God, Existence, Proof, Explanation

The appearance of the proposition that God necessarily exists, among the Definitions at the outset of the Ethics, might be taken as an indication that Spinoza is circumventing its proof, because he disagrees with Descartes and others that the entity named by 'God' is absent in some respect.  However, to the contrary, he does recognize that the existence of his Deity is not immediately evident in ordinary experience, except that he diagnoses that condition non-traditionally.  On his analysis, his Deity is ever-present, but is not perceived as such because of a pervasive misunderstanding of what constitutes it.  Thus, what he offers is an explanation of what the concept of Deity entails, including, notably, that it is 'natura naturans', i. e. Nature creating itself, an ever-present, immanent process.  On that basis, a correct understanding of it can dispel any doubts that that Deity exists, is Spinoza's tack..

Revelation and Superstition

The brevity of Descartes' attention to the process of Divine Revelation leaves its classification as 'Deistic' or 'Theistic' under-determined.  For, if it consists in an elevation out of corporeality, then it might be the former, but if it involves in an ingression of his Deity into an extended being, then the latter is closer.  In sharp contrast with both, the equivalence of God and Nature in Spinoza's system entails that a Mode's knowledge of God is also a knowledge of a rationally acting Nature.  Hence, Revelation in that system consists in the dispelling of any illusion that one is separate from Nature.  From that perspective, the supernatural dimension shared by the two interpretations of Descartes' concept of Revelation, marks each as a 'superstition'.

Deity, Revelation, Extension

As Descartes' ample attention to the topic indicates, the salient characteristic of the concept of Deity to which he subscribes is that its existence needs to be proven, i. e. a characteristic of many other rival concepts is that it is to be feared, which implies that its existence is not in doubt.  Now, the need for a proof of it seems to presuppose that existence is not easily apparent, one reason of which might be that the Deity is noumenal, e. g. Platonist.  However, Descartes' concept entails the possibility of revelation, and, thus, that the Deity contingently appears. But, then, the problem is to reconcile that property with another--non-extension, a topic which Descartes' seems to leave unaddressed.

God, Deity, Extension

Insofar as Spinoza's use of 'God' is to name the object of Descartes' worship, his propositions 'God exists' and 'God possesses Extension' are expressions of agreement and disagreement, respectively, regarding that entity.  However, for Spinoza, 'God' denotes an Idea', which indicates that what it represents is, more accurately, a concept of Deity.  Thus, the fundamental target of his divergence from Descartes is the latter's concept of a Deity as fundamentally a guarantor of the reliability of Perception, which he replaces with that of a Deity as fundamentally a source of empowerment, i. e. achieved when a Mode subsumes itself under that Idea.  Similarly, Kant's alternative is that of a rewarder of Virtue, while Socrates' 'impiety' consists in his challenging the prevailing concept of Deity.  Accordingly, for both Descartes and Spinoza, the status of Extension is derivative--Perception, for the former, is unextended, while Action, for the latter, requires Corporeality, and, hence, Extension.  So what is more historically radical in the Ethics is not the attribution of Extension to the Medieval, and the Cartesian, object of worship, but the liberating establishment of the function of Philosophy with respect to any such object, which of Spinoza's successors, only Alexander seems to explicitly appreciate, i. e. in Nietzsche' 'God is dead' formulation, 'I repudiate the prevailing concept of Deity' is only implicit.

God and Extension

Because of his Parallelism, Spinoza's attribution of Extension to his God entails that it is not a product of extending from Thought.  So, though the attribution is radically heterodox, the concept itself is as static as is Descartes'.  However, that God is dynamically extensive in another respect.  For, since, according to Spinoza, every Idea is efficacious, every modification of God consists in an extending of the given.  Thus, for example, the thesis that the universe is expanding entails that so, too, is God, in his system.  Thus, while for Descartes, God is unextended while Extension is indefinite but unchanging, for Spinoza, God indefinitely extends.

Everywhere, Nowhere, Extension

'Eternity' is ambiguous--it can mean either 'at all times' or 'at no time'.  In contrast, there seems to be no single term that equivocates between 'everywhere' and 'nowhere'.  Accordingly, there is no confusing Descartes's unextended God, which is nowhere, from Spinoza's extended Deity, which is everywhere.  However, contemporary Semantic Theory is more careless.  For, according to its prevailing concept of 'extension', a term somehow is both at all its instances, and, yet, is at none of them.  So, the Everywhere-Nowhere distinction helps illuminate a confusion at the heart of theories in which that concept is operative.

Process, Reality, Extension

In Whitehead's system, 'Process' and 'Reality' are related as Producing to Product, and 'Extensive Continuum' is an arrangement of such 'products'.  Hence, he conceives 'Extension' as inert, but with no correlative generating process.  For, in the system, the structure of Process is concrescent, and, hence, contracting, until closure, whereas Extending consists in open-ended increasing.  In other words, Whitehead cannot distinguish the participle Extending from the gerund Extension.  The result is, like Bergson's, a vestige of Cartesian 'Extension' is an otherwise innovative Vitalist system, except without the ontologically pejorative connotation.

Duration, Detente, Extension

One prominent attempt to explain the origin of Extension, i. e. to not accept it as merely given, is Bergson's, which is based on his theory of the relation between Spirit and Matter.  He conceives Matter to be a spreading out of Spirit, via a process of relaxation, leading towards inertia, in which 'extension' gradually emerges in its later stages.  However, the French for that process is actually the sibling 'detente'.  Furthermore, Bergson does not consider the possible relevance of the common use of 'extend' to his concept of Duration, which can be conceived as a constant extending beyond a current moment, i. e. he does not consider that Extension can be appreciated to be a Spiritual process.  Instead, even as he bridges Cartesian Dualism, he misses the linguistic clue that the gerund 'extension' is the product of the participle 'extension'.

Extension, Intention, Intension

Brentano's doctrine 'Intentionality', primarily via Husserl, has had a strong influence on Contemporary Philosophy.  Now, while his use of the term is consistent with that of common parlance, i. e. with 'intend', the structure of the connoted process is actually one of extending, i. e. one of a projection from a thought to an external object.  Furthermore, this 'intentionality' and 'intend' are antithetical to the term 'intensional', which, in Semantic Theory, pertains to a purely internal characteristic, as does the common use of 'intense'.  However, at the root of this inconsistencies is not some Philosophical Babel, but the etymological anomaly that 'tend' is virtually synonymous with 'extend', i. e. both are equivalent to 'stretch out'.  Still, the Philosophical program, i. e. Analytic Philosophy, the mission statement of which is to clear up mental confusion caused by imprecise language, has only perpetuated the disorganized use of this family of terms.  In this respect, it carries on a tradition that Descartes initiates, with his careless, as has been previously discussed, use of 'extension'.

Extension and Meaning

Pointing to an object usually involves extending a finger, hand, and/or an arm in the direction of it.  Thus, the 'extension' of a term could, with linguistic justification, be its referent.  However, such an act is a specific event, so the generalization of 'extension', common in Contemporary Semantic Theory, to every exemplification of a term, abstracts from a distinctive facet of Referring, and, hence, from that justification.  Accordingly, even less grounded is the use of 'extension' by Nominalists, for whom the Word-Object relation is, quite to the contrary, a contraction from the latter to the former.  Now, Russell's misuse is more complicated, the apparent product of an effort to reconcile Nominalism with Logicism, e. g. his concept of Number abstracts from its exemplifications, and, yet, entails relations that he posits as independent of empirical experience.  So, for him, a non-oriented, inert version of 'extension' mediates that reconciliation--it correlates Word/Number and Object, with neither pole as prior.  Thus, like Descartes' version, it reflects a systematic exigency, rather than nay Philosophical insight into the process of Extending.

God, Extension, Divisibility

Descartes writes in the Third Meditation, "The unity, simplicity, or the inseparability of all things which are in God is one of the principle perfections which I conceive to be in him", and in Principle XXIII, "Since divisibility is included in local extension, and divisibility indicates imperfection, it is certain that God is not body."  So, plainly, his concept of 'extension' is significant insofar as it connotes 'divisibility', as part of a Theological doctrine that entails the superiority of Unity over Multiplicity.  However, he seems unaware of two distinctions between the gerund 'extension' and the participle 'extension': 1. The former presupposes the latter; and 2. The former, as inert and unoriented, is divisible in a way that the latter, as an ordered continuous process, is not.  Clearly his concept is the derivative gerund version, reflecting Theological exigency, rather than Philosophical insight into the process of Extending that first produces what the term connotes to him.  In contrast, possible implications of such an insight are manifest in Spinoza's system, in which dynamic Extension is not antithetical to God, but, to the contrary, a divine attribute.

Extension, Meaning, Ordinality

Like Descartes, Russell problematically relies on an hypostasization of the process connoted by 'extend'.  In his case, the abstraction is effected in his Semantic Theory, according to which the 'extension' of a concept is all its exemplifications.  Thus, for example, the 'extension' of '3' is the set of all triples.  Common to the two uses of the term is an ambition to retain the priority of the Unextended over the Extended, e. g. Mind over Body, Number over Manifold, while preserving their simultaneity, without which their segregation is difficult to maintain.  Also common to the two is a contrast with a better-grounded use elsewhere in the system--Descartes' implicitly ordinal Geometric Space, and Russell's ordinal generation, via his Successor Function, of Numbers, each of which of which is more literally 'extensive'. 

Extension and Ordinality

To 'extend' means to 'increase from a given', and, hence, connotes an ordinal process.  Thus, while the common use of 'extension' is etymologically proper, the seminal Philosophical one is not.  For, while 'building extension' and 'extension of a period to pay' signify adding to a whence, Descartes' 'Extension', the essence of Corporeality in his system, does not.  In contrast, his concept of Geometrical Space is ordinal, as is expressed by the centrifugal enumeration of its points with respect to a center, and, thus, does possess 'extension'.  So, in the absence of an application of that model to Corporeality, e. g. with Mind as the center of Body, or with the Universe as emanating from God, his prominent use of the term 'Extension' in the Meditations and the Principles is profoundly erroneous.

Geometry, Ordinality, Cardinality

Perhaps the most significant feature of Cartesian Geometry is the introduction of an Origin into Space.  Thus, for example, the priority of Ordinal Numbers over Cardinal Numbers is thereby illustrated.  For, with that innovation, Space is rendered oriented with respect to it, i. e. along a line emerging from the Origin, distinguishable are the point nearest to it, from the point next nearest, from the next point, etc.  Or, numerically expressed, they can be characterized as the first point, the second point, the third point, etc, i. e. expressed as Ordinal Numbers, on the basis of which the Cardinals, i. e. 1, 2, 3, etc., can be derived.  But, the converse is not possible.  For, as is clear in Platonism, The One, The Two, The Three, etc. are mutually discrete, and, hence, are as non-ordered with respect to one another as are the Triangle and the Square.  In other words, Cartesian Geometry illustrates how the sequence of Numbers, qua sequence, is essentially Ordinal, even as they are commonly abbreviated as Cardinal.

Theology, Cardinality, Ordinality

The historical Socrates fatally directed his skepticism at the prevailing Theology of the era, which Plato replaces with a Pythagorean Cosmology, i. e. his World of Forms is based on the Mathematical model of the latter.  In contrast, Descartes attempts to use his Skepticism to reinforce the Theological dogma of the time, a project which includes a subordination of the Pythagorean Cosmology, expressed as Mathematical propositions, to the power of his God.  However, he is apparently unaware of the distinction between Cardinal and Ordinal Numbers, so, in the process relegating the former, he takes the later for granted, i. e. his Method, as has been previously discussed, presupposes the distinctions between First, Second, etc., as much as does the God of the outset of Genesis.  So, it may not be extrinsic to his Philosophical writings, wittingly or otherwise, that his greatest impact on subsequent society has been the 'Cartesian Plane', i. e. the forerunner of every graph, which is based on the enumerability, i. e. the Ordinality, of location.

Whenever I Think, Then I Am

According to Propositional Logic, 'A, therefore B' is equivalent to 'If A, then B', and to 'Whenever A, then B'.  Furthermore, according to Modal Logic, 'necessarily (If A, then B)' is not equivalent to 'If A, then necessarily B'.  Now, if it is granted that Descartes demonstrates: 1. Whenever I doubt, I am thinking; 2. Whenever I think, I exist; 3. Whenever I think, God exists; and 4. Whenever I exist, God exists, it still does not follow that 5. It is certain that I think; 6. It is certain that I exist; or 7. It is certain that God exists.  So, despite his expression of respect for the Law of Contradiction in Principle VII, his presumption that he has demonstrated #5, #6, or #7 on the basis of 'I can doubt my sense experience', is based on loose Logic.

Doubt and Contradiction

Descartes' assertion, in Principle VII, that 'I am' is the "first and most certain" of all propositions seems to overlook the prior establishment of 'I think', via the implicit argument, 1. I cannot doubt that I am doubting; 2. Therefore, 'I doubt' is certain; and 3. Doubting is a species of Thinking.  Regardless, textually notable in the passage is the invocation of the Law of Contradiction, which does not explicitly appear at comparable stages of either the Discourse or the Meditations.  However, the reference is also a reminder that he has failed to vet the Law--e. g. on the grounds that God may be deceiving him--which he could explore with at least as much justification as submitting Mathematics to the test.  So, one diagnosis of this neglect is that his concept of Will, in either its human or its divine mode, is not absolutely 'free', i. e. because it is constrained by Logic.  Another is that recognizes that without the Law, he would be trapped in a Skepticism, with the establishment of 'I think', 'I am', and 'God exists', thus, a lot more difficult, at best.

Doubting Doubt

At every stage of the application of his method, Descartes' reasoning is 'I can imagine that the situation is other than it appears to be.  Therefore, I can doubt it.'.  Likewise, if an appearance is possibly false, it is because some alternative is possibly true.  Similarly, volitional liberation from the given is entailed in the creative replacement of it.  Thus, while his concept of 'Doubt' may be 'clear', it is not 'distinct', i. e. its object in each of his examples is not atomic, but only a facet of a more comprehensive process.  In other words, according to his own criterion, his concept of 'Doubt' is dubious.

Free Will and Doubt

As has been previously discussed, Descartes introduces, in the Fourth Meditation, Free Will in order to explain how humans, not God, are responsible for Evil, i. e. via the affirmation of ideas that are not perceived clearly and distinctly.  In contrast, in the Principles of Philosophy, he derives it prior to the establishment of the existence of God, in #VI, as that which "causes us to abstain from giving assent to dubious things".  In other words, in that passage, he conceives the function of Free Will as fundamentally negative, with respect to which a further derivation of a positive function, e. g. affirmation, assent, is thus required.  However, such a proof is lacking, both in the Fourth Meditation, and, later, in the Principles.  Nor does the attribution of the affirmation of 'I think' suffice in that regard--for that idea is clearly and distinctly perceived, whereas what is needed is an account of how ideas not so perceived can be freely assented to, i. e. how humans can be responsible for Evil.  Thus, Principle VI reinforces the suspicion that Descartes' eventual concept of Free Will is no more than an ad hoc device in the service of Theological dogma.

Free Will, Evil, Culpability

As has been previously discussed, the concept of human Free Will often seems less a product of Psychological observation than a device to exonerate a good and omnipotent God from the existence of Evil.  For example, Descartes advocates a version of the Theological thesis, by asserting that error and sin are derived from an abuse of Free Will i e. from choosing what is not clearly and distinctly perceived.  Now, on the one hand, in the Fourth Meditation, he presents Free Will as as absolute as divine Free Will, but, on the other, in the same paragraph, he discerns a difference of degree between them, in terms of "knowledge" and "power".  So, regardless of what he means by those latter two, the qualification implies that Free Will, in general, is a variable quantity, dependent on other factors.  If so, then it is not as absolute a factor in human experience as Descartes posits it to be, in which case culpability for Evil is not as easily assignable to humans as he presents it to be.  Thus, while that nuanced variability, that he himself allows for, might better explain concrete motivation, e. g. impulsive behavior, it undermines his Theological presuppositions more than he seems to recognize.  In contrast, Aristotle and Spinoza each offers an example of a concept of Volition not constrained by those presuppositions.

Will, Thinking, Theology

While 'Free Will vs. Determinism' is typically categorized as a 'Metaphysical' debate in contemporary Philosophy, it is actually a vestige of a Theological problem.  For, what is originally, for Aristotle, a situational Psychological nuance--Voluntary vs. Involuntary--becomes exaggerated as the solution to the following Theological conundrum: 1. God is omnipotent; 2. God is good; 3. Evil exists.  That is, divinely bestowed human 'Free Will' accounts for #3 without compromising either #1 or #2.  Now, as Descartes explains, in the Fourth Meditation, God, too, possesses Free Will.  But, God is incorporeal.  Therefore, in this scheme, the source of Free Will can only be Mind, which clarifies why Descartes classifies Will as a species of 'Thinking', even as he opposes it to another species, 'Understanding'.  So, in two respects, his concept of Will is determined by Theological systematic exigency, rather than by perceivable characteristics of actual human motivation, as it is for Aristotle.  Also in contrast, Spinoza denies #3, leaving no need to posit the existence of a 'Free Will' that is separate from what Descartes calls 'Understanding'.

Thinking, Preface, Intention

In the Preface to the Meditations, Descartes explains that what follows is an elaboration of two topics more briefly considered in the Discourse--the existence of God, and the separation of Mind, or Soul, and Body.  Thus, wittingly or otherwise, the text as a whole illustrates a common function of Thinking--the formulation of an Intention, and the execution of it, i. e. its guidance of subsequent processes.  Now, the allusion in the Preface is to part IV of the Discourse, which is preceded by, in part III, a proclamation of unquestioning allegiance to his religion, from which it can be inferred that he accepts the dogma of the theses that God exists and that Soul and Body are separate.  So, perhaps, the two significant previously discussed flaws in the Meditations--1. The abstraction, from the outset, of a contemplative exercise from an act of writing, and 2. The inference from the possibility one's bodily experience is other than it seems to be, to the possibility that one has no body-- inadvertently show how evidence can be tainted by a prior commitment.  Regardless, the common contemporary academic practice of abstracting the Meditations from that Preface only facilitates the misrepresentation of the work as a presupposition-less exercise in Method.

Thinking, Method, Ordinality

Arriving at Cogito, Descartes goes no further to clarify the concept of Thinking, other than to list, questionably, as has been argued, some of its species, e. g. Willing.  However, if his own efforts are any evidence, Thinking can be conceived as an esentially Methodical process, and, hence, as one entailing Ordinality.  Accordingly, he can be interpreted as a forerunner of both Spinoza and Kant, for whom Thinking consists in ordered Extending, and Objective ordering, respectively.  In his own case, this concept of Thinking is more appropriate to his self-evidently actual process of Writing, than to his described sedentary meditating.

Method, Ordinality, Doubt, Mathematics

In #V of the Rules, Descartes asserts that "order" is the essence of Method.  Now, Order is typically expressed by Ordinal numbers, often represented as a sequence of Cardinal numbers.  Thus, his Method of Doubt is governed by Ordinality, not only as evinced by the passage in part II of the Discourse, in which he summarizes "The first . . . the second . . . the third . . . the last", but by his mere enumeration of chapters in both that work and the Meditations.  Furthermore, the Ordinal principle by which any nth term transitions to the (n + 1)th is the basis of Addition, and, hence, of all Arithmetical operations.  Thus, even as Descartes is subjecting Mathematics to his Method, he is presupposing the truth of its propositions.  Indeed, both his evil God and his good God, are likewise governed by Ordinality.

Clear and Distinct

Some scholars attribute to Descartes the thesis that being 'clear and distinct' is a characteristic of a 'true' idea, one which they analyze as being defended by 'circular' reasoning.  Now, that thesis is implicitly expressed in the Rules, and hence, without defense.  However, in part IV of the Discourse, he asserts that "things which we conceive clearly and distinctly are all true--remembering, however, that there is some difficulty in ascertaining which are those that we distinctly conceive".  Furthermore, in the Third Meditation, he explains that an idea that is perceived clearly and distinctly is a true idea only if it is not the product of a deceiving God.  So, at minimum, these passages suggest that his concept of 'clear and distinct' is dubious as an indication of Truth, and the difficulty is to glean from them whether or not it is wittingly so.  At face value, they do express a reconsideration of that status of the concept, in which case there is no circularity involved.

Deception and Incorporeality

The possibility that Descartes is an incorporeal being enters the Meditations in two ways--as an inference from the example of dreaming, and as a consequence of the hypothesis that God is evil.  But, the inference from dreaming is invalid.  For, the deception in dreaming consists in a discrepancy between two corporeal scenarios, e. g. between one running, and one sleeping in a bed with legs twitching.  Thus, the extrapolation to a discrepancy between a corporeal scenario and an incorporeal one is ungrounded, e. g. a brain in a vat is as much a corporeal entity as the full body that it is stimulated to imagine.  Furthermore, once the hypothesis that God is evil is refuted, in the Third Meditation, so, too, is part of the consequence of that hypothesis, namely, the thesis that Descartes is actually an incorporeal entity.  So, Mind-Body Dualism does not follow in the Meditations from a rigorous exercise of his Method, but it could reflect a prejudice central to his Theological affiliation, i. e. the separation of Soul and Body.

I Think, Therefore God Exists

Descartes' famous phrase, 'I think, therefore I am', appears in the Discourse on Method, but not in the Meditations, not adventitiously, but because it is a stage in the former, but not in the latter.  In the Discourse, 'I think', via the irreducibility of the application of the method of Doubting, is the first certainty at which he arrives., from which 'I am' follows.  In contrast, in the Meditations, the axiom is 'I exist', derived from 'An evil God may be deceiving me', via the irreducibility of the deceived 'me'.  From there in the Meditaitons, he next proves that 'I am a thinking being', which supplies him with the proposition 'I have a thought of God', which serves as the premise of both the Third and Fifth Meditations, in proofs of the existence of God.  Furthermore, the topic of the Fourth Meditation--"Of the True and the False", extends the one of the Theological concepts--Perfection--of the Third, i. e. in establishing that because God is perfect, and deception involves imperfection, God is not a deceiver..  So, while the staple in academic curricula is the more explicitly Theological of Descartes' two mature works, his greater influence, not only on the popular image of him, but in the primacy of Epistemological methodology--Empiricism, Rationalism, Phenomenalism, Transcendentalism, Phenomenology, etc.--in subsequent Modern Philosophy, stems from the other book.  In other words, the Discourse presents his Philosophical innovation, while the Meditations merely continues the Medieval tradition of subordinating Philosophical methods to Theological purposes, i. e. its primary theme can be expressed as 'I think, therefore God exists'.

Will, Thinking, Proof

Insofar as Will is a species of Thinking, as it is in the Meditations, it is bound by the laws of the Intellect.  So, for example, on the basis of that classification, it is logically impossible to doubt the existence of God once that is proven in the Third Meditation.  In contrast, insofar as Will is independent of Thinking, as it is in the Rules for the Direction of the Mind, its operations, e. g. Doubting, Disbelief, Denial, etc. are not bound by the Law of Contradiction.  So, for example, on that basis the result of the Third Meditation does not entail the indubitability of the existence of God.  Thus, though Descartes never explains the subsumption of Will under Thinking in the later work, it does eliminate from its development a profound complication.

Doubt and Freedom of Choice

As has been previously discussed, in the earlier Rules, Belief and Disbelief are modes of Will, which is independent of Thinking.  So, prior to the subsumption of the former under the latter, the Cognitive problem of Doubt vs. Certainty is a Volitional one of Freedom of Choice vs. Necessity.  Accordingly, the quest for Certainty is a quest for Necessity, with the result that Freedom of Choice is Necessary, anticipating Existentialism, especially Sartre, by several centuries.  Likewise, in hindsight, Descartes' subsequent reliance on the archaic, eventually repudiated, Proofs of the Existence of God, seems a crutch for his consequent innovations in Mathematics, though, more charitably, in the historical context, his Theology can be interpreted as functioning as parental assistance in a baby learning to walk.

Belief, Doubt, Will, Thinking

At first glance, the Rules for the Direction of the Mind and the Meditations are complementary--the former expounds the Axiomatic Method, i. e. the derivation of compound propositions from a simple one, while the Method of Doubt in the latter supplies the Axiom.  So, the introduction in the later work of the Cogito as that ground of all Knowledge constitutes no conflict with the Rules, in which it does not appear.  However, the status of Doubt seems to shift significantly between the two projects.  For, while in the later, it is plainly a cogitation, at the end of Rule III,  Belief or non-Belief is "an action not of our intelligence, but of our will."  Now, in the Second Meditation, a thinking being is one which "doubts . . . affirms, denies, wills . . . ".  So, apparently a fundamental difference between the two works is the classification of Will, i. e. as a species of Thinking, or not.  Still, the later subsumption, i. e. of Will under Thinking, does not, in itself, repudiate the earlier insight that withholding Belief, and, hence, Doubting, is Volitional.  It just indicates that the more immediate result of the Second Meditation is 'I will, therefore I am, via 'I cannot disbelieve that I am disbelieving', and prior to its generalization into 'I think, therefore I am'.