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A Modal Argument Against Naturalism from Transcendentals

For any argument against naturalism, we are going to have to specify the sort of naturalism we are discussing.  Here, my target is a rather broad notion of metaphysical naturalism.  Let’s define the notion in the following way: naturalism is the thesis that reality is exhausted by the natural.[1]  This is, admittedly not an informative definition (and somewhat circular), but it will do the job of being relatively broad for this argument, but not so vacuous as to be uninteresting.  Many contemporary naturalists would assent to the definition, and I, being Catholic, believe that naturalism, so defined, is false.

P1. Naturalism is true just in case “natural” is greater than and includes the combined extensions of terms that name each and every one of the categories into which being may be divided.[2]

P2. “Natural” is greater than and includes the combined extensions of terms that name each and every one of the categories into which being may be divided just in case “natural” is a transcendental that is convertible with “being”.

P3. All terms that are transcendental that are convertible with “being” are necessarily transcendentals that are convertible with “being”.

P4. If naturalism is true, naturalism is contingently true.

P5. If naturalism is contingently true, it is false that “natural” is necessarily a transcendental that is convertible with being.

C1. Therefore, naturalism is false.

The argument is a reductio, as the premises lead to an obvious contradiction if one assumes naturalism is true (i.e. “natural” is necessarily a transcendental that is convertible with “being” and it is false that “natural” is necessarily a transcendental that is convertible with “being”). Given the definition of “transcendental” and the plausibility of P3-P5, naturalism cannot be the case.

There are a few ways the naturalist may object (and why I think they are inadequate objections):

Objection 1: “Natural” is not a transcendental.

Reply to 1: If “natural” is not a transcendental, as defined extensionally, then it is not exhaustive of reality.  Let’s say that reality is composed of everything, all beings.  If “natural” doesn’t exhaust all beings, then there are beings that are not natural.  That, to me, is sufficient to falsify metaphysical naturalism.  So this is not a very good move to make, though it may be a knee-jerk move to make in response to the argument.

Objection 2: There are no transcendentals.  The idea that res, unum, aliquid, bonum, et verum or any other supposed transcendental like “beauty” is convertible with being is a quaint notion from an outmoded era of philosophy and theology when people drank in far too many Hellenistic notions.

Reply to 2: Fine, you dislike older ideas.  But the extensional definition of transcendentals are still on the table and there is no reason to think that we cannot categorize being, or devise a notion of a term that is universal.  After all, as I suggested in response to the first objection, to say that “natural” exhaust reality is to say something about the universality of “natural” and that its extension would be as broad as “being” or “reality”.  So, it sounds odd to object to there being transcendental terms when naturalism, so defined, depends on it.  Ah, but “naturalism” could be defined in other ways.  That’s true, but those sorts of “naturalisms” are not the target of this argument.  Moreover, I am not too sure that I am opposed to a form of metaphysical naturalism that is too timid to claim that “natural” exhausts “being”.

Objection 3: P3 is false.  There is no reason to think that if some term is convertible with “being”, then it is necessarily so.  It might be contingently convertible with being, especially if “transcendental” is only being defined extensionally.  That is, the transcendentals could merely happen to be convertible with “being”.

Reply to 3: It would seem, then, that we have two sorts of transcendentals: contingent transcendentals that happen to be convertible with “being” and necessary transcendentals that are necessarily convertible with “being”.  So, for instance, if God were actually to exist, there would be a sense in which res, unum, aliquid, bonum, et verum could be applied to God.  But, presumably, if God were to exist, “natural” could not apply to Him.  In other words, were there super-natural beings, “natural” would have a smaller extension than “being” and “natural” would cease to be a transcendental.  Yet, the other named transcendentals are not like this.  No matter what possibilia comes to be, the transcendentals would remain what they are.  It’s just that the actualization of the possibilia means that the actuality is res, unum, aliquid, bonum, et verum.  It seems, then, that the naturalist would be committed to the thesis that “natural” is convertible with “actual”, i.e. everything is actual if and only if it is natural.  But “actuality” is not a transcendental.  Rather, one can divide the various categories of being into act and potency.  In other words, actuality has a smaller extension than any given category and, a fortiori the combined extensions of all the categories of being.  Now the naturalist might quibble and say that any potential or possibility of the non-natural, or supernatural, is itself natural.  But this is not to address the question of whether “natural” is extensive with all potentials and possibilities, but just the actualities in which those potentials and possibilities obtain.

Another issue is that it is rather question-begging to demand that “natural” is one instance of a “contingent transcendental” convertible with being given what actually happens to exist.  Is there another such transcendental? Why are all the other transcendentals necessary and remain transcendentals no matter what happens to be in the world.

Objection 4: P4 is false.  Metaphysical worldviews, if true, are necessarily true.  Thus, if metaphysical naturalism is true, then it is somehow necessarily true.

Reply to 4: This is a rather strong position to take.  For it not only posits that supernatural entities, like souls, and gods, do not exist.  It posits that they cannot exist for metaphysical or broadly logical reasons.  It is not clear to me why this must be the case, and there seems to be good reason to think this is false.  1) Even if it is not supposed that the Anselmian God is metaphysically possible (from which, some would argue, His existence could be demonstrated), a less than maximally great or perfect divinity is plausibly metaphysically possible.  That is, a being that would sufficiently falsify naturalism, even if it is not morally perfect, omniscient, or omnipotent, could exist.  What’s more, if metaphysical naturalism is metaphysically necessary, then it would satisfy the Leibnizian question “why is there something rather than nothing” in much the way classical theists think God satisfies this question.  The classical theist says that God is metaphysically necessary, so not anything existing is impossible.  But the metaphysical naturalist doesn’t seem to make the same move.  Faced with the radical contingency of reality, the metaphysical naturalist usually doesn’t say that since metaphysical naturalism is metaphysical necessary, there must be at least one natural thing in existence.  If nothing were in existence, then nothing natural would exist.  Now a particularly impish naturalist might suggest that, were there nothing in existence, metaphysical naturalism would be true.  That is, one natural configuration of the world is “there not being anything”.  But if there were nothing, it wouldn’t be the case that “natural” exhausts reality.  “Natural” would not be predicated at all.  It would no more “exhaust” reality than “supernatural”.  So there not being anything is not compatible with metaphysical naturalism being true.  So if metaphysical naturalism is necessary, nothing is intrinsically impossible.  Yet, we have no reason to think that if naturalism is true, some natural thing or other must exist.

Objection 5: Okay, metaphysical naturalism is only contingently true, but “natural” is necessarily a transcendental convertible with being anyways.  In other words, P5 is false.

Reply to 5: Well, if there is no possible world where “natural” fails to exhaust “being”, then metaphysical naturalism would be true in every possible world.  Metaphysical naturalism cannot be contingent while it be necessary the everything is natural.  That just is to claim that metaphysical naturalism is true in every possible world (a strong claim to make).

In Sum: If I were a naturalist, I think I would try to argue that some transcendentals are contingent. I don’t think the argument would be very convincing, for the reasons I mentioned.  After that, I think I would want to argue that metaphysical naturalism is necessary.  Remember, it is not enough to simply say that metaphysical naturalism could be necessary. If all of the other premises of my argument are correct, and one wants to maintain metaphysical naturalism as true, one would have to admit that the only way it could be true is if it is metaphysically necessary.  However, I don’t see any good reason to think metaphysical naturalism is metaphysically necessary for the reasons I’ve outlined above.  So, it seems to me that, since “natural” is not a transcendental of “being”, metaphysical naturalism is false.

[1] Papineau, David, “Naturalism”, The Stanford Encyclopedia of Philosophy (Spring 2009 Edition), Edward N. Zalta (ed.), URL = <>.

[2] This is based on an extensional definition of transcendentals offered by Jorge J.E. Gracia. See Jorge J.E. Gracia, 1992, “The Transcendentals in the Middle Ages: An Introduction,” Topoi 11(2): 113–120. Also Wouter Goris and Jan Aertsen, “Medieval Theories of Transcendentals”, The Stanford Encyclopedia of Philosophy (Summer 2013 Edition), Edward N. Zalta (ed.), URL = <>

An Argument Against Naturalism from the Desire to Know

Aristotle begins his Metaphysics by saying something about human nature, “All men by nature desire to know” (Met. A, 980b22).  If it is by our nature, we might be so bold as to count it among our essential properties.  But, what does it mean to “desire”?  And in particular, what does it mean to desire knowledge? Socrates provides the following account of “desire” in Plato’s Symposium:

Then this is what it is to love something which is not at hand, which the lover does not have: it is to desire the preservation of what he now has in time to come, so that he will have it then… So such a man or anyone else who has a desire desires what is not at hand and not present, what he does not have, and what he is not, and that of which he is in need; for such are the objects of desire and love… (Symposium 200d-e).

If this is so, to desire knowledge is to love something that is not at hand.  It is to want and to keep knowledge.  This also means that to have and to hold knowledge satisfies the desire for it.  Such a situation is reflected in a quote that I saw posted on the blog of a friend and colleague.  The quote is from an article by Lorraine Daston.  The quote is as follows:

Therein lies the paradox of wonder: it is the beginning of inquiry (Descartes remarks that people deficient in wonder “are ordinarily quite ignorant”), but the end of inquiry also puts an end to wonder. The marvel that stopped us in our tracks—an aurora borealis, cognate words in languages separated by continents and centuries, the peacock’s tail—becomes only an apparent marvel once explained. Aesthetic appreciation may linger (it is no accident that the vernacular descendants of the Latin word for wonder, admiratio, convey esteem), but composure has returned. We are delighted but no longer discombobulated; what was once an earthquake of the soul is subdued into an agreeable frisson. At least within the classical philosophical tradition, from Aristotle to Descartes (and arguably beyond, to Adam Smith and even to Kant), this negative correlation between wonder and explanation is strong and tenacious. Explanation lies at the heart of the distinction between marvels and miracles in the Latin Christian tradition. What is the difference? Thomas Aquinas answers: marvels (mirabilia) are inexplicable to most but not all people (e.g. the eclipse that transfixes the ignorant peasant but not the learned astronomer); miracles (miracula) are inexplicable to everyone. Wonder is a barometer of ignorance: the learned experience it rarely; God, never. Wonder is not only a peculiarly human passion; it is also one that, at least on this account, underscores the limits of human knowledge. The more we know, the less we wonder.

Daston’s thesis is actually moves in quite the opposite.  She holds that our understanding of “wonder” has evolved and adapted such that wonder is not snuffed out by knowledge, but is generated by knowledge.  Not to disregard her thesis, but I do want to consider this more ancient notion of wonder for a moment.  As Aristotle tells us that:

…it is owing to their wonder that men both now being and at first began to philosophize; they wondered originally at the obvious difficulties, then advanced little by little and stated difficulties about the greater matters, e.g. about the phenomena of the moon and those of the sun and the stars, and about the genesis of the universe.  And a man who is puzzled and wonders thinks himself ignorant (whence even the lover of myth is in a sense a lover of wisdom, for myth is composed of wonders); therefore since they philosophized in order to escape from ignorance, evidently they were pursuing science in order to know, and not for any utilitarian end (Met. A, 982b11-22).

Now if naturalism is true, then the world may be filled with marvels, perhaps very inexplicable marvels like consciousness, but it is not filled with that which is, in principle, inexplicable for us.  This does not mean that, on naturalism, reality could ever be fully disenchanted.  There seems to be practical limitations that would prevent us from explaining everything.  At the same time, it does mean that the relationship between reality and our minds is such that it is merely accidental that we have the desire to know.  We could, in principle, uncover all of the marvels that exist and satisfy this desire.  In snuffing it out, the desire would cease to exist in us.  So actually having the desire for knowledge would be accidental if everything in existence were knowable for us.  But, if the actuality of desiring knowledge is an essential feature of the human intellect, then there must be some sense in which, in principle, reality is not fully knowable or explicable.  This would be true if there were true supernatural miracles and mysteries. The argument would be as follows:

1.  All humans actually desire knowledge essentially. [Premise]

2. If naturalism is true, then the actuality of human desire for knowledge is accidental. [Premise]

3. If the actuality of human desire for knowledge is accidental, then it is not the case that all humans actually desire knowledge essentially. [Premise]

4. Therefore, it is not the case that naturalism is true.

Now there are a few ways the naturalist could object:

Objection 1: Though naturalism is true, there are some natural mysteries that are unknowable, intractable, or inexplicable in principle. For instance, we may not be able to know or understand why there is something rather than nothing. We might not be able to know if there is a multiverse, or what occurred before the big bang. We might not be able to explain consciousness. We might not be able to fully explain those soft sciences that involve human behavior (owing to human freedom, or chaos, or indeterminism).

Reply to 1: It seems to me that if there are per se mysterious features of reality, there is no reason to be a naturalist. I take naturalism to be the claim that all of reality can be accounted for by the natural sciences. If certain aspects of reality are not merely really difficult to account for by natural scientific methodology, but intrinsically and essentially beyond the scope of the natural sciences, then I would say that metaphysical naturalism is a failure (or just a vacuous metaphysical position).

Objection 2: One could bite the bullet and say that humans don’t actually desire knowledge in an essential way. It is merely an accidental property of our mental constitution. Perhaps the capacity to desire knowledge is essential to humans, but not the actuality.

Reply to 2: This seems like a more powerful objection than the first. Humans satisfy desires all the time. In fact, there is a famous argument from desire put forth by C.S. Lewis, which argues that all natural desires have an object in reality that can satisfy their desires. So it might seem that the existence of the humanly unknowable or inexplicable contradicts this premise. However, the argument from desire does not hold that all desires are satisfied. The hungry child who is a victim of famine may never get the food that satisfies her, though such food exists. There may be knowledge that exists, say in the mind of an omniscient God, that we desire, but can never possess (due to our natural limitations). So the fact that we cannot completely satisfy our desire for knowledge, and that all natural desires have corresponding objects, does not mean that there is nothing to know when it comes to the truly miraculous or mysterious.

Now one might say that nothing really is truly miraculous or mysterious. We can, in principle, explain everything naturally, we are just limited by time and other pressing needs. And one might even be willing to grant that humans possess the capacity to desire wisdom in an essential way (the potential/power to desire knowledge), but that capacity can be fulfilled in the following way: we actually desire knowledge when we are actually ignorant and potentially in a state of knowledge. When we change to a state of potentially desiring knowledge, we are actually in a state of knowledge and are potentially ignorant. We could, in principle, be in a state of potentially desiring all knowledge, if we can be in a state of actually knowing all things (potentially ignorant). So this objection amounts to the claim that we humans have the capacity for omniscience essentially (perhaps as a collective and through various mediums of storing knowledge).

I find this response too strong. I don’t think any naturalist would want to hold it either. Ultimately, I think the idea that humans will always be in some actual state of desire for knowledge rests on a certain intuition about the relationship between the human capacity for knowledge and the way reality is. My intuition is that not everything can be known by us. And this, to me, stands in the way of metaphysical naturalism. For what else is the naturalist claiming than that reality falls completely under the genus “natural”. And so reality can be completely defined and comprehended by our intellects. If this is not the naturalist’s claim, then I am not sure what naturalism is supposed to be (at times I suspect it really is just the denial of souls and God, but that is not a positive metaphysical position).

One might point out that we don’t always actually desire knowledge (small babies, the sleeping, etc.). Furthermore, some desire knowledge more than others. Doesn’t this indicate that, while the capacity to desire knowledge may be essential, the actuality of that desire can change and is accidental to our circumstances and personal dispositions. A response might be to consider Aristotle’s musical man. In a sense, one can argue that all humans, sleeping, and even the very young, have a natural desire to know is a first actuality insofar as one has an intellect that is always deprived of knowledge that it desires to have. The second actuality might be something like the active awareness of that desire, which motivates one’s investigations. Even the very young explore their world with their eyes, hands, and mouth. So, I don’t think it is the case that even the very young escape this state.

An Argument from the Regularity of Nature to the Falsity of Metaphysical Naturalism

I find the following argument compelling:

P1. If it is both the case that something has an explanation and that explanation is natural, then it has an explanation that depends on the actuality of the regularity of nature.
P2. If something is contingent, it is not the case that it has an explanation that depends upon the actuality of itself.
P3. All things that are actual are possible.
P4. All things that are possible, and not necessary, are contingent.
P5. All things that are contingent have an explanation.
P6. The regularity of nature is actual.
P7. The regularity of nature is not necessary.
P8. If something has an explanation and it is not the case that the explanation is natural, then metaphysical naturalism is false.
C1. The regularity of nature is possible (from P3 and P6).
C2. The regularity of nature is contingent (from P4, P7, and C1).
C3. The regularity of nature has explanation (from P5 and C2).
C4. It is not the case that the regularity of nature has an explanation that depends upon the actuality of itself (from P2 and C2).
C5. It is not both the case that the regularity of nature has an explanation and that explanation is natural (from P1 and C4).
C6. It is not the case that the explanation of the regularity of nature is natural (from C3 and C5).
C7. Therefore, metaphysical naturalism is false (from P8, C3, and C6).

An Argument Against Naturalism from Abstract Objects

Some naturalists, like Quine, feel compelled to admit abstract objects, like numbers, sets, and propositions, into their ontology. But I’ve always had the sense that abstract objects are incompatible with naturalism. Here I will lay out some premises about abstract objects and naturalism that appear fairly intuitive to me. I will then represent those premises in logical notation, and demonstrate that they do, indeed, serve as a defeater for naturalism.

1. If a thing1 is natural then it is possibly not the case that there exists a thing2 where thing2 is natural and identical to thing1.

In other words, if a think is natural, then it possibly doesn’t exist.

2. There exists some proposition such that necessarily that proposition is true.

For example, the mathematical proposition ‘2 + 3 = 5’ is necessarily true and cannot be false.

3. For all propositions, necessarily, if a proposition is true, then there exists some thing1 such that thing1 is abstract and thing1 is identical to that proposition.

This is just to say that it is necessary that if a proposition is true, then it is an existing abstract object. After all, it would seem odd to predicate a truth-value to a proposition, but deny that said proposition doesn’t exist.

4. If there exists a proposition that is necessarily true, and everything is natural, then for all proposition, necessarily, if there exists a thing1 that is an abstract object identical to that proposition, then there exists a natural thing2 identical to that proposition.

I defend this premise on the grounds that, if a proposition is natural, then in every world where it obtains, it obtains as a natural proposition. That is, if ‘natural’ is predicated of a proposition, it is essentially predicated of it, which is to say that in every world where that proposition exists, it exists as a natural object.

From these four premise, we can conclude that naturalism, which I take to be the claim that everything is natural, is false.

The deduction is as follows:

Nx – x is natural
Tp – p is true
Ax – x is an abstract object

1. (∀x){Nx ⊃ ♢~(∃y)[Ny & (y=x)]} (premise)
2. (∃p)☐Tp (premise)
3. (∀p)☐[(Tp ⊃ (∃x)(Ax & (x=p))] (premise)
4. (∃p)(☐Tp & (∀x)Nx) ⊃ (∀p)☐{(∃x)[Ax & (x=p)] ⊃ (∃y)[Ny & (y=p)]} (premise)
5. (∀p)☐{(∃x)[Ax & (x=p)] ⊃ (∃y)[Ny & (y=p)]} (IP)
6. ☐Tu (2 EI)
7. ☐[(Tu ⊃ (∃x)(Ax & (x=u))] (3 UI)
8. ☐(∃x)(Ax & (x=u) (6,7 MMP)
9. ☐{(∃x)[Ax & (x=u)] ⊃ (∃y)[Ny & (y=u)]} (5, UI)
10. ☐(∃y)[Ny & (y=u)] (8,9 MMP)
11. (∃y)[Ny & (y=u)] (10 NE)
12. Nv & (v=u) (11 EI)
13. Nv ⊃ ♢~(∃y)[Ny & (y=v)] (1 UI)
14. Nv (12 Simp)
15. ♢~(∃y)[Ny & (y=v)] (13,14 MP)
16. (v=u) (12 Simp)
17. ♢~(∃y)[Ny & (y=u)] (15,16 ID)
18. ~☐(∃y)[Ny & (y=u)] (17 MN)
19. ☐(∃y)[Ny & (y=u)] & ~☐(∃y)[Ny & (y=u)] (10,18 Conj)
20. ~(∀p)☐{(∃x)[Ax & (x=p)] ⊃ (∃y)[Ny & (y=p)]} (IP 5-19)
21. ~(∃p)(☐Tp & (∀x)Nx) (4,20 MT)
22. (∀p)~(☐Tp & (∀x)Nx) (21, QN)
23. ☐Tu (2 EI)
24. ~(☐Tu & (∀x)Nx) (22 UI)
25. ~☐Tu ∨ ~(∀x)Nx (24 DeM)
26. ~~☐Tu (23 DN)
27. ~(∀x)Nx (25,26 DS)
28. (∃x)~Nx (27 QN)

Line 28 is our conclusion, namely that something exists that is not natural. I take this to be incompatible with naturalism. Therefore, I take the existence of abstract objects, like propositions, to be a defeater for naturalism. I suspect that the naturalist will take issue with one or more of the premises, but at a cost. Likely (4) will require the most defending. Again, (4) says that, given naturalism and the existence of necessary truths, it is necessarily the case that if a proposition exists as an abstract object, it will exist as a natural object. If one denies this, then it would seem possible that an abstract object be natural and possibly not natural. But then in what way is it the same sort of thing? It seems odd to me that a proposition is a natural thing in this world, but a non-natural thing in other possible worlds. For it seems to me that the property of being natural is an essential property. If something is natural, it is necessary that it is natural. Thus, if naturalism is true, then all abstract objects are natural and essentially natural. But our argument shows, by indirect proof, that it is possible for there to exist an abstract object that is not natural. Giving up on (4) entails that ‘natural’ is non-essential to some things, and I find that to be implausible.

(My thanks to Skepticism First on Twitter, who dialogued with me on this argument and pushed me in some new directions)

Knowability and a Dilemma for the Naturalist

In a previous post I argued that the knowability of truth entails an omniscient mind. But the whole argument is predicated on the knowability principle, KP, which states that truth can be known. But, who would defend such a position? “Only theists” one might suspect. As it turns out, KP follows upon some versions of anti-realism and idealism.1 Of course, in light of the paradox, many anti-realists have modified their form of anti-realism so that it does not fall prey to “paradox”.2 Whether these more subtle anti-realists escape the knowability paradox is still a matter hotly debated (Brogaard 2009).

The (naïve?) anti-realist is not the only one who commits herself to KP. Verificationists, like the logical positivists of yesteryear, also hold to KP, since meaning is predicated on analytic or empirical verifiability.3 If KP is expressed in the slogan “To be true is to be provable”, one can still faintly hear Ayer and his acolytes chanting their implicit consent to KP. Ironically, so long as the positivists admit that there is a maximally big conjunctive truth, they would have to concede that an omniscient mind exists. How embarrassing!

Perhaps less surprising, though also worthy of note, is that Aquinas, a metaphysical realist, would also be a proponent of KP:

There is nothing, however, that the divine intellect does not actually know, and nothing that the human intellect does not know potentially, for the agent intellect is said to be that “by which we make all things knowable,” and the possible intellect, as that “by which we become all things.” For this reason, one can place in the definition of a true thing its actually being seen by the divine intellect, but not its being seen by a human intellect, except potentially, as is clear from our earlier discussion (De Veritate Q. 1,A.2).4

I mention this because the literature on the knowability paradox seems to equate KP with antirealism. But, as Aquinas proves, there is no reason why KP should be restricted to anti-realism.5 It is clear that for Aquinas all things are known to some mind, i.e. God, and knowable to all other minds. Of course my non-theistic interlocutor should hardly be moved by any of this, unless she were to embrace the particularities of Thomistic psychology while eschewing his metaphysics. I suspect dodos would be less rare.

I would also like to consider some objections to KP. Some of my interlocutors have already countered my claims that all truths are knowable by referencing the Münchhausen trilemma or Gödel’s incompleteness theorems. Münchhausen trilemma offers us three options, each of which appear to be untoward for the tenability of epistemology. The trilemma runs as follows:

1. Justifications for some knowledge must be justified, ad infinitum, which abandons foundationalism.
2. Justifications are eventually circular, which means that knowledge is question begging.
3. Justifications are not sought for some truths, which abandons justification arbitrarily.

But before we despair, its readily apparent that the trilemma is answered by various epistemologies. Infinitists take the first horn. Infinitism does not abandon knowability, but argues that knowledge may be justified by an infinite chain. I wouldn’t personally take this horn, but it seems to me that many, especially non-theists, claim to have no problem with infinite regresses. For justification can emerge out of the infinite chain of reasoning much like an effect can arise out of an infinite sea of prior causes. So, if my non-theistic interlocutors reject knowability on the basis of this trilemma, I might ask them to reconsider the force of Thomas’s Five Ways.

The second horn is accepted by coherentists. They reject the charge that these, so called, loops of justification beg the question. Rather, they see knowledge in a holistic way. Beliefs fit within a reinforcing and consistent web. The literature is rife with defenses of this position, so it is at least a plausible alternative to utter skepticism.

Furthermore, it seems to me that the Reformed Epistemology argues that justifications are unnecessary in knowing some truths, i.e. those truths that are properly basic. But this is not to embrace the third horn, since there are specific conditions offered by which a belief can be considered properly basic. Hence, stopping points are not inherently arbitrary, or in violation of some PSR. Even the foundationalist typically will concede that the law of non-contradiction needs no support. But RE allows for stopping points that extend beyond mere logical principles and analytic truths, and so extends the foundation of knowledge out much further.

So the Münchhausen trilemma does not force us into some form of Pyrrhonism, nor does it explicitly assert that some truths are unknowable. It merely forces us to think more clearly about epistemology, which is a good thing. So in my assessment, the Münchhausen trilemma is not a good reason to reject KP.

As for Gödel’s incompleteness theorems, while they do seem to suggest that truth transcends proof, it should be noted that “proof” must be understood within the context of an axiomatic system, and does not mean justification or warrant in some broader epistemological sense. It is for this reason that we cannot simply concede to the highly controversial thesis that the results of the incompleteness theorems are applicable to human minds, or any other minds for that matter. In fact, Lucas and Penrose have argued that Gödel’s theorems are an indication that the mind is not a Turing-Machine, that human intelligence is not restricted to axiomatic proofs, and that truths that no machine could know, can be known to us. If so, AI will never be analogous to human intelligence. In sum, I do not think it is compelling to say that Gödel’s incompleteness theorems count against KP without the additional support of the premise that all minds are functionally equivalent to Turing machines.

So, I have suggested that there are philosophical defenders of the knowability thesis, both realists and anti-realists, theists and atheists. Also, I have defended KP against the two main objections raised by my interlocutors thus far. Still, are there any good reasons to endorse KP? I have no deductive argument or a priori argument to offer. I’m an optimist, and I’d like to think that all truths can be known in principle. Absent a defeater, I think there are good inductive reasons for accepting KP. They can be summarized as follows:

1. No specific instance of a truth that one might point to is unknowable.
2. Therefore, all truths are knowable.

(1) is equivalent to the fact that all specific instances of truth that one might point to are knowable. In other words, KP is continually confirmed, and counterexamples are not forthcoming, and never will be forthcoming. For to confirm the truth of a counterexample would require that we know that something unknowable is true, which is a contradiction. If induction may be used to support a principle, then it certainly offers abundant evidence in support of KP.

One last point, and this is for the naturalists:

Suppose the metaphysical naturalist were to reject the knowability principle in an attempt to escape my argument for an omniscient mind. The rejection of the knowability principle would entail that there are some truths that cannot be known, verified, etc. by our best, or even ideal, natural sciences. If a truth is defined as natural insofar as it comports with and can be subjected to analysis and empirical verification by a natural science, it follows that there would some non-natural truths. This raises an interesting dilemma for the metaphysical naturalist:

1. Either all truths are knowable, or not all truths are knowable. (LEM)
2. If all truths are knowable, then an omniscient mind exists. (see this post for proof)
3. If not all truths are knowable, then some truths cannot be verified by the natural sciences even in principle.
4. If some truths cannot be verified by the natural sciences in principle, then metaphysical naturalism is false.
5. Therefore, either an omniscient mind exists, or metaphysical naturalism is false.

I think both disjuncts are true, but it seems that we are forced to pick one! And its on odd metaphysical naturalist who admits that there is an omniscient mind.

1 B. Brogaard & J. Salerno, 2009. “Fitch’s Paradox of Knowability”, The Stanford Encyclopedia of Philosophy (Winter 2012 Edition), Edward N. Zalta (ed.), URL = <;.

2 S.A. Rasmussen. 2009. “The Paradox of Knowability and the Mapping Objection”. In New Essays on the Knowability Paradox. Ed. J. Salerno. New York: Oxford University Press. 53-54

3 J. Beall “Knowability and Possible Epistemic Oddities”. In New Essays on the Knowability Paradox. Ed. J. Salerno. New York: Oxford University Press. 113-4

4 Thomas Aquinas. 1952. Questiones Disputatae de Veritate. Trans. Robert W. Mulligan, S.J.Chicago: Henry Regnery Company. Ed. Joseph Kenny, O.P. Accessed July 20, 2013. URL = <;

5 Plantinga seems to identify Thomas as a theistic anti-realist, since Thomas thinks that truth would not exist without minds. However, Thomas is careful to note that “truth”, though found primarily in the intellect, is secondarily found in things. It is for this reason that I reject Plantinga’s assessment. See A. Plantinga. 1982. Proceedings and Addresses of the American Philosophical Association, Vol. 56, No. 1. 47-70