Daniel Shields

Some theists appeal to science for support of cosmological arguments. Their opponents tend to call attention to various cutting-edge theories of quantum gravity and cosmology. They say that the availability of an abundance of such theories shows that science does not support the thesis that the physical universe depends on a cause outside itself, despite the obvious implications of the well-established theory of general relativity. J. Brian Pitts has the following to say about cosmological arguments that appeal to science:

“It is often suggested that potentially non-singular rivals to GTR [the General Theory of Relativity] are speculative, whereas GTR is well confirmed, so GTR and its retrodiction of the Big Bang singularity ought to be accepted as the default view that challengers need to overcome with better empirical results. . . . The grain of truth in this objection sometimes conceals the grain of falsehood that it also contains. Though not entirely trivial, it is possible to construct theories that reproduce the empirical successes of GTR in all tested regimes to date, but which differ in the ultra-strong field regime relevant to Big Bang cosmology. Granting the success of weak and medium field tests of GTR involving light bending, gravitational redshifting, time delay, and the like, why think that GTR, rather than one of its (perhaps not yet proposed) competitors that fits the data currently in hand, is the right extrapolation?” (“Why the Big Bang Singularity Does Not Help the Kalam Cosmological Argument for Theism,” 2018, p. 96)

The point Pitts is making only has force if one is looking to science for proof of one’s thesis, in this case proof of the universe having a beginning. For the possibility or even actuality of alternative, empirically adequate theories ruins the validity of one’s inference. But it is foolish to look to empirical science for proof of a philosophical thesis in the first place. Scientific theories are always under-determined by the evidence available, and are always subject to revision in light of new theories and new evidence.

Proponents of theistic cosmological arguments who turn to science for support, however, are not looking for proof, but rather for confirming evidence that increases the likelihood of their conclusion. (If they give proofs, they are philosophically based and not scientific.) But speculative scientific theories–such as various versions of quantum gravity–even if empirically adequate, do not have equal weight as evidence compared to well-tested and established theories such as general relativity and quantum mechanics. Why not?

Any theory that is well established, such as GR, was once an untested, speculative theory. It became well-established because it did three things. First, the theory had to have a certain intrinsic plausibility to it and be well-motivated. In GR’s case, it seemed the logical extension of special relativity. But the plausibility of a theory is, to a certain extent, a philosophical question. The fact that the scientific community finds the theory plausible is only a weak argument from authority. For every speculative theory that eventually becomes well-established there are many more speculative theories that end up being discarded and forgotten.

The second thing a new theory should do is it to explain an already known phenomenon that the previously established theory cannot explain. In the case of GR it was the precession of the perihelion of Mercury’s orbit. This made the physics community take GR more seriously, but it wasn’t enough to turn GR into an established theory.

The third thing a new theory must do is to make a new prediction of a previously unobserved phenomenon and gain empirical confirmation of this new prediction. In the case of GR this was the bending of light passing near the sun. Further empirical confirmation of other new predictions increases the likelihood of the theory.

New speculative theories that fit the observed data but have neither explained previously unexplained phenomena, nor made new confirmed predictions, carry much less weight. This is because it is always possible to construct on demand new hypotheses that fit the already observed data. The fit between the theory and the data is not really evidence for the theory if the fit is manufactured ahead of time. It just shows the theorist’s skill with math. In other words, one would expect the theory to fit the currently available data whether the theory is true or false. And given that there are uncountably many such theories that all fit the evidence, the fit does not appreciably raise the theory’s likelihood. (This does not mean the theory is bad as a theory. If it makes a new prediction it is testable and hence scientific. But no one outside the field in question needs to take it seriously until it is confirmed. It cannot claim to be “the science” or to have the evidentiary weight and authority of science.)

The well-established theory, on the other hand, has already had to make a large number of bets in which it risked being shown inadequate, and it has come through repeatedly vindicated by the experimental evidence. This shows that its empirical adequacy is not artificially constructed. It is not at all likely that it would make so many new empirical predictions that were then confirmed if it did not get something right about the nature of reality. Thus well-established theories like general relativity have a significantly higher likelihood of being right than untested speculative theories.

This does not mean that it is overall likely that general relativity is fully correct. It needs somehow to be reconciled with quantum mechanics and we can’t yet predict what the reconciling theory will look like or what implications it will have for the beginning of the universe. Unless there are convincing philosophical arguments for a beginning to the universe, one can reasonably suspend judgment. But it is clear that the overall balance of the scientific evidence does make the universe having a beginning more likely.

On the other hand, an untested new theory, or an alternative theory empirically equivalent to an accepted theory, can make a case for its superiority in virtue of being intrinsically more plausible or providing a better explanation of the phenomena. But that is not a scientific claim and the theory cannot claim the mantle of scientific/empirical authority. It is, rather, a philosophical claim and has to be evaluated philosophically. The proponent of such a theory has to make his principles and reasoning clear and not just rely on the fact that he has a “scientific theory.” He must be prepared that his audience may not share his evaluation.

My recent paper, “Getting Lost with the Menataculus,” (available on the writings page of this website) makes some points about the relevance and irrelevance of appeals to contemporary science in philosophical discussions. I point out that the mere fact that beginningless, naturalistic cosmological models exist is irrelevant to determining whether the scientific evidence supports the thesis that the universe has a beginning or not. Only scientific theories that have made confirmed empirical predictions are admissible evidence in the court of best explanation.

But in my paper I included two very different sorts of arguments under the term “appeals to authority.” Really, appeals to science can be one or the other of two different sorts of argument. Such appeals can be relatively strong abductive arguments, that is, arguments to the best explanation. To the extent that a scientific theory has made empirical predictions that are later confirmed by experiment and observation, it has strong abductive weight. And the more confirmed empirical predictions it has made the stronger its weight. Appeals to science in philosophical discussions can only have strong abductive weight when they are appeals to strongly confirmed theories. And the various appeals to beginningless cosmological models that Linford makes in criticism of theistic cosmological arguments are not of this kind.

The other kind of appeal to science is an argument from authority in the correct sense: scientists who are at the top of their field are smart people and their opinions should be given serious consideration. An argument to scientific authority carries more weight if there is a consensus among scientists on the topic. Most of Linford’s appeals to contemporary cosmological models do not meet this requirement.

But as the great logician Boethius said, argument from authority are the weakest form of argument. Even when there is a consensus among scientists it is often just due to an intellectual fad. Anyone who spends time studying the history of science and of thought in general will be convinced of the weakness of arguments from authority. But I say “weakness,” not “invalidity,” for such arguments are not of no value. Rather, they have a very small value.

One might worry about my own appeal to the GRW theory of quantum mechanics later in the paper. This theory has made empirical predictions but so far they have not been confirmed. That would be a misunderstanding of my argument, but I should have been more clear. I have no attachment to GRW theory or the Diosi-Penrose theory, or any theory in particular. Nor am I even making an abductive scientific argument at that point in the paper. Rather, I am considering the current state of empirically confirmed quantum mechanics, thermodynamics, and statistical mechanics. Conceptual analysis shows that the only plausible philosophical interpretation of the current state of science is that wave function collapse is objective. I am making a philosophical, conceptual argument that some form of objective collapse is necessary. GRW theory and the Diosi-Penrose theory are just two specific proposals out there for objective collapse, and they have value as illustrations. I am not making a scientific argument with them, neither an abductive one nor an argument from authority.

The International Journal for Philosophy of Religion has accepted for publication my paper “Getting Lost with the Mentaculus: Linford, the Second Law of Thermodynamics, and Cosmological Arguments.” I respond to Daniel Linford’s criticisms of the use of big bang cosmology and thermodynamics in theistic cosmological arguments. Linford argues that either the direction of time and causality is reducible and the universe can “begin” without a cause, or the direction of time and causality are non-reducible and the universe need have no beginning. He appeals to the “Mentaculus” account (associated with David Albert and Barry Loewer) of the reduction of thermodynamics to statistical mechanics to support his view of reducible time and causality. I argue that not only does Linford mischaracterize proponents of cosmological arguments, but the classical version of the Mentaculus fails to justify a reducible view of time and entropy increase. The past hypothesis together with time-symmetrical dynamical laws cannot explain the parallel direction of entropy increase experienced by isolated branch systems. Time must have a fundamental arrow and entropy increase is fundamentally asymmetrical in time. The second law of thermodynamics has a “statistically absolute” character connected with irreversible, objective collapse of the quantum wave function. Linford’s naturalistic bounce cosmologies are excluded on the grounds that their extended entropy reducing phases violate the second law. I further critique the role that speculative models of physical cosmology have played in debates over theistic arguments and respond to two common objections against appeals to entropy by proponents of cosmological arguments.

The analysis of inertial motion in my previous post can be extended in a straightforward way to spherical and hyperbolic universes. In spherical and hyperbolic universes also, if a cosmological constant is present and the expansion never ending, then any inertially moving object will come to rest with respect to space on its own without any forces acting on it. (The space still expands, and so the object’s distance from an observer still increases.)

The mathematical analysis is simplified if one utilizes an alternative system of coordinates. In my previous analysis I was using the following standard form of an FLRW metric:

This is, of course, simplest to work with when the universe is flat (k = 0). When k = 1 the universe is spherical and finite in size. The variable r is the radial component from the origin. If it were possible to travel far enough in a single direction one would return to where one started. When r = 1 the position is one quarter of the way around the entire universe. In the opposite direction, r = 1 would be another quarter of the way around the universe. But r = 1 is also a coordinate singularity since one ends up dividing by zero. Another standard version of the FLRW metric avoids this problem and covers the entire spherical universe:

When k = 0 (flat universe), sigma of chi = chi and these coordinates are identical to the previous coordinates. When k = 1 (spherical universe), sigma of chi equals the sine of chi. When k = -1 (hyperbolic universe), sigma of chi equals the hyperbolic sine of chi. In a spherical universe, when chi goes to pi one has gone half way around the universe. Chi going to pi in the opposite direction then covers the other half of the universe.

From this metric one can derive the connection coefficients. We are interested in the case of radial motion only, and so the following connection coefficients (for the k = 1 case) are the only ones relevant:

The geodesic equation then gives:

Presuming that the velocity is much less than the speed of light, gamma is approximately one. If the velocity is appreciable compared to light, gamma will be more than one and the deceleration will be greater.

The geodesic equation has given us a differential equation, which, under the simplifying assumption that gamma is a constant equal to one, is solved by the following equation:

The distance covered by the object’s proper velocity (as opposed to the comoving velocity of space) is given by:

If the universe has a cosmological constant and a density low enough not to recontract and end in a big crunch, then eventually the scale factor increases as

Thus the total distance covered by an inertially moving object in infinite time is (H is the Hubble parameter which approaches a constant value determined by the cosmological constant):

A nearly identical analysis applies to a hyperbolic universe (k = -1.) Thus inertially moving objects not only slow down and approach a state of rest, but approach a terminal point in space. This might be welcome news to Aristotelians.

In my book Nature and Nature’s God I claim that inertia is compatible with Thomistic natural philosophy. The fact that inertial motion continues on its own without an impelling force is not a real problem, as I show that for Aquinas motion in general does not require a continuously conjoined mover. The greater difficulty is the fact that inertia seems endless both in the sense of continuing forever and in the sense of having no goal. For Aquinas, every motion has its terminus.

I argue in the book that inertial motion, even though in principle infinite, has an effective terminus: complete isolation of a body from all interaction with other bodies. Not every Thomist I have communicated with has been comfortable with this solution. But I have since learned something very interesting about force-free motion in general relativity (GR). (Note that gravity does not count as a force in GR.)

In an expanding spacetime an object traveling force-free (no friction or any other retarding forces) in an empty expanding space decreases its proper velocity over time. In the simplest realistic case, every object asymptotically approaches a velocity of zero and also asymptotically approaches a limiting position in space. Its distance, however, from an observer will still increase because the space itself is expanding. The object, however, has no motion of its own (it “comoves” but has no “peculiar velocity.”) The simple but realistic case I have in mind is that of a flat, matter filled universe with a cosmological constant of sufficiently large value to prevent collapse and cause eventual runaway expansion. This is more or less the standard model of cosmology right now; the geometry is at least very close to flat, and dark energy is frequently interpreted as the cosmological constant, although this is currently under debate. The conclusion of a limiting position for a force free object may also hold in more complicated cases (e.g., positive spatial curvature, non-exponential expansion) but I have not been able to work through the more complicated mathematics.

An intuitive way to see why this phenomenon would occur so is to consider cosmological redshift. As the universe expands waves traveling through it are stretched thus undergoing redshift. This redshift applies not only to light but to the DeBroglie waves of massive objects. The DeBroglie wavelength of an object is inversely proportional to its momentum. Thus as the DeBroglie wave of a massive object traveling through space is redshifted and its wavelength increased, the momentum of the object decreases. Thus its proper velocity also decreases.

The more direct GR approach is to start with an FLRW metric. The metric determines a set of connection coefficients ($\Gamma_{\mu\nu}^{\alpha}$). If one plugs these connection coefficients into the geodesic equation ($\frac{d^2x^{\alpha}}{d\tau^2}=-\Gamma_{\mu\nu}^{\alpha}\frac{dx^{\mu}}{d\tau}\frac{dx^{\nu}}{d\tau}$), and makes the simplifying assumption that the motion is entirely in the radial direction ($d\theta=d\phi=0$) one obtains the differential equation $\frac{d^2r}{d\tau^2}=-\left(\frac{kr}{1-kr^2}+2\frac{\dot{a}}{a}v^r\gamma\right)$. If one assumes that the object’s speed is non-relativistic ($v \ll c$) so that the gamma factor can be neglected and that the universe is flat (k = 0) then the equation is easily solved to yield that $v = v_0 a^{-2}$, where a is the scale factor and $v_0$ is the object’s initial speed. If the scale factor increases exponentially with time, as the cosmological constant eventually causes to happen, then the distance covered by the object’s proper velocity is finite, that is $\int_{t_0}^\infin av dt$ is finite. A significant gamma factor value only increases the rate of deceleration, so this result should also hold for relativisitic speeds.

This means that a Thomist uncomfortable with infinite inertial motion may be able to avoid it without denying contemporary physics. Nevertheless, such a conclusion would require a universe whose expansion has no terminus. Thus the individual locomotion of objects in the universe might have a terminus, but not the growth motion of the universe itself. Whether this is helpful or not for a Thomist I leave to further reflection.

UPDATE (June 4th, 2026): I have extended the translation to include question 3 as well, “Does the good will have only one end or can there be many?” St. Bonaventure argues that there can only be one principal end but that there can be multiple subordinate ends. An updated file is available on the Writings page.

I have added to the Writings page of this website a translation of St. Bonaventure, In II Sent. d. 38, a. 1, q. 2, on the question “What is the end that by its goodness makes the will good, and to what ought our wills be referred in order that they be upright?” St. Bonaventure argues that charity, uncreated and created, is the end of the good will. His position here should be compared and contrasted with that of St. Thomas Aquinas (see ST I-II, q. 1-5.) My article “St. Bonaventure, St. Thomas, and Eudaimonism” explores this topic.

James Dominic Rooney, O.P. has reviewed my book Nature and Nature’s God for the American Catholic Philosophical Quarterly. Fr. Rooney begins his review: “Could another book on Thomas Aquinas’s “five ways” for proving the existence of God add something that has not yet been said? Yes, indeed it can.” He states that “Shields’s book presents overall a comprehensive and engrossing account of how to defend Thomistic natural philosophy within the context of contemporary physics.” “The case is presented cleanly; the responses to objections are generally compelling and plausible. Shields does a particularly good job of illustrating and defending a turn to philosophy of science that can enhance the work being done in philosophy of religion. His book will be essential reading for those who want to defend arguments for the existence of God within our contemporary scientific context.”

I thank Fr. Rooney for his kind words.

Of course, Fr. Rooney also has criticisms of some aspects of my book. I would like to respond to those here.

Fr. Rooney seems to read my account as turning the unmoved mover argument into a natural scientific argument (e.g., p. 667 of the review.) He later says that it seems to him to be “fundamentally an abductive argument” (p. 669.) But in the book I said that the unmoved mover argument is a philosophical, not a scientific one; the science only confirms/corroborates the philosophical argument rather than refutes it, as commonly thought. The unmoved mover argument as I present it is not abductive but rather deductive and demonstrative. Yet the argument is not a metaphysical argument; it is a natural philosophical argument. The significance of this distinction is often missed by modern Thomists. Aquinas, however, describes metaphysics, natural philosophy, and natural science (what he called “middle science,” that is, applied math) as three formally distinct disciplines. Some of Fr. Rooney’s criticisms may be based on a misunderstanding here.

Fr. Rooney also states that “Aquinas’s argument has been thought by many prominent interpreters (e.g., Weisheipl) to rely on a problematic premise that everything ‘being moved’ requires a mover whose action is somehow simultaneously bringing about that motion, which Shields concedes would be false in light of inertial motion.” But Fr. Weisheipl is not a prominent interpreter of Aquinas’ First Way. As far as I know he never gave an account of the unmoved mover argument in print. What he does say suggests that he would interpret the argument as focusing on substantial change. Fr. Weisheipl does, however, read the mover principle as “everything being moved requires a mover”; he therefore exempts natural motion from the mover principle. I do see this as problematic and argue against it in the book. (The great merit of Fr. Weisheipl’s work, however, is that he shows that Aquinas does not think that every motion requires a continuously conjoined mover.) What I see as more problematic is that some interpreters, such as Fr. Garrigou-Lagrange, read the mover principle as “everything in motion is being moved by another” and then deny the existence of truly inertial motion, requiring God to carry bodies along so to speak. Others interpret the First Way as hinging on the act of existence (Owens, Knasas, and Kerr for example) and yet there is no reference to the act of existence at all in the text of the First Way. What I argue in the book is that the mover principle should be read “everything in motion is moved by something else” but that the mover may have acted in the past to cause present motion. This makes it possible to reconcile the unmoved mover argument with modern physics.

Fr. Rooney also says that I allege “that Aquinas’s argument only pertains to physical motion and that Aquinas only later establishes the act/potency distinction in a subsequent logical move (esp. 96–100). I fail to see, however, that the ‘first way,’ even as Shields presents it, can be defended without the act/potency distinction.” While it is true that I read the First Way as pertaining only to physical motion, the rest of this is a mischaracterization of my book. I discuss the act/potency distinction in chapter one in the course of explaining the mover principle. Certainly the act/potency distinction is necessary for understanding the First Way. What I say, however, is that the thesis that God is pure act is not part of the First Way. It is only established in q. 3, a. 1, and not by an appeal to the First Way but rather to the Fourth Way.

Fr. Rooney continues the criticism by saying that “these same claims [about the necessity for an immaterial mover for everlasting motion] end up ramifying into precisely the considerations about God lacking any potency at all, since the arguments require ultimately a mover that undergoes no change in entropy and has no potency for any change. So Shields cannot fault these other interpretations for incorporating into the proof other premises that Shields himself needs to defend.” There are several things wrong with this. First, Fr. Rooney seems to conflate the First Way in theSumma Theologiae with the second unmoved mover proof in the Summa contra Gentiles. I show in detail in the book how these two arguments are different. Only the latter proof shows, without further argumentation, that an immovable, everlasting mover is required. Secondly, saying that the mover must be exempt from potency for physical motion is not equivalent to saying that the mover is without potency altogether and thus pure act. Third, I do not deny that St. Thomas makes a further, metaphysical argument for the conclusion that God is pure act on the basis of the second unmoved mover argument in the Summa contra Gentiles, following Aristotle’s procedure in the Metaphysics. What I deny is that this argument is part of the unmoved mover argument, which is natural philosophical. Failure to observe this distinction turns the “more manifest” natural philosophical unmoved mover argument into a subtle metaphysical argument that only the wise can follow. This is contrary to Aquinas’ intention.

Fr. Rooney also objects to my claim that the origin of life requires an intelligent, supernatural cause. (Note that I make it clear in the book that once life exists it can evolve by purely natural causes. What is in question here is only the first production of a living organism on the early earth, roughly three and a half billion years ago.) He says that “even if we were to grant a principle of ‘proportionate causality,’ that alone does not allow us to conclude to intelligent creation. This is a non sequitur. For some medieval thinkers, too, the action of the celestial bodies could bring about spontaneous generation of living organisms from inanimate matter, without intelligent intervention.” (p. 670) The principle of “proportionate causality” is certainly a central principle in Aquinas’ own thought and it is a staple of contemporary Thomism, albeit one that is interpreted differently by different Thomists. But as far as the present issue is concerned, St. Thomas applies the principle of proportionate causality explicitly to the (putative) spontaneous generation of living organisms from non-living matter:

“As Augustine says, a living substance is superior to any non-living substance whatever. But a heavenly body is not a living substance, since it is inanimate. Therefore a sensitive soul, which is a principle of life, cannot be produced by its power. . . .

To the thirteenth objection it is to be said that even if a heavenly body is not living, nevertheless it acts by the power of the living substance by which it is moved, whether it be an angel or God.” Quaestiones Disputatae de Potentia Dei, q. 3, a. 11, obj. 13 & ad 13.

Aquinas holds that the heavenly bodies can only generate living organisms from putrifying matter because the heavenly bodies are being used instrumentally by their living, intelligent, immaterial movers. Otherwise they would be producing an effect disproportionate to their power, in violation of the principle of proportionate causality (which shows up all over Aquinas’ account here in De Potentia, q. 3.)

A modern Thomist has several options in dealing with this issue. He could hold, with Aquinas, that angels move heavenly bodies around and are responsible for orbital motion. I presume most of us Thomists don’t want to take this route. Another alternative is to water down the principle of proportionate causality so that it only requires causes with the power to produce the effect in question, not causes that equal or exceed their effect in ontological perfection. Then one could say that living organisms exist virtually in non-living causes. Several modern Thomists do take this route, but it has to be acknowledged that it is a serious departure from St. Thomas’ own thought. (That does not automatically make it false, but it will cause serious difficulty for Aquinas’ Treatise on the Divine Nature in the Summa Theologiae.) I find the principle of proportionate causality persuasive, however, on its classic interpretation as held by Aquinas himself. Causes must equal or exceed their effect.

That leaves two more options. The first is to say that God, by initiating the universe in a low-entropy condition fine-tuned for the production of life, has utilized the heavenly bodies as His instruments in the production of life. Non-living substances thus act in virtue of God’s power in bringing about life. The other option is to say that God or an angel intervened to initiate life on the early earth. I find this last option the more plausible one both in virtue of the scientific evidence and in itself. But the former option has merit as well.

This brings me to Fr. Rooney’s further point: “Shields’s own statement of the facts seems to indicate—as seems scientifically demonstrable—that at least some simple living organisms could be created simply by combining chemical constituents in the right way. Scientists have already successfully assembled single-celled organisms whose parts are mostly synthetic; there is no reason to believe there remains anything more than technical obstacles to the future achievement of organisms entirely synthetic.” I have no idea what Fr. Rooney is referring to by “Shields’s own statement of the facts seems to indicate . . .” The rest of his point here seems to me too facile. Does it rest on anything more than an act of scientific faith? Perhaps; Fr. Rooney clearly cannot, as he himself says, turn a review into a complete philosophical or scientific argument for a substantive claim. But it mischaracterizes matters to say that scientists have produced mostly synthetic organisms already. He may be referring the work of Craig Venter and his lab (although he does not say what he has in mind.) David Oderberg has already debunked the claims made in his regard: “Synthetic Life and the Bruteness of Immanent Causation,” in Aristotle on Metaphysics and Method, ed. Edward Feser, 206–35 (New York, NY: Palgrave Macmillan, 2013.) What Venter did was to stitch together small portions of a genome manually, then coax living cells to stitch together the small portions into a complete chromosome, and then replace the natural chromosome in another living cell with the quasi-artificial chromosome that his team put together. That is a far cry from a synthetic organism. It fits, rather, with the maxim omne vivens ex vivo. And does Fr. Rooney have anything to say in response to my thermodynamic account of living organisms? (To be clear: I do not claim that living organisms violate the second law of thermodynamics, but only that they utilize it to their advantage in a way that non-living things cannot.)

In fairness to Fr. Rooney, however, my discussion of living organisms and thermodynamics was not fully worked out in the book. I hope to develop it more fully in the future.

Once again, I thank Fr. Rooney for his overall appreciation of my work reconciling the unmoved mover argument and Thomistic natural philosophy in general with modern science.

Update: What the principle of proportionate causality requires for the production of the first life needs further clarification. Above I quoted obj. 13 of De Potentia q. 3, a. 11 and Aquinas’ reply to it. Obj. 14 anticipates Aquinas’ reply and pushes the objection further:

“But you will say that a heavenly body can be the cause of a sensitive soul insofar as it acts in the power (virtute) of the intellectual substance that moves it. But on the contrary, what is received in another is in it in the mode of the recipient and not in its own mode. If therefore the power (virtus) of an intellectual substance is received in a non-living heavenly body, it will not be there as a vital power (virtus vitalis) that can be the principle of life.

To the fourteenth objection it is to be said that the power of the living substance moving it remains in the heavenly body and in its motion not as a form that has complete being in nature, but in the mode of an intention as the power of art is in the artisan’s instrument.” QDP q. 3, a. 11, obj. 14 & ad 14.

Aquinas is appealing here to his distinction between natural existence (esse naturale) and intentional existence (esse intentionale) so central to his epistemology. The intelligible forms in the intellect and the sensible forms in the senses are the same forms that exist outside the soul in the objects known, but they exist with natural existence in the objects and with intentional existence in the soul; when cats are known the mind does not become a cat (that would be natural existence) but the mind refers to cats (which is intentional existence.) But Aquinas also holds that sensible forms with intentional existence exist in the medium between the object known and the knower. That is why the eyes succeed at seeing objects no matter where in the air the eyes are placed; the air is full of intentional forms.

Intentional existence can be thought of as a kind of informational existence. What Aquinas is saying in the quoted text is that the forms of living things must exist intentionally/informationally in the heavenly bodies if the heavenly bodies are to be instruments in the production of living things. So to develop the view that God produced living things on earth by fine-tuning the universe’s initial conditions, one would have to provide some kind of account of how the information needed to produce living organisms existed in the cosmos from the beginning, so as to satisfy the principle of proportionate causality. It is worth noting that many secular philosophers and scientists think of information as the opposite of entropy.

On the other hand, once living organisms already exist, they acquire and store and process information in their DNA. (See especially the work of the microbiologist James Shapiro.) Thus higher life forms can evolve naturally over time, insofar as many bits of information act together to provide the requisite causality for generating higher organisms. Thus evolution can proceed entirely by natural causes without violating the principle of proportionate causality.

Nova et Vetera has accepted my article “Five Ways, One Journey: Do Aquinas’ Five Ways Attempt to Prove the God of Classical Theism?” In the article I present a new reading of Aquinas’ Five Ways by attending carefully to each article in questions 2 & 3 of the Summa. The first two Ways only demonstrate that a god exists, whereas the Third, Fourth, and Fifth show what sort of thing a god is. The first three Ways constitute one extended, natural philosophical cosmological argument, even though each serves as a successful proof of a god’s existence all on its own as well. The conclusion of each Way is subsumed by the next Way, providing assurance that each concludes to the same being. Aquinas utilizes a weak, nominal definition of “god” as the criterion for a successful proof, namely “some being distinct from and superior to ordinary beings that governs as a first cause some realm in the universe.” He does not intend to prove the existence of the God of classical theism in his Five Ways nor does he intend to prove the existence of God as the self-subsistent act of existence, nor as pure act. He does not even intend to prove the existence of a single individual god. But the Fourth Way shows that only one kind of thing is a god; q. 3, a. 3 shows that there is not more than one individual god in a species; and q. 3, a. 5 shows that there is not more than one species of god. The God of classical theism is proved by the entirety of questions 2 & 3 taken together.

If you would like a copy, please email me.

Agustin Echavarria, in a recently published article in Theologica, defends classical theism from Joseph Schmid’s providential collapse objection (here and here.) He begins by commenting on my Thomistic response article (here and here). I appreciate his taking the time to read my work and for his respectful interaction with it. After an accurate presentation of the earlier parts of my paper, he has the following to say:

“Shields’ proposal is certainly suggestive. Moreover, if successful, it would end at the same time with both the problem of intentional collapse and the problem of providential collapse. One might even argue that it has more textual evidence in its favor in Aquinas’s texts than Shields himself provides. [He helpfully cites ST I q. 19 a. 2 ad 5; SCG I c. 79 n. 8; and SCG I c. 82 n. 12.] However, I have some doubts about whether this is the best way to approach the problem of providential collapse in particular. Mainly because this proposal seems to be contrary to what Tomaszewski calls the “modal indiscernibility thesis” (MIT). MIT is the idea that “if the doctrine of divine simplicity is true, then God in any possible world is really, intrinsically indiscernible from God in any other possible world” (Tomaszewski 2023, 238). To say that there are contingent relations in God established by His will implies that God establishes these relations of reason in some possible worlds and does not establish them in others; therefore, His will is not identical in every possible world with regard to these relations, which is contrary to MIT.” (Echavarria, p. 71)

The mentioned texts are certainly very helpful and I’m grateful that Echavarria points them out. In my paper, however, I maintain that “The one necessary act that [God] is identical with can contingently relate itself to the dog Fido as willing to create or as not willing to create, without any difference or contingency in God’s act.” (Shields, p. 86) “The act need not be different in itself to relate itself differently to creatures, as I have shown above.” (Shields, p. 87) “God does not need to be any different to have different relations to the same possible creature. . . . God’s one essence, with no difference in the act with which his essence is identical, can relate in different ways to possible creatures.” (Shields, p. 90)

I don’t think that my position violates Tomaszewski’s “Modal Indiscernability Thesis,” although I suppose that depends on precisely what Tomaszewski meant by it. But I claim that neither God nor His will (which are identical) would be any different intrinsically if He related differently to creatures, willing to create some that He has not in fact willed to create, and not willing to create some that He has in fact willed to create.

Echavarria seems to find this implausible; he has the following to say:

“This conclusion [that the Modal Indiscernability Thesis would be violated] is not avoided by saying, as Shields holds, that relations are not accidents or absolute ontological items in God, and so they are not intrinsic properties. As Shields himself admits, God’s contingent relations are different “ways” in which God’s will is determined with respect to certain possible creatures. Moreover, since they are relations “of reason,” their only possible ground must be in God’s will (rational appetite) itself, and not in something extrinsic to it. Hence, the existence of these relations implies by itself an intrinsic determination in God’s will, because they imply the intentional and intrinsic direction of the will toward certain possible creatures in particular, instead of others. Being contingent relations, this intrinsic determination of God’s will obtains in some possible worlds and not in others. Therefore, the very existence of these relations implies that the divine will is not intrinsically identical in every possible world.” (p. 71-72, emphasis added.)

I think that the italicized premise of the argument here is incorrect, and I gave an argument against it in my paper, p. 84-87. In the case of libertarian free-will, on pain of infinite regress, there has to be a first difference caused by the will, prior to which there is no other difference at all. A free will is such that without being any different intrinsically it can immediately produce different alternative effects. In God’s case, this very first difference is the relationship between His will and the possible creature. There need be no difference within God’s will causally prior to His relating differently to creatures, nor need any difference within God’s will accompany the difference in His relationship to creatures. As for intentionality, it is itself relational. God’s intentionality of creating this creature and not creating that creature just is the relation between Him and the creature. Echavarria did not choose to saying anything in response to this part of my argument, but in fairness to him his real target was Schmid and he spent the majority of his article developing his own response to Schmid.

Echavarria’s own response raises concerns for me. He makes some helpful points in response to Schmid, in particular that he overreached in claiming that the set of God’s possible effects would be utterly without restriction on the doctrine of divine simplicity. But Echevarria seems to deny God’s total, immediate, and particular providence. St. Thomas certainly thinks that God has such total, particular, and detailed providential control over everything in the universe. (See, for example, ST I, q. 22, a. 2 & 3; q. 23, a. 4.) I am worried that Echevarria’s defense of classical theism is not very classical. However, he indicates that the question of intentionality and intentional collapse is crucial here, and that he deals with God’s intentionality in a forthcoming article. It’s possible that this will clarify his position in such a way that it preserves the particular divine providence essential to classical theism. I am interested to see what he has to say in any case.

On November 14th, 2025, I delivered a public lecture at Wyoming Catholic College titled “The Heavens Declare the Glory of God: Modern Physics and an Ancient Cosmological Argument.” The lecture summarizes and extends the second part of my book, Nature and Nature’s God. I defend the Thomistic cosmological argument for an unmoved mover in light of modern physics. A recording of the lecture and Q & A is currently available on youtube.