I think the categories you are using there (physical/metaphysical, falsifiable/unfalsifiable) may turn out to be anachronistic in the context of medieval discussions of what happens to the consecrated elements during the Mass. See for instance the discussion of Thomas Aquinas (c. 1225–1274) in his
TL/DR The substance of the bread becomes the substance of Christ's body; but its accidents (colour, texture - all that we perceive directly) remain those of bread.
Article 4. Whether bread can be converted into the body of Christ?
Objection 1. It seems that bread cannot be converted into the body of Christ. For conversion is a kind of change. But in every change there must be some subject, which from being previously in potentiality is now in act. because as is said in Phys. iii: "motion is the act of a thing existing in potentiality." But no subject can be assigned for the substance of the bread and of the body of Christ, because it is of the very nature of substance for it "not to be in a subject," as it is said in Praedic. iii. Therefore it is not possible for the whole substance of the bread to be converted into the body of Christ.
Objection 2. Further, the form of the thing into which another is converted, begins anew to inhere in the matter of the thing converted into it: as when air is changed into fire not already existing, the form of fire begins anew to be in the matter of the air; and in like manner when food is converted into non-pre-existing man, the form of the man begins to be anew in the matter of the food. Therefore, if bread be changed into the body of Christ, the form of Christ's body must necessarily begin to be in the matter of the bread, which is false. Consequently, the bread is not changed into the substance of Christ's body.
Objection 3. Further, when two things are diverse, one never becomes the other, as whiteness never becomes blackness, as is stated in Phys. i. But since two contrary forms are of themselves diverse, as being the principles of formal difference, so two signate matters are of themselves diverse, as being the principles of material distinction. Consequently, it is not possible for this matter of bread to become this matter whereby Christ's body is individuated, and so it is not possible for this substance of bread to be changed into the substance of Christ's body.
On the contrary, Eusebius Emesenus says: "To thee it ought neither to be a novelty nor an impossibility that earthly and mortal things be changed into the substance of Christ."
I answer that, As stated above (Article 2), since Christ's true body is in this sacrament, and since it does not begin to be there by local motion, nor is it contained therein as in a place, as is evident from what was stated above (Article 1, Reply to Objection 2), it must be said then that it begins to be there by conversion of the substance of bread into itself.
Yet this change is not like natural changes, but is entirely supernatural, and effected by God's power alone. Hence Ambrose says [(De Sacram. iv): "See how Christ's word changes nature's laws, as He wills: a man is not wont to be born save of man and woman: see therefore that against the established law and order a man is born of a Virgin": and] [The passage in the brackets is not in the Leonine edition] (De Myster. iv): "It is clear that a Virgin begot beyond the order of nature: and what we make is the body from the Virgin. Why, then, do you look for nature's order in Christ's body, since the Lord Jesus was Himself brought forth of a Virgin beyond nature?" Chrysostom likewise (Hom. xlvii), commenting on John 6:64: "The words which I have spoken to you," namely, of this sacrament, "are spirit and life," says: i.e. "spiritual, having nothing carnal, nor natural consequence; but they are rent from all such necessity which exists upon earth, and from the laws here established."
For it is evident that every agent acts according as it is in act. But every created agent is limited in its act, as being of a determinate genus and species: and consequently the action of every created agent bears upon some determinate act. Now the determination of every thing in actual existence comes from its form. Consequently, no natural or created agent can act except by changing the form in something; and on this account every change made according to nature's laws is a formal change. But God is infinite act, as stated in I:7:1; III:26:2; hence His action extends to the whole nature of being. Therefore He can work not only formal conversion, so that diverse forms succeed each other in the same subject; but also the change of all being, so that, to wit, the whole substance of one thing be changed into the whole substance of another. And this is done by Divine power in this sacrament; for the whole substance of the bread is changed into the whole substance of Christ's body, and the whole substance of the wine into the whole substance of Christ's blood. Hence this is not a formal, but a substantial conversion; nor is it a kind of natural movement: but, with a name of its own, it can be called "transubstantiation."
Reply to Objection 1. This objection holds good in respect of formal change, because it belongs to a form to be in matter or in a subject; but it does not hold good in respect of the change of the entire substance. Hence, since this substantial change implies a certain order of substances, one of which is changed into the other, it is in both substances as in a subject, just as order and number.
Reply to Objection 2. This argument also is true of formal conversion or change, because, as stated above (Reply to Objection 1), a form must be in some matter or subject. But this is not so in a change of the entire substance; for in this case no subject is possible.
Reply to Objection 3. Form cannot be changed into form, nor matter into matter by the power of any finite agent. Such a change, however, can be made by the power of an infinite agent, which has control over all being, because the nature of being is common to both forms and to both matters; and whatever there is of being in the one, the author of being can change into whatever there is of being in the other, withdrawing that whereby it was distinguished from the other.
Article 5. Whether the accidents of the bread and wine remain in this sacrament after the change?
Objection 1. It seems that the accidents of the bread and wine do not remain in this sacrament. For when that which comes first is removed, that which follows is also taken away. But substance is naturally before accident, as is proved in Metaph. vii. Since, then, after consecration, the substance of the bread does not remain in this sacrament, it seems that its accidents cannot remain.
Objection 2. Further, there ought not to be any deception in a sacrament of truth. But we judge of substance by accidents. It seems, then, that human judgment is deceived, if, while the accidents remain, the substance of the bread does not. Consequently this is unbecoming to this sacrament.
Objection 3. Further, although our faith is not subject to reason, still it is not contrary to reason, but above it, as was said in the beginning of this work (I:1:6, ad 2; Article 8). But our reason has its origin in the senses. Therefore our faith ought not to be contrary to the senses, as it is when sense judges that to be bread which faith believes to be the substance of Christ's body. Therefore it is not befitting this sacrament for the accidents of bread to remain subject to the senses, and for the substance of bread not to remain.
Objection 4. Further, what remains after the change has taken place seems to be the subject of change. If therefore the accidents of the bread remain after the change has been effected, it seems that the accidents are the subject of the change. But this is impossible; for "an accident cannot have an accident" (Metaph. iii). Therefore the accidents of the bread and wine ought not to remain in this sacrament.
On the contrary, Augustine says in his book on the Sentences of Prosper (Lanfranc, De Corp. et Sang. Dom. xiii): "Under the species which we behold, of bread and wine, we honor invisible things, i.e. flesh and blood."
I answer that, It is evident to sense that all the accidents of the bread and wine remain after the consecration. And this is reasonably done by Divine providence. First of all, because it is not customary, but horrible, for men to eat human flesh, and to drink blood. And therefore Christ's flesh and blood are set before us to be partaken of under the species of those things which are the more commonly used by men, namely, bread and wine. Secondly, lest this sacrament might be derided by unbelievers, if we were to eat our Lord under His own species. Thirdly, that while we receive our Lord's body and blood invisibly, this may redound to the merit of faith.
Reply to Objection 1. As is said in the book De Causis, an effect depends more on the first cause than on the second. And therefore by God's power, which is the first cause of all things, it is possible for that which follows to remain, while that which is first is taken away.
Reply to Objection 2. There is no deception in this sacrament; for the accidents which are discerned by the senses are truly present. But the intellect, whose proper object is substance as is said in De Anima iii, is preserved by faith from deception. And this serves as answer to the third argument; because faith is not contrary to the senses, but concerns things to which sense does not reach.
Reply to Objection 4. This change has not properly a subject, as was stated above (Article 4, Reply to Objection 1); nevertheless the accidents which remain have some resemblance of a subject.
Article 6. Whether the substantial form of the bread remains in this sacrament after the consecration?
Objection 1. It seems that the substantial form of the bread remains in this sacrament after the consecration. For it has been said (Article 5) that the accidents remain after the consecration. But since bread is an artificial thing, its form is an accident. Therefore it remains after the consecration.
Objection 2. Further, the form of Christ's body is His soul: for it is said in De Anima ii, that the soul "is the act of a physical body which has life in potentiality". But it cannot be said that the substantial form of the bread is changed into the soul. Therefore it appears that it remains after the consecration.
Objection 3. Further, the proper operation of a things follows its substantial form. But what remains in this sacrament, nourishes, and performs every operation which bread would do were it present. Therefore the substantial form of the bread remains in this sacrament after the consecration.
On the contrary, The substantial form of bread is of the substance of bread. But the substance of the bread is changed into the body of Christ, as stated above (Article 2,Article 3,Article 4). Therefore the substantial form of the bread does not remain.
I answer that, Some have contended that after the consecration not only do the accidents of the bread remain, but also its substantial form. But this cannot be. First of all, because if the substantial form of the bread were to remain, nothing of the bread would be changed into the body of Christ, excepting the matter; and so it would follow that it would be changed, not into the whole body of Christ, but into its matter, which is repugnant to the form of the sacrament, wherein it is said: "This is My body."
Secondly, because if the substantial form of the bread were to remain, it would remain either in matter, or separated from matter. The first cannot be, for if it were to remain in the matter of the bread, then the whole substance of the bread would remain, which is against what was said above (Article 2). Nor could it remain in any other matter, because the proper form exists only in its proper matter. But if it were to remain separate from matter, it would then be an actually intelligible form, and also an intelligence; for all forms separated from matter are such.
Thirdly, it would be unbefitting this sacrament: because the accidents of the bread remain in this sacrament, in order that the body of Christ may be seen under them, and not under its proper species, as stated above (Article 5).
And therefore it must be said that the substantial form of the bread does not remain.
Reply to Objection 1. There is nothing to prevent art from making a thing whose form is not an accident, but a substantial form; as frogs and serpents can be produced by art: for art produces such forms not by its own power, but by the power of natural energies. And in this way it produces the substantial forms of bread, by the power of fire baking the matter made up of flour and water.
Reply to Objection 2. The soul is the form of the body, giving it the whole order of perfect being, i.e. being, corporeal being, and animated being, and so on. Therefore the form of the bread is changed into the form of Christ's body, according as the latter gives corporeal being, but not according as it bestows animated being.
Reply to Objection 3. Some of the operations of bread follow it by reason of the accidents, such as to affect the senses, and such operations are found in the species of the bread after the consecration on account of the accidents which remain. But some other operations follow the bread either by reason of the matter, such as that it is changed into something else, or else by reason of the substantial form, such as an operation consequent upon its species, for instance, that it "strengthens man's heart" (Psalm 103:15); and such operations are found in this sacrament, not on account of the form or matter remaining, but because they are bestowed miraculously upon the accidents themselves, as will be said later (III:77:3, ad 2,3; Articles 5 and 6).
I don't think we can reasonably call Aquinas's discussion 'pious superstition', can we?
