So physical possibility is a subset of metaphysical possibility, which is a subset of logical possibility. Anything physically possible is metaphysically possible, and anything metaphysically possible is logically possible. Although those three categories are all commonly used in the philosophy literature, only two of them are meaningful. Metaphysical modality, as a concept, cannot be rescued from its fundamental flaws:
1. Any proposition using physical or logical modality has a truth value, because unlike a proposition using metaphysical modality, one can meaningfully define physical and logical modality and how they are known.
Defining logical and physical modality is easy enough. Any proposition p is logically impossible just in case p entails some contradiction(s). p is logically necessary just in case denying p entails some contradiction(s). The same applies to physical possibility/necessity, except with p contradicting the laws of physics instead of p contradicting itself. But it is unclear what metaphysical possibility and necessity mean. Perhaps p is metaphysically impossible just in case p contradicts some "law of metaphysics," but it is unclear (1) what a "law of metaphysics" is, and (2) how one would discover any "law of metaphysics."
Contrast the other kinds of modality for both (1) and (2). A "law of logic" is a deductive rule determining what kinds of propositions are conceptually incoherent according to the syntax of thought, as I describe while refuting the Transcendental Argument for God. One can discover "laws of logic" by conceptual analysis in several ways: If a true conclusion always follows from multiple true premises according to the deductive rule R, then R is a law of logic. Also, if one can conceive/visualize a situation where R is false, then R is not a law of logic.
Now contrast physical modality. The "laws of physics" are predictive generalizations about what anyone has ever observed. They are discovered through empirical observation. I described that in more detail while refuting Gerald Schroeder's cosmological argument. But again, for any "laws of metaphysics," it is unclear (1) what such laws are and (2) how one would discover any such laws.
Dr. Craig and Saul Kripke both claimed that metaphysical modality must be meaningfully coherent by giving examples of statements that appear metaphysically possible or metaphysically necessary. Yet one can simply call those statements logically possible but physically impossible without entailing any absurdities or other problems.
Unless and until someone provides criteria for defining what metaphysical modality is, and how to discover it, I cannot call any propositions of metaphysical modality true or false. I can only call propositions of logical or physical modality true or false. Note that this does not apply to metaphysical propositions regarding actuality: For a proposition about metaphysical actuality to be true is just for that proposition to describe reality/existence, and for that proposition to be false is just for it to fail to describe reality/existence. One can discover propositions about metaphysical actuality (among other ways) through the implications of the most likely scientific theories. So I do not claim to achieve "the elimination of metaphysics," as many twentieth-century logical positivists like Rudolf Carnap claimed. I only claim to eliminate metaphysical modality.
Contrast the other kinds of modality for both (1) and (2). A "law of logic" is a deductive rule determining what kinds of propositions are conceptually incoherent according to the syntax of thought, as I describe while refuting the Transcendental Argument for God. One can discover "laws of logic" by conceptual analysis in several ways: If a true conclusion always follows from multiple true premises according to the deductive rule R, then R is a law of logic. Also, if one can conceive/visualize a situation where R is false, then R is not a law of logic.
Now contrast physical modality. The "laws of physics" are predictive generalizations about what anyone has ever observed. They are discovered through empirical observation. I described that in more detail while refuting Gerald Schroeder's cosmological argument. But again, for any "laws of metaphysics," it is unclear (1) what such laws are and (2) how one would discover any such laws.
Dr. Craig and Saul Kripke both claimed that metaphysical modality must be meaningfully coherent by giving examples of statements that appear metaphysically possible or metaphysically necessary. Yet one can simply call those statements logically possible but physically impossible without entailing any absurdities or other problems.
Unless and until someone provides criteria for defining what metaphysical modality is, and how to discover it, I cannot call any propositions of metaphysical modality true or false. I can only call propositions of logical or physical modality true or false. Note that this does not apply to metaphysical propositions regarding actuality: For a proposition about metaphysical actuality to be true is just for that proposition to describe reality/existence, and for that proposition to be false is just for it to fail to describe reality/existence. One can discover propositions about metaphysical actuality (among other ways) through the implications of the most likely scientific theories. So I do not claim to achieve "the elimination of metaphysics," as many twentieth-century logical positivists like Rudolf Carnap claimed. I only claim to eliminate metaphysical modality.
2. Some have attempted to define metaphysical possibility as the ability to be actualized. However, the 'ability' to be actualized is just the possibility of being actualized. This definition tries to define possibility in terms of itself, making the definition circular and therefore meaningless.
Dr. Craig defined "metaphysically impossible" as "incapable of actualization." On its face, this seems like a meaningfully coherent definition of metaphysical modality: something is metaphysically possible if and only if it is capable of actualization, and metaphysically necessary unless it is capable of not being actualized. But this definition relies on the idea of "capability," which is simply another word for "possibility." The phrase "X is incapable of doing Y" simply means "X cannot possibly do Y." So Craig tried to define "metaphysically impossible" as "impossible to actualize." No one can define a term using that same term, though, because then one would have to already know the term's meaning to define the term’s meaning. Either the sense of "possible" in Craig's definition is metaphysical possibility, making his definition circular; or it is another kind of possibility, in which case metaphysical possibility can be wholly reduced to that kind. Since Craig is unlikely to endorse reducing metaphysical modality to another kind of modality, his attempted definition of metaphysical modality is circular and therefore meaningless. Metaphysical modality is a meaningless concept that ought to be jettisoned from philosophical discourse.
The same problem plagues the Stanford Encyclopedia of Philosophy. In its page on “The Epistemology of Modality,” the SEP says that “metaphysical possibilities are the logical possibilities that are also allowed by the natures of all of the things that could have existed.” A metaphysical impossibility, per this definition, contradicts the essential nature of some thing(s) in the set of “all of the things that could have existed.” Even without objecting to the idea of essential natures, one can notice that the definition is circular: The phrase “things that could have existed” is simply another way to say “things that possibly exist.” Since possibility cannot be defined in terms of itself, the SEP either defined metaphysical modality in terms of some other kind of modality or failed to define metaphysical modality at all.
Discovering that no one has defined metaphysical modality felt like discovering that the emperor has no clothes, especially because not even Wikipedia has found a meaningful definition of metaphysical modality. In its page on "subjunctive" (i.e., modal) "possibility," Wikipedia lists four types of possibility: logical, nomological, [3]Note 3. Nomological possibility is another name for empirical or physical possibility. temporal, and metaphysical. It provides meaningfully coherent definitions of the first three, but not metaphysical possibility. The page mentions two things about metaphysical possibility: "Metaphysical possibility is either equivalent to logical possibility or narrower than it," and "Some philosophers have held that discovered identities such as Kripke's 'Water is H2O' are metaphysically necessary but not logically necessary." Neither of these points specifies (1) what metaphysical possibility actually is, or (2) how one would know whether any particular thing is metaphysically possible or not. It is difficult to stress exactly how unusual Wikipedia's omission here is, because the first two sentences in each paragraph describing every other kind of possibility include a precise definition. This unusual factor is because metaphysical modality is meaningless.
At this point I have become desperate for someone — anyone — to give me a meaningfully coherent definition of metaphysical modality. Toni Kannisto’s excellent overview of modal metaphysics on Quora fell into the same mistake as Dr. Craig by defining metaphysical possibility in terms of some unspecified other possibility. Kannisto described metaphysical possibility as "what could exist (also called real possibility), i.e. what we could encounter in the world or what could affect us." But every one of these defines metaphysical possibility in terms of the word "could" which, like the word "(in)capable," is simply another word for possibility. So Kannisto’s attempted definitions of metaphysical possibility are simply "what possibly exists, i.e. what we possibly encounter in the world or what possibly affects us." Again, these circular definitions are meaningless.
The same problem plagues the Stanford Encyclopedia of Philosophy. In its page on “The Epistemology of Modality,” the SEP says that “metaphysical possibilities are the logical possibilities that are also allowed by the natures of all of the things that could have existed.” A metaphysical impossibility, per this definition, contradicts the essential nature of some thing(s) in the set of “all of the things that could have existed.” Even without objecting to the idea of essential natures, one can notice that the definition is circular: The phrase “things that could have existed” is simply another way to say “things that possibly exist.” Since possibility cannot be defined in terms of itself, the SEP either defined metaphysical modality in terms of some other kind of modality or failed to define metaphysical modality at all.
Discovering that no one has defined metaphysical modality felt like discovering that the emperor has no clothes, especially because not even Wikipedia has found a meaningful definition of metaphysical modality. In its page on "subjunctive" (i.e., modal) "possibility," Wikipedia lists four types of possibility: logical, nomological, [3]Note 3. Nomological possibility is another name for empirical or physical possibility. temporal, and metaphysical. It provides meaningfully coherent definitions of the first three, but not metaphysical possibility. The page mentions two things about metaphysical possibility: "Metaphysical possibility is either equivalent to logical possibility or narrower than it," and "Some philosophers have held that discovered identities such as Kripke's 'Water is H2O' are metaphysically necessary but not logically necessary." Neither of these points specifies (1) what metaphysical possibility actually is, or (2) how one would know whether any particular thing is metaphysically possible or not. It is difficult to stress exactly how unusual Wikipedia's omission here is, because the first two sentences in each paragraph describing every other kind of possibility include a precise definition. This unusual factor is because metaphysical modality is meaningless.
At this point I have become desperate for someone — anyone — to give me a meaningfully coherent definition of metaphysical modality. Toni Kannisto’s excellent overview of modal metaphysics on Quora fell into the same mistake as Dr. Craig by defining metaphysical possibility in terms of some unspecified other possibility. Kannisto described metaphysical possibility as "what could exist (also called real possibility), i.e. what we could encounter in the world or what could affect us." But every one of these defines metaphysical possibility in terms of the word "could" which, like the word "(in)capable," is simply another word for possibility. So Kannisto’s attempted definitions of metaphysical possibility are simply "what possibly exists, i.e. what we possibly encounter in the world or what possibly affects us." Again, these circular definitions are meaningless.
3. Metaphysical modal claims cannot be known through 'intellectual intuition,' 'divine wisdom,' 'conceptual analysis,' 'transcendental argumentation,' or 'thought-experiments.'
Toni Kannisto also briefly reviewed all of the different proposed epistemologies of metaphysical modality, and why they have been criticized. Philosophers defending metaphysical modal claims have usually claimed to know these claims by "Intellectual intuition or light of reason," "Divine wisdom," "Conceptual analysis," "Transcendental argumentation," or "Thought-experiments." Conceptual analysis is "logical analysis combined with certain meanings given to some fundamental concepts." Transcendental argumentation is "determination of the necessary conditions of some fundamental concepts known to latch onto reality (e.g. experience or knowledge)." Using thought experiments can allegedly let one "determin[e] what is possible to conceive of or imagine to be the case." Consider each in turn.
Kannisto admitted that the first two categories, "Intellectual intuition" and "Divine wisdom," are "Not very satisfactory" and "Not very philosophical" respectively. In the first case, as I show elsewhere, one cannot distinguish one's "intellectual intuition" from mere psychological intuition — that is, mental associative reasoning processes. Since associative reasoning is only reliable for predicting experiences within a familiar and stable environment, intuition cannot justifiably be used to discover such fundamental truths as metaphysical necessity. The same problem applies to relying on "thought experiments," which are all designed to export intuitions from the familiar context where they were reliable into a new, unfamiliar context where they are no longer reliable. Claiming that one gains metaphysical modal knowledge by "divine wisdom" is circular in any apologetics context, where the existence of divine wisdom is in question.
The only remaining ways to define metaphysical modality are through "Transcendental argumentation" or "Conceptual analysis." Drawing on Immanuel Kant, Kannisto defined "transcendental argumentation" as "tak[ing] some undeniable fact of our existence, for instance that we perceive, and maps out the necessary conditions for this to be possible." Yet this collapses into epistemic possibility. For any proposition P,
Finally, Kannisto defined "conceptual analysis" as "logical analysis combined with certain meanings given to some fundamental concepts" which "can determine a set of metaphysical possibilities." Although Kannisto called it "[p]erhaps the most popular among these methods," he did not explain what "logical analysis," which "certain meanings," or which "fundamental concepts" a metaphysical modal claim would use. Kannisto said that "Spinoza provides perhaps the quintessential example of this method." If so, then I doubt it will lead anywhere coherent, at least considering the Stanford Encyclopedia of Philosophy's page blasting the confusion of Spinozan modal metaphysics:
There may be some clear and compelling way to know the truth value of a metaphysical modal claim through conceptual analysis. But until I encounter a definition of metaphysical modality and criteria to evaluate metaphysical modal claims, I cannot help but call metaphysical modality meaningless.
Kannisto admitted that the first two categories, "Intellectual intuition" and "Divine wisdom," are "Not very satisfactory" and "Not very philosophical" respectively. In the first case, as I show elsewhere, one cannot distinguish one's "intellectual intuition" from mere psychological intuition — that is, mental associative reasoning processes. Since associative reasoning is only reliable for predicting experiences within a familiar and stable environment, intuition cannot justifiably be used to discover such fundamental truths as metaphysical necessity. The same problem applies to relying on "thought experiments," which are all designed to export intuitions from the familiar context where they were reliable into a new, unfamiliar context where they are no longer reliable. Claiming that one gains metaphysical modal knowledge by "divine wisdom" is circular in any apologetics context, where the existence of divine wisdom is in question.
The only remaining ways to define metaphysical modality are through "Transcendental argumentation" or "Conceptual analysis." Drawing on Immanuel Kant, Kannisto defined "transcendental argumentation" as "tak[ing] some undeniable fact of our existence, for instance that we perceive, and maps out the necessary conditions for this to be possible." Yet this collapses into epistemic possibility. For any proposition P,
- P is epistemically necessary just in case P is known to be true.
- P is epistemically impossible just in case P is known to be false.
- P is epistemically possible otherwise.
- If P is a necessary condition for some "undeniable fact of our existence," then that "undeniable fact" entails P. Since that fact is known, so is P, making P "epistemically necessary."
- If P is not necessary to explain an "undeniable fact," and P does not contradict any "undeniable facts," then one does not know whether P is true or false, making P "epistemically possible."
- If P contradicts some "undeniable fact," then P is known to be false, making it "epistemically impossible."
Finally, Kannisto defined "conceptual analysis" as "logical analysis combined with certain meanings given to some fundamental concepts" which "can determine a set of metaphysical possibilities." Although Kannisto called it "[p]erhaps the most popular among these methods," he did not explain what "logical analysis," which "certain meanings," or which "fundamental concepts" a metaphysical modal claim would use. Kannisto said that "Spinoza provides perhaps the quintessential example of this method." If so, then I doubt it will lead anywhere coherent, at least considering the Stanford Encyclopedia of Philosophy's page blasting the confusion of Spinozan modal metaphysics:
"Spinoza’s views on necessity and possibility, which he claimed were the “principal foundation” of his Ethics (Ep75), have been less than well received by his readers, to put it mildly. From Spinoza’s contemporaries to our own, readers of the Ethics have denounced Spinoza’s views on modality as metaphysically confused at best, ethically nihilistic at worst. However, expressing matters this way implies that there is a consensus about Spinoza’s metaphysics of modality and that interpreters differ only to the extent to which they distance themselves from his outrageous position. A cursory reading of certain passages of the Ethics supports the belief that, if Spinoza is clear anywhere, it is surely in his views of necessity and contingency ... [but] considerable disagreement has emerged about Spinoza’s modal commitments. Much of this disagreement stems from larger interpretive disagreements about Spinoza’s metaphysics."It would be intellectually lazy and dishonest to dismiss the idea of defining metaphysical possibility using "conceptual analysis" simply because Spinoza apparently used it poorly. Yet from what I have seen, this kind of "conceptual analysis" appears to be a euphemism for asserting sweeping, oversimplified slogans like "everything has an explanation of its existence" or "nothing comes from nothing" without justification — and denying that these slogans need justification.
There may be some clear and compelling way to know the truth value of a metaphysical modal claim through conceptual analysis. But until I encounter a definition of metaphysical modality and criteria to evaluate metaphysical modal claims, I cannot help but call metaphysical modality meaningless.