Gravity as force is a sometimes convenient fiction, and the math works well-enough, but not how it works according to best understanding.

So we're back to models. And your point remains obscure and obscured.

Not for all P. P must have certain qualities to be either true or false: call it truth-capable or false-capable. Lacking those, the LEM, then, simply does not apply. — tim wood

Yes that's what I was saying, we have an exception to the rule, the rule does not apply. Sorry if I didn't express myself clearly.

One of the two propositions in such instances must be true and the other false, but we cannot say determinately that this or that is false, but must leave the alternative undecided. — tim wood

As argued by scholars who have followed Aristotle, it is somewhat unclear what is meant by 'one must be true and the other false' in this context.

In this case it would have been clearer if he had said 'either one or the other must be true". It is important to understand the difference between these two ways of expressing this, because in the latter, truth or falsity is assigned to the relation between the propositions, which is expressed as "one or the other". So truth is a property of that proposition, "one or the other", and not the property of any one of the two propositions. We can say "one will happen", because this does not specify which one will happen, while implying that the other is excluded by the happening of the one. But we cannot unambiguously say "one must be true", because at that time neither is true. If you read the entire section this ought become clearer to you. And the ambiguity is evident in the years of debate which followed.

The best description in On Interpretation is found at 19a 7-23:

Yet this view leads to an impossible conclusion; for we see that both deliberation, and action are causative with regard to the future, and that, to speak more generally, in those things which are not continuously actual there is a potentiality in either direction. Such things may either be or not be; events also therefore may either take place or not take place. There are many obvious instances of this.
...
It is therefore plain that it is not of necessity that everything is or takes place; but in some instances there are real alternatives, in which case the affirmation is no more true and no more false than the denial; while some exhibit a predisposition and general tendency in one direction or the other, and yet can issue in the opposite direction by exception.

Of course Aristotle's best treatise on potentiality (that which may either be or not be) is found in his Metaphysics, a a large section of that text is devoted to this, and a thorough reading is required to understand what he is saying. Here he expounds on the principle established in his Physics, that the concept of "matter" serves to represent the real existence of potentiality in the field of physics.

And here we are at absolute presuppositions. They're both absolutely presupposed in their respective systems. Not,, then, a question of right, but of efficacy. You mention the "force" of gravity. Absolutely, and it works: F = G(m1)(m2) / r^2. F of course for force. The only trouble being that these days and for some time, gravity has been understood not as a force, but as a curvature of spacetime, objects merely following shortest distance paths, geodesics, through spacetime. Gravity as force is a sometimes convenient fiction, and the math works well-enough, but not how it works according to best understanding.

So we're back to models. And your point remains obscure and obscured. — tim wood

That's exactly the point, the nature of the presuppositions affects the efficacy of the model. These models are all effective in some situations and less so in others. That the model becomes ineffective when pushing its boundaries, or parameters, is evidence that it is deficient. Notice that the ineffectiveness is within the boundaries, when the model approaches its boundaries, not outside its boundaries (in which case it wouldn't even be applied), therefore the deficiency is within the model itself, attributable to faulty presuppositions.

My point remains, and is not at all obscure. The presuppositions employed by the models of modern physics fail to account for the difference between past and future, the future holding real possibility. These models are inertia based models based in the assumption (presupposition) that what has been in the past, will necessarily continue to be in the future, unless 'forced' to change.

This presupposition is directly contrary to what Aristotle demonstrated as the nature of "matter", holding the capacity to either be or not be, allowing for the reality of free will. What is clearly described by Aristotle is that there is no such necessity with regard to future events, as distinct from past events. So the necessity attributed to inertia is a false necessity, not a true property of "matter" as defined. It is posited for the sake of producing effective models, making it a pragmatic presupposition which is necessarily untrue because it contradicts the definition. Matter has no properties, properties are formal. So the models break down and fail near their limits, due to the reality that the necessity assumed (as inertia) is a false (contradictory) necessity.