Mathematical fallacy

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In mathematics, certain kinds of mistaken proof are often exhibited, and sometimes collected, as illustrations of a concept of mathematical fallacy. There is a distinction between a simple mistake and a mathematical fallacy in a proof: a mistake in a proof leads to an invalid proof just in the same way, but in the best-known examples of mathematical fallacies, there is some concealment in the presentation of the proof. For example, the reason validity fails may be a division by zero that is hidden by algebraic notation. There is a certain quality of the mathematical fallacy: as typically presented, it leads not only to an absurd result, but does so in a crafty or clever way. Therefore, these fallacies, for pedagogic reasons, usually take the form of spurious proofs of obvious contradictions. Although the proofs are flawed, the errors, usually by design, are comparatively subtle, or designed to show that certain steps are conditional, and are not applicable in the cases that are the exceptions to the rules.

The traditional way of presenting a mathematical fallacy is to give an invalid step of deduction mixed in with valid steps, so that the meaning of fallacy is here slightly different from the logical fallacy. The latter applies normally to a form of argument that is not a genuine rule of logic, where the problematic mathematical step is typically a correct rule applied with a tacit wrong assumption. Beyond pedagogy, the resolution of a fallacy can lead to deeper insights into a subject (such as the introduction of Pasch's axiom of Euclidean geometry and the five colour theorem of graph theory). Pseudaria, an ancient lost book of false proofs, is attributed to Euclid.

Mathematical fallacies exist in many branches of mathematics. In elementary algebra, typical examples may involve a step where division by zero is performed, where a root is incorrectly extracted or, more generally, where different values of a multiple valued function are equated. Well-known fallacies also exist in elementary Euclidean geometry and calculus.

Howlers

Examples exist of mathematically correct results derived by incorrect lines of reasoning. Such an argument, however true the conclusion, is mathematically invalid and is commonly known as a howler. For example, the calculation (anomalous cancellation):

${\displaystyle {\frac {16}{64}}={\frac {16\!\!\!/}{6\!\!\!/4}}={\frac {1}{4}}.}$

Although the conclusion ${\displaystyle \textstyle {\frac {16}{64}}={\frac {1}{4}}}$ is correct, there is a fallacious, invalid cancellation in the middle step. Another classical example of a howler is proving the Cayley-Hamilton theorem by simply substituting the scalar variables of the characteristic polynomial by the matrix.

Bogus proofs, calculations, or derivations constructed to produce a correct result in spite of incorrect logic or operations were termed "howlers" by Maxwell. Outside the field of mathematics the term howler has various meanings, generally less specific.

Division by zero

The division-by-zero fallacy has many variants. The following example uses division by zero to "prove" that ${\displaystyle 2=1}$, but can be modified to prove that any number equals any other number.

1. Let ${\displaystyle a}$ and ${\displaystyle b}$ be equal, non-zero quantities

   ${\displaystyle a=b}$

2. Multiply by ${\displaystyle a}$

   ${\displaystyle a^{2}=ab}$

3. Subtract ${\displaystyle b^{2}}$

   ${\displaystyle a^{2}-b^{2}=ab-b^{2}}$

4. Factor both sides: the left factors as a difference of squares, the right is factored by extracting ${\displaystyle b}$ from both terms

   ${\displaystyle (a-b)(a+b)=b(a-b)}$

5. Divide out ${\displaystyle (a-b)}$

   ${\displaystyle a+b=b}$

6. Observing that ${\displaystyle a=b}$

   ${\displaystyle b+b=b}$

7. Combine like terms on the left

   ${\displaystyle 2b=b}$

8. Divide by the non-zero ${\displaystyle b}$

   ${\displaystyle 2=1}$

Q.E.D.

The fallacy is in line 5: the progression from line 4 to line 5 involves division by a − b, which is zero since a equals b. Since division by zero is undefined, the argument is invalid.

Multivalued functions

Many functions do not have a unique inverse. For instance, while squaring a number gives a unique value, there are two possible square roots of a positive number. The square root is multivalued. One value can be chosen by convention as the principal value; in the case of the square root the non-negative value is the principal value, but there is no guarantee that the square root given as the principal value of the square of a number will be equal to the original number; e.g. the principal square root of the square of −2 is 2.

Calculus

Calculus as the mathematical study of infinitesimal change and limits can lead to mathematical fallacies if the properties of integrals and differentials are ignored. For instance, a naive use of integration by parts can be used to give a false proof that 0 = 1. Letting ${\displaystyle \textstyle u={\frac {1}{\log x}}}$ and ${\displaystyle \textstyle dv={\frac {dx}{x}}}$, we may write:

${\displaystyle \int {\frac {1}{x\,\log x}}\,dx=1+\int {\frac {1}{x\,\log x}}\,dx}$

after which the antiderivatives may be cancelled yielding 0 = 1. The problem is that antiderivatives are only defined up to a constant and shifting them by 1 or indeed any number is allowed. The error really comes to light when we introduce arbitrary integration limits a and b.

${\displaystyle \int _{a}^{b}{\frac {1}{x\,\log x}}\,dx=1|_{a}^{b}+\int _{a}^{b}{\frac {1}{x\,\log x}}\,dx=0+\int _{a}^{b}{\frac {1}{x\,\log x}}\,dx=\int _{a}^{b}{\frac {1}{x\,\log x}}\,dx}$

Since the difference between two values of a constant function vanishes, the same definite integral appears on both sides of the equation.

Power and root

Fallacies involving disregarding the rules of elementary arithmetic through an incorrect manipulation of the radical.

Positive and negative roots

Care must be taken when taking the square root of both sides of an equality. Failing to do so results in a proof of

${\displaystyle 5=4.}$

Proof:

Start from

${\displaystyle -20=-20}$

Write this as

${\displaystyle 25-45=16-36}$

Rewrite as

${\displaystyle 5^{2}-5\times 9=4^{2}-4\times 9}$

Add ${\displaystyle 81/4}$ on both sides:

${\displaystyle 5^{2}-5\times 9+81/4=4^{2}-4\times 9+81/4}$

These are perfect squares:

${\displaystyle (5-9/2)^{2}=(4-9/2)^{2}}$

Take the square root of both sides:

${\displaystyle 5-9/2=4-9/2}$

Add ${\displaystyle 9/2}$ on both sides:

${\displaystyle 5=4}$

Q.E.D.

The fallacy is in the second to last line, where the square root of both sides is taken: a² = b² only implies a = b if a and b have the same sign, which is not the case here. In this case it implies a = –b and should read 5-9/2 = -(4-9/2), which, by adding 9/2 on both sides, correctly reduces to 5 = 5.

As another example of the danger of taking the square root of both sides of an equation, consider the fundamental identity

${\displaystyle \cos ^{2}x=1-\sin ^{2}x}$

which holds as a consequence of the Pythagorean theorem. Then, by taking a square root,

${\displaystyle \cos x={\sqrt {1-\sin ^{2}x}}}$

so that

${\displaystyle 1+\cos x=1+{\sqrt {1-\sin ^{2}x}}.}$

But evaluating this when x = π implies

${\displaystyle 1-1=1+{\sqrt {1-0}}}$

or

${\displaystyle 0=2}$

which is incorrect.

The error in each of these examples fundamentally lies in the fact that any equation of the form

${\displaystyle x^{2}=a^{2}}$

has two solutions, provided a ≠ 0,

${\displaystyle x=\pm a}$

and it is essential to check which of these solutions is relevant to the problem at hand. In the above fallacy, the square root that allowed the second equation to be deduced from the first is valid only when cos x is positive. In particular, when x is set to π, the second equation is rendered invalid.

Squaring both sides of an equation

When both sides of an equation are squared, sometimes solutions are induced that were not present in the original equation.

An example of this kind of fallacy, is the following invalid proof that ${\displaystyle -2=2}$:

Let

${\displaystyle x=-2.}$

Squaring gives

${\displaystyle x^{2}=4}$

whereupon taking a square root implies

${\displaystyle x={\sqrt {4}}=2,}$

so that

${\displaystyle x=-2=2,}$

which is absurd.

When the square root was extracted, it was the negative root −2, rather than the positive root, that was relevant for the particular solution in the problem.

Square roots of negative numbers

Invalid proofs utilizing powers and roots are often of the following kind:

${\displaystyle 1={\sqrt {1}}={\sqrt {(-1)(-1)}}={\sqrt {-1}}{\sqrt {-1}}=i\cdot i=-1.}$

The fallacy is that the rule ${\displaystyle \textstyle {\sqrt {xy}}={\sqrt {x}}{\sqrt {y}}}$ is generally valid only if both x and y are positive (when dealing with real numbers), which is not the case here.

Alternatively, imaginary roots are obfuscated in the following:

${\displaystyle i={\sqrt {-1}}=(-1)^{\frac {2}{4}}=((-1)^{2})^{\frac {1}{4}}=1^{\frac {1}{4}}=1}$

The error here lies in the last equality, where we are ignoring the other fourth roots of 1, which are −1, i and −i (where i is the imaginary unit). Since we have squared our figure and then taken roots, we cannot always assume that all the roots will be correct. So the correct fourth roots are i and −i, which are the imaginary numbers defined to square to −1.

Complex exponents

When a number is raised to a complex power, the result is not uniquely defined. If this property is not recognized, then errors such as the following can result:

${\displaystyle {\begin{aligned}e^{2\pi i}&=1\\(e^{2\pi i})^{i}&=1^{i}\\e^{-2\pi }&=1\\\end{aligned}}}$

The error here is that the rule of multiplying exponents as when going to the third line does not apply unmodified with complex exponents, even if when putting both sides to the power i only the principal value is chosen. When treated as multivalued functions, both sides produce the same set of values, being {e^2πn | n ∈ ℤ}.

Geometry

Many mathematical fallacies in geometry arise from using in an additive equality involving oriented quantities (such adding vectors along a given line or adding oriented angles in the plane) a valid identity, but which fixes only the absolute value of (one of) these quantities. This quantity is then incorporated into the equation with the wrong orientation, so as to produce an absurd conclusion. This wrong orientation is usually suggested implicitly by supplying an imprecise diagram of the situation, where relative positions of points or lines are chosen in a way that is actually impossible under the hypotheses of the argument, but non-obviously so. Such a fallacy is easy to expose by drawing a precise picture of the situation, in which some relative positions will be different from those in the provided diagram. In order to avoid such fallacies, a correct geometric argument using addition or subtraction of distances or angles should always prove that quantities are being incorporated with their correct orientation.

Fallacy of the isosceles triangle

The fallacy of the isosceles triangle, from (Maxwell 1959, Chapter II, § 1), purports to show that every triangle is isosceles, meaning that two sides of the triangle are congruent. This fallacy has been attributed to Lewis Carroll.

Given a triangle △ABC, prove that AB = AC:

1. Draw a line bisecting ∠A
2. Draw the perpendicular bisector of segment BC, which bisects BC at a point D
3. Let these two lines meet at a point O.
4. Draw line OR perpendicular to AB, line OQ perpendicular to AC
5. Draw lines OB and OC
6. By AAS, △RAO ≅ △QAO (∠ORA = ∠OQA = 90°; ∠RAO = ∠QAO; AO = AO (common side))
7. By RHS, △ROB ≅ △QOC (∠BRO = ∠CQO = 90°; BO = OC (hypotenuse); RO = OQ (leg))
8. Thus, AR = AQ, RB = QC, and AB = AR + RB = AQ + QC = AC

Q.E.D.

As a corollary, one can show that all triangles are equilateral, by showing that AB = BC and AC = BC in the same way.

The error in the proof is the assumption in the diagram that the point O is inside the triangle. In fact, O always lies at the circumcircle of the △ABC (except for isosceles and equilateral triangles where AO and OD coincide). Furthermore, it can be shown that, if AB is longer than AC, then R will lie within AB, while Q will lie outside of AC (and vice versa). (Any diagram drawn with sufficiently accurate instruments will verify the above two facts.) Because of this, AB is still AR + RB, but AC is actually AQ − QC; and thus the lengths are not necessarily the same.

Proof by induction

There exist several fallacious proofs by induction in which one of the components, basis case or inductive step, is incorrect. Intuitively, proofs by induction work by arguing that, if a statement is true in one case, it is true in the next case, and hence by repeatedly applying this it can be shown to be true for all cases. This "proof" shows that all horses are the same colour.

1. Let us say that any group of N horses is all of the same colour.
2. If we remove a horse from the group, we have a group of N - 1 horses of the same colour. If we add another horse, we have another group of N horses. By our previous assumption, all the horses are of the same colour in this new group, since it is a group of N horses.
3. Thus we have constructed two groups of N horses all of the same colour, with N - 1 horses in common. Since these two groups have some horses in common, the two groups must be of the same colour as each other.
4. Therefore, combining all the horses used, we have a group of N + 1 horses of the same colour.
5. Thus if any N horses are all the same colour, any N + 1 horses are the same colour.
6. This is clearly true for N = 1 (i.e. one horse is a group where all the horses are the same colour). Thus, by induction, N horses are the same colour for any positive integer N. i.e. all horses are the same colour.

The fallacy in this proof arises in line 3. For N = 1, the two groups of horses have N − 1 = 0 horses in common, and thus are not necessarily the same colour as each other, so the group of N + 1 = 2 horses is not necessarily all of the same colour. The implication "Every N horses are of the same colour, then N+1 horses are of the same colour" works for any N greater than one, but fails to be true when N = 1. The basis case is correct, but the induction step has a fundamental flaw. If we were additionally given the fact that any two horses shared the same colour, we could correctly induct from the base case of N = 2.

Omnipotence paradox

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Detail depicting Averroes, who addressed the omnipotence paradox in the 12th century, from the 14th-century Triunfo de Santo Tomás by Andrea da Firenze (di Bonaiuto)

The omnipotence paradox is a family of paradoxes that arise with some understandings of the term 'omnipotent'. The paradox arises, for example, if one assumes that an omnipotent being has no limits and is capable of realizing any outcome, even logically contradictory ideas such as creating square circles. A no-limits understanding of omnipotence such as this has been rejected by theologians from Thomas Aquinas to contemporary philosophers of religion, such as Alvin Plantinga. Atheological arguments based on the omnipotence paradox are sometimes described as evidence for atheism, though Christian theologians and philosophers, such as Norman Geisler and William Lane Craig, contend that a no-limits understanding of omnipotence is not relevant to orthodox Christian theology. Other possible resolutions to the paradox hinge on the definition of omnipotence applied and the nature of God regarding this application and whether or not omnipotence is directed toward God himself or outward toward his external surroundings.

The omnipotence paradox has medieval origins, dating at least to the 12th century. It was addressed by Averroës and later by Thomas Aquinas. Pseudo-Dionysius the Areopagite (before 532) has a predecessor version of the paradox, asking whether it is possible for God to "deny himself".

The most well-known version of the omnipotence paradox is the so-called paradox of the stone: "Could God create a stone so heavy that even He could not lift it?" This phrasing of the omnipotence paradox is vulnerable to objections based on the physical nature of gravity, such as how the weight of an object depends on what the local gravitational field is. Alternative statements of the paradox that do not involve such difficulties include "If given the axioms of Euclidean geometry, can an omnipotent being create a triangle whose angles do not add up to 180 degrees?" and "Can God create a prison so secure that he cannot escape from it?".

Overview

A common modern version of the omnipotence paradox is expressed in the question: "Can [an omnipotent being] create a stone so heavy that it cannot lift it?" This question generates a dilemma. The being can either create a stone it cannot lift, or it cannot create a stone it cannot lift. If the being can create a stone that it cannot lift, then it seems that it can cease to be omnipotent. If the being cannot create a stone it cannot lift, then it seems it is already not omnipotent.

A related issue is whether the concept of 'logically possible' is different for a world in which omnipotence exists than a world in which omnipotence does not exist.

The dilemma of omnipotence is similar to another classic paradox—the irresistible force paradox: What would happen if an irresistible force were to meet an immovable object? One response to this paradox is to disallow its formulation, by saying that if a force is irresistible, then by definition there is no immovable object; or conversely, if an immovable object exists, then by definition no force can be irresistible. Some claim that the only way out of this paradox is if the irresistible force and immovable object never meet. But this is not a way out, because an object cannot in principle be immovable if a force exists that can in principle move it, regardless of whether the force and the object actually meet.

Types of omnipotence

Peter Geach describes and rejects four levels of omnipotence. He also defines and defends a lesser notion of the "almightiness" of God.

1. "Y is absolutely omnipotent" means that "Y" can do anything that can be expressed in a string of words even if it is self-contradictory: "Y" is not bound by the laws of logic."
2. "Y is omnipotent" means "Y can do X" is true if and only if X is a logically consistent description of a state of affairs. This position was once advocated by Thomas Aquinas. This definition of omnipotence solves some of the paradoxes associated with omnipotence, but some modern formulations of the paradox still work against this definition. Let X = "to make something that its maker cannot lift." As Mavrodes points out there is nothing logically contradictory about this. A man could, for example, make a boat that he could not lift.
3. "Y is omnipotent" means "Y can do X" is true if and only if "Y does X" is logically consistent. Here the idea is to exclude actions that are inconsistent for Y to do but might be consistent for others. Again sometimes it looks as if Aquinas takes this position. Here Mavrodes' worry about X= "to make something its maker cannot lift" is no longer a problem, because "God does X" is not logically consistent. However, this account may still have problems with moral issues like X = "tells a lie" or temporal issues like X = "brings it about that Rome was never founded."
4. "Y is omnipotent" means whenever "Y will bring about X" is logically possible, then "Y can bring about X" is true. This sense, also does not allow the paradox of omnipotence to arise, and unlike definition #3 avoids any temporal worries about whether or not an omnipotent being could change the past. However, Geach criticizes even this sense of omnipotence as misunderstanding the nature of God's promises.
5. "Y is almighty" means that Y is not just more powerful than any creature; no creature can compete with Y in power, even unsuccessfully. In this account nothing like the omnipotence paradox arises, but perhaps that is because God is not taken to be in any sense omnipotent. On the other hand, Anselm of Canterbury seems to think that almightiness is one of the things that make God count as omnipotent.

Augustine of Hippo in his City of God writes "God is called omnipotent on account of His doing what He wills" and thus proposes the definition that "Y is omnipotent" means "If Y wishes to do X then Y can and does do X".

The notion of omnipotence can also be applied to an entity in different ways. An essentially omnipotent being is an entity that is necessarily omnipotent. In contrast, an accidentally omnipotent being is an entity that can be omnipotent for a temporary period of time, and then becomes non-omnipotent. The omnipotence paradox can be applied to each type of being differently.

Some Philosophers, such as René Descartes, argue that God is absolutely omnipotent. In addition, some philosophers have considered the assumption that a being is either omnipotent or non-omnipotent to be a false dilemma, as it neglects the possibility of varying degrees of omnipotence. Some modern approaches to the problem have involved semantic debates over whether language—and therefore philosophy—can meaningfully address the concept of omnipotence itself.

Proposed answers

Omnipotence doesn't mean breaking the laws of logic

A common response from Christian philosophers, such as Norman Geisler or William Lane Craig, is that the paradox assumes a wrong definition of omnipotence. Omnipotence, they say, does not mean that God can do anything at all but, rather, that he can do anything that's possible according to his nature. The distinction is important. God cannot perform logical absurdities; he cannot, for instance, make 1+1=3. Likewise, God cannot make a being greater than himself because he is, by definition, the greatest possible being. God is limited in his actions to his nature. The Bible supports this, they assert, in passages such as Hebrews 6:18, which says it is "impossible for God to lie."

Another common response to the omnipotence paradox is to try to define omnipotence to mean something weaker than absolute omnipotence, such as definition 3 or 4 above. The paradox can be resolved by simply stipulating that omnipotence does not require that the being have abilities that are logically impossible, but only be able to do anything that conforms to the laws of logic. A good example of a modern defender of this line of reasoning is George Mavrodes. Essentially, Mavrodes argues that it is no limitation on a being's omnipotence to say that it cannot make a round square. Such a "task" is termed by him a "pseudo-task" as it is self-contradictory and inherently nonsense. Harry Frankfurt—following from Descartes—has responded to this solution with a proposal of his own: that God can create a stone impossible to lift and also lift said stone

For why should God not be able to perform the task in question? To be sure, it is a task—the task of lifting a stone which He cannot lift—whose description is self-contradictory. But if God is supposed capable of performing one task whose description is self-contradictory—that of creating the problematic stone in the first place—why should He not be supposed capable of performing another—that of lifting the stone? After all, is there any greater trick in performing two logically impossible tasks than there is in performing one?

If a being is accidentally omnipotent, it can resolve the paradox by creating a stone it cannot lift, thereby becoming non-omnipotent. Unlike essentially omnipotent entities, it is possible for an accidentally omnipotent being to be non-omnipotent. This raises the question, however, of whether or not the being was ever truly omnipotent, or just capable of great power. On the other hand, the ability to voluntarily give up great power is often thought of as central to the notion of the Christian Incarnation.

If a being is essentially omnipotent, then it can also resolve the paradox (as long as we take omnipotence not to require absolute omnipotence). The omnipotent being is essentially omnipotent, and therefore it is impossible for it to be non-omnipotent. Further, the omnipotent being can do what is logically impossible—just like the accidentally omnipotent—and have no limitations except the inability to become non-omnipotent. The omnipotent being cannot create a stone it cannot lift.

The omnipotent being cannot create such a stone because its power is equal to itself—thus, removing the omnipotence, for there can only be one omnipotent being, but it nevertheless retains its omnipotence. This solution works even with definition 2—as long as we also know the being is essentially omnipotent rather than accidentally so. However, it is possible for non-omnipotent beings to compromise their own powers, which presents the paradox that non-omnipotent beings can do something (to themselves) which an essentially omnipotent being cannot do (to itself). This was essentially the position Augustine of Hippo took in his The City of God:

For He is called omnipotent on account of His doing what He wills, not on account of His suffering what He wills not; for if that should befall Him, He would by no means be omnipotent. Wherefore, He cannot do some things for the very reason that He is omnipotent.

Thus Augustine argued that God could not do anything or create any situation that would, in effect, make God not God.

In a 1955 article in the philosophy journal Mind, J. L. Mackie tried to resolve the paradox by distinguishing between first-order omnipotence (unlimited power to act) and second-order omnipotence (unlimited power to determine what powers to act things shall have). An omnipotent being with both first and second-order omnipotence at a particular time might restrict its own power to act and, henceforth, cease to be omnipotent in either sense. There has been considerable philosophical dispute since Mackie, as to the best way to formulate the paradox of omnipotence in formal logic.

God and logic:

Although the most common translation of the noun "Logos" is "Word" other translations have been used. Gordon Clark (1902–1985), a Calvinist theologian and expert on pre-Socratic philosophy, famously translated Logos as "Logic": "In the beginning was the Logic, and the Logic was with God and the Logic was God." He meant to imply by this translation that the laws of logic were derived from God and formed part of Creation, and were therefore not a secular principle imposed on the Christian world view.
God obeys the laws of logic because God is eternally logical in the same way that God does not perform evil actions because God is eternally good. So, God, by nature logical and unable to violate the laws of logic, cannot make a boulder so heavy he cannot lift it because that would violate the law of non contradiction by creating an immovable object and an unstoppable force.
This raises the question, similar to the Euthyphro Dilemma, of where this law of logic, which God is bound to obey, comes from. According to these theologians (Norman Geisler and William Lane Craig), this law is not a law above God that he assents to but, rather, logic is an eternal part of God's nature, like his omniscience or omnibenevolence.

Paradox is meaningless: the question is sophistry, meaning it makes grammatical sense, but has no intelligible meaning

Another common response is that since God is supposedly omnipotent, the phrase "could not lift" does not make sense and the paradox is meaningless. This may mean that the complexity involved in rightly understanding omnipotence—contra all the logical details involved in misunderstanding it—is a function of the fact that omnipotence, like infinity, is perceived at all by contrasting reference to those complex and variable things, which it is not. An alternative meaning, however, is that a non-corporeal God cannot lift anything, but can raise it (a linguistic pedantry)—or to use the beliefs of Hindus (that there is one God, who can be manifest as several different beings) that whilst it is possible for God to do all things, it is not possible for all his incarnations to do them. As such, God could create a stone so heavy that, in one incarnation, he couldn't lift it, yet could do something that an incarnation that could lift the stone could not.

The lifting a rock paradox (Can God lift a stone larger than he can carry?) uses human characteristics to cover up the main skeletal structure of the question. With these assumptions made, two arguments can stem from it: 

1. Lifting covers up the definition of translation, which means moving something from one point in space to another. With this in mind, the real question would be, "Can God move a rock from one location in space to another that is larger than possible?" For the rock to be unable to move from one space to another, it would have to be larger than space itself. However, it is impossible for a rock to be larger than space, as space always adjusts itself to cover the space of the rock. If the supposed rock was out of space-time dimension, then the question would not make sense—because it would be impossible to move an object from one location in space to another if there is no space to begin with, meaning the faulting is with the logic of the question and not God's capabilities.
2. The words, "Lift a Stone" are used instead to substitute capability. With this in mind, essentially the question is asking if God is incapable, so the real question would be, "Is God capable of being incapable?" If God is capable of being incapable, it means that He is incapable, because He has the potential to not be able to do something. Conversely, if God is incapable of being incapable, then the two inabilities cancel each other out, making God have the capability to do something.

The act of killing oneself is not applicable to an omnipotent being, since, despite that such an act does involve some power, it also involves a lack of power: the human person who can kill himself is already not indestructible, and, in fact, every agent constituting his environment is more powerful in some ways than himself. In other words, all non-omnipotent agents are concretely synthetic: constructed as contingencies of other, smaller, agents, meaning that they, unlike an omnipotent agent, logically can exist not only in multiple instantiation (by being constructed out of the more basic agents they are made of), but are each bound to a different location in space contra transcendent omnipresence. 

Thomas Aquinas asserts that the paradox arises from a misunderstanding of omnipotence. He maintains that inherent contradictions and logical impossibilities do not fall under the omnipotence of God. J. L Cowan sees this paradox as a reason to reject the concept of 'absolute' omnipotence, while others, such as René Descartes, argue that God is absolutely omnipotent, despite the problem.

C. S. Lewis argues that when talking about omnipotence, referencing "a rock so heavy that God cannot lift it" is nonsense just as much as referencing "a square circle"; that it is not logically coherent in terms of power to think that omnipotence includes the power to do the logically impossible. So asking "Can God create a rock so heavy that even he cannot lift it?" is just as much nonsense as asking "Can God draw a square circle?" The logical contradiction here being God's simultaneous ability and disability in lifting the rock: the statement "God can lift this rock" must have a truth value of either true or false, it cannot possess both. This is justified by observing that for the omnipotent agent to create such a stone, it must already be more powerful than itself: such a stone is too heavy for the omnipotent agent to lift, but the omnipotent agent already can create such a stone; If an omnipotent agent already is more powerful than itself, then it already is just that powerful. This means that its power to create a stone that’s too heavy for it to lift is identical to its power to lift that very stone. While this doesn’t quite make complete sense, Lewis wished to stress its implicit point: that even within the attempt to prove that the concept of omnipotence is immediately incoherent, one admits that it is immediately coherent, and that the only difference is that this attempt is forced to admit this despite that the attempt is constituted by a perfectly irrational route to its own unwilling end, with a perfectly irrational set of 'things' included in that end.

In other words, the 'limit' on what omnipotence 'can' do is not a limit on its actual agency, but an epistemological boundary without which omnipotence could not be identified (paradoxically or otherwise) in the first place. In fact, this process is merely a fancier form of the classic Liar Paradox: If I say, "I am a liar", then how can it be true if I am telling the truth therewith, and, if I am telling the truth therewith, then how can I be a liar? So, to think that omnipotence is an epistemological paradox is like failing to recognize that, when taking the statement, 'I am a liar' self-referentially, the statement is reduced to an actual failure to lie. In other words, if one maintains the supposedly 'initial' position that the necessary conception of omnipotence includes the 'power' to compromise both itself and all other identity, and if one concludes from this position that omnipotence is epistemologically incoherent, then one implicitly is asserting that one's own 'initial' position is incoherent. Therefore, the question (and therefore the perceived paradox) is meaningless. Nonsense does not suddenly acquire sense and meaning with the addition of the two words, "God can" before it. Lewis additionally said that, "Unless something is self-evident, nothing can be proved." This implies for the debate on omnipotence that, as in matter, so in the human understanding of truth: it takes no true insight to destroy a perfectly integrated structure, and the effort to destroy has greater effect than an equal effort to build; so, a man is thought a fool who assumes its integrity, and thought an abomination who argues for it. It is easier to teach a fish to swim in outer space than to convince a room full of ignorant fools why it cannot be done.

Language and omnipotence

The philosopher Ludwig Wittgenstein is frequently interpreted as arguing that language is not up to the task of describing the kind of power an omnipotent being would have. In his Tractatus Logico-Philosophicus, he stays generally within the realm of logical positivism until claim 6.4—but at 6.41 and following, he argues that ethics and several other issues are "transcendental" subjects that we cannot examine with language. Wittgenstein also mentions the will, life after death, and God—arguing that, "When the answer cannot be put into words, neither can the question be put into words."

Wittgenstein's work expresses the omnipotence paradox as a problem in semantics—the study of how we give symbols meaning. (The retort "That's only semantics," is a way of saying that a statement only concerns the definitions of words, instead of anything important in the physical world.) According to the Tractatus, then, even attempting to formulate the omnipotence paradox is futile, since language cannot refer to the entities the paradox considers. The final proposition of the Tractatus gives Wittgenstein's dictum for these circumstances: "What we cannot speak of, we must pass over in silence".

Wittgenstein's approach to these problems is influential among other 20th century religious thinkers such as D. Z. Phillips. In his later years, however, Wittgenstein wrote works often interpreted as conflicting with his positions in the Tractatus, and indeed the later Wittgenstein is mainly seen as the leading critic of the early Wittgenstein.

Other versions of the paradox

In the 6th century, Pseudo-Dionysius claims that a version of the omnipotence paradox constituted the dispute between Paul the Apostle and Elymas the Magician mentioned in Acts 13:8, but it is phrased in terms of a debate as to whether or not God can "deny himself" ala 2 Tim 2:13. In the 11th century, Anselm of Canterbury argues that there are many things that God cannot do, but that nonetheless he counts as omnipotent.

Thomas Aquinas advanced a version of the omnipotence paradox by asking whether God could create a triangle with internal angles that did not add up to 180 degrees. As Aquinas put it in Summa contra Gentiles:

Since the principles of certain sciences, such as logic, geometry and arithmetic are taken only from the formal principles of things, on which the essence of the thing depends, it follows that God could not make things contrary to these principles. For example, that a genus was not predicable of the species, or that lines drawn from the centre to the circumference were not equal, or that a triangle did not have three angles equal to two right angles.

This can be done on a sphere, and not on a flat surface. The later invention of non-Euclidean geometry does not resolve this question; for one might as well ask, "If given the axioms of Riemannian geometry, can an omnipotent being create a triangle whose angles do not add up to more than 180 degrees?" In either case, the real question is whether or not an omnipotent being would have the ability to evade consequences that follow logically from a system of axioms that the being created.

A version of the paradox can also be seen in non-theological contexts. A similar problem occurs when accessing legislative or parliamentary sovereignty, which holds a specific legal institution to be omnipotent in legal power, and in particular such an institution's ability to regulate itself.

In a sense, the classic statement of the omnipotence paradox — a rock so heavy that its omnipotent creator cannot lift it — is grounded in Aristotelian science. After all, if we consider the stone's position relative to the sun the planet orbits around, one could hold that the stone is constantly lifted—strained though that interpretation would be in the present context. Modern physics indicates that the choice of phrasing about lifting stones should relate to acceleration; however, this does not in itself of course invalidate the fundamental concept of the generalized omnipotence paradox. However, one could easily modify the classic statement as follows: "An omnipotent being creates a universe that follows the laws of Aristotelian physics. Within this universe, can the omnipotent being create a stone so heavy that the being cannot lift it?"

Ethan Allen's Reason addresses the topics of original sin, theodicy and several others in classic Enlightenment fashion. In Chapter 3, section IV, he notes that "omnipotence itself" could not exempt animal life from mortality, since change and death are defining attributes of such life. He argues, "the one cannot be without the other, any more than there could be a compact number of mountains without valleys, or that I could exist and not exist at the same time, or that God should effect any other contradiction in nature." Labeled by his friends a Deist, Allen accepted the notion of a divine being, though throughout Reason he argues that even a divine being must be circumscribed by logic.

In Principles of Philosophy, Descartes tried refuting the existence of atoms with a variation of this argument, claiming God could not create things so indivisible that he could not divide them.