IDEAS. So central were ideas to philosophy in the 17th century that the Port-Royal Logic could declare at the head of its first chapter: “Some words are so clear that they cannot be explained by other words, for none are more clear or more simple. ‘Idea’ is such a word. All that can be done to avoid mistakes in using such a word is to indicate the incorrect interpretations of which it is susceptible.” Traditionally, the term in its modem sense is attributed to Descartes. Descartes himself gives this impression when he tells Thomas Hobbes “I used the word ‘idea’ because it was the standard philosophical term used to refer to the forms of perception belonging to the divine mind, even though we recognize that God does not possess any corporeal imagination. And besides, there was not any more appropriate term at my disposal” (AT, vol. VII, p. 181). Descartes borrowed a term used to refer to God’s ideas (the post-Augustinian heir of the Platonic or neo-Platonic “Idea”), and, as he remarked elsewhere, used it more generally for “everything which is in our mind when we conceive something, no matter how we conceive it” (AT, vol. III, p. 393).
Ideas, for Descartes, are “as it were images of things,” mental acts that represent something. By calling on the ideas in God’s mind as his source Descartes set ideas free from their link to sensation. In taking this path Descartes seems to have canceled out the major context of the traditional doctrine of ideas: the context of archetype or model, where the idea informs its imitations, and gives them, or their “images,” such reality as they have. Traditionally, ideas are identified with forms or species: they have power through a certain agency; they are “efficacious,” unlike particular things, which are relatively inert. It is ideas that, primarily through God’s thought, make things what they are. Analogously, though of course in a lesser degree, an artist’s mind can produce a copy of a reality, itself in turn informed by the divine patterns, the ideas, in God’s mind. Cartesian ideas, patterned after God’s pure cogitations, are entertained by minds. They are psychological units such as the ones mathematicians use in thinking through problems, thinking of thousand-sided figures as easily as of triangles and pentagons, which they could, but need not, imagine. Ideas as concepts, whether formal or objective, are the units by which Descartes can free pure mind from its scholastic bonds to sense. Descartes made a new start in philosophy with his “idea,” but he shaped this new conception by using readily available meanings of the term and purifying them of much of their habitual connotations.
IDEAS, INNATE. In the Third Meditation, Descartes examined his ideas and divided them into three kinds: innate, adventitious (that is, coming from the outside), and factitious (or produced by him). He then considered his idea of God. He decided that it did not derive externally from the senses and he did not produce it. Thus, his only option was that this idea was innate in him, just as his idea of self (cogito) was. Descartes defended this line of reasoning, in his Replies to Objections, against the objections of Thomas Hobbes, Pierre Gassendi, and others. The criticism that elicited the most interesting response, however, occurred when Descartes responded to his erstwhile supporter Henricus Regius, in Notes Against a Program (Notae in Programma).
Regius’s broadsheet included the following three anti-Cartesian propositions: “The mind has no need of innate ideas, or notions, or axioms, but of itself the faculty of thinking suffices for performing its own acts. Therefore all common notions, engraved on the mind, owe their origin to the observation of things or to tradition. In fact the very idea of God implanted in the mind is the outcome of divine revelation, or tradition, or the observation of things” (AT, vol. VIII-2, p. 345). Descartes called Regius’s dissent in the first proposition merely verbal, because, as he said, he had not asserted that “the mind required innate ideas that were in some way different from its faculty of thinking.” Descartes defined ideas as innate “in the same sense we say that in some families generosity is innate, in others certain diseases like gout or stones,” that is, the families “are born with a certain disposition or propensity for contracting them” (AT, vol. VIII-2, p. 358). He denied Regius’s second statement, arguing that “no ideas of things, in the form in which we envisage them by thought are presented to us by the senses.” Descartes’s possibly radical account was that “nothing reaches our mind from external objects through the sense organs beyond certain corporeal motions. . . . But even these motions and the shapes arising from them are not conceived of by us exactly as they occur in the sense organs. . . . Hence it follows that the ideas of the motions and shapes are themselves innate in us. So much the more must the ideas of pain, color, sound and the like be innate, so that our mind may, on the occasion of certain corporeal motions, represent these ideas to itself, for they have no likeness to the corporeal motions” (AT, vol. VIII-2, p. 359). Descartes replied to the third proposition by distinguishing between proximate, primary causes and remote, accidental causes: “Tradition or observation is a remote cause, inviting us to give attention to the idea we can have of God, and to present it vividly to our thought. But no one can maintain that this is the proximate and efficient cause, other than the person who thinks that we can understand nothing about God, except that he is called God” (AT, vol. VIII-2, p. 360).
IMAGES. See IDEAS.
IMAGINATION. Toward the start of the Sixth Meditation, Descartes held that the distinction between imagination and pure intellect is revealed by the fact that he cannot distinctly imagine a chiliagon, or thousand-sided figure, though he can demonstrate that this figure has certain properties (AT, vol. VII, p. 72). He then hypothesized that this distinction is due to the fact that imagination involves an “inspection” of a bodily image, whereas pure intellect involves the mind’s inspection of one of its own ideas. Though he dismissed this explanation as merely probable, Descartes did suggest that imagination depends on the body in a manner that distinguishes it from pure intellect. The suggestion is that both this faculty and the faculty of sensation require the soul-body union. That suggestion is confirmed in Descartes’s physiological works. In the Treatise on Man, for example, the “man-machine” is credited with a purely corporeal faculty of recomposing images impressed upon the ventricles of the brain. Animals too may have an imagination of this sort. Descartes thereby manages to maintain agreement with Aristotelian theories according to which imagination belongs to the “sensitive” part of the soul, a part we share with animals, while eliminating much of the complexity of Aristotelian discussions of the internal senses. The distinction between imagination and intellect, on the other hand, though in keeping with standard claims that the intellect has no bodily organ, departs from accounts according to which the so-called “active” intellect, in certain of its operations, draws upon “species” stored in the brain.
Descartes generally indicated a preference for clear and distinct intellectual ideas over confused images in the search for truth. Indeed, in the Second Meditation he emphasized that the knowledge of the piece of wax as something extended, flexible, and mutable goes beyond what can be understood through the imagination (AT, vol. VII, p. 30). The limitations of imagination, because it has a corporeal instrument, derive from those of body; in the Treatise on Man, Descartes compares the storage of images in the brain to the punching of holes in cheesecloth: only so many images can be stored before they begin to impinge upon one another—hence their “confusion.” Nonetheless, Descartes wrote to Princess Elisabeth of Bohemia that though bodily qualities such as extension, shape, and motion can be known “by the intellect alone,” they are known better by “the intellect aided by the imagination” (AT, vol. III, p. 691). There is an anticipation of this view in Descartes’s first work, the Rules for the Direction of the Mind, which includes the proposal that problems concerning extension should be “pictured in the imagination entirely by means of bare figures” (AT, vol. XI, p. 438). Thus, even though knowledge of body cannot derive from the faculty of imagination alone, the suggestion in these texts is that we arrive at such knowledge most readily through use of this faculty.
IMMORTALITY. The first edition of the Meditations bears the subtitle “in which is demonstrated the existence of God and the immortality of the soul.” In the dedicatory letter to the Sorbonne, moreover, Descartes emphasized the call of the Lateran Council (in 1513) for Christian philosophers to seek to prove by natural reason that the soul does not die with the body (AT, vol. VII, p. 3). However, he warned in the synopsis of the Meditations that he did not produce a proof of the immortality of the soul since this depends “on an account of the whole of physics” (AT, vol. VII, p. 14), and in particular on his view of both the indestructibility of bodily substance “considered in general” and the difference between individual human bodies and souls. In response to a point raised in the Second Set of Objections, moreover, Descartes conceded that he cannot prove by natural reason alone that God does not limit the duration of the soul since this depends on his free will and absolute power (AT, vol. VII, p. 108f). These qualifications help to explain why the second edition of the Meditations promises in its subtitle only a demonstration “of the distinction between the human soul and the body.” Yet Descartes consistently maintained that his dualism supports the belief in immortality insofar as it shows that the soul is a substance that is really distinct from and thus can exist apart without the body.
INDEFINITE. Descartes distinguished between the infinite and indefinite in a manner similar to Aristotle’s distinction between actual and potential infinities. In Aristotelian parlance, an actual infinity is a completed whole, while a potential infinity is unending and never complete. So, in Aristotle’s view, a line segment is potentially divisible to infinity, in the sense that the process can always be continued, but it cannot be actually divided to infinity, since the completion of such a division process would compose the continuum out of dimensionless points. In the Principles, Descartes announces, “in all those things in which, according to some way of considering them, we discover no limits, we will not affirm that they are infinite, but will regard them as indefinite” (AT, vol. VIIIA, p. 15). Only God is truly infinite in this sense, as Descartes explained in a 1649 letter to Henry More: “It is only God that I positively understand to be infinite, while in the case of other things, such as the extension of the world or the number of parts into which matter is divisible, I confess I do not know whether they are absolutely infinite; I only know that I know no end to them, and so looking at them from my own point of view, I say they are indefinite” (AT, vol. V, p. 274).
INDIFFERENCE. See FREEDOM/INDIFFERENCE.
INDUCTION. See ENUMERATION.
INERTIA. Stated generally, inertia is the tendency of a body to remain in whatever state it is in at a given time, or the inability of a material body to change its state spontaneously. More specifically, the famous first law of motion in Isaac Newton’s Principia asserts that a body in uniform rectilinear motion will remain in motion, and a body at rest will remain at rest unless acted upon by an external force. Newton was not the first to formulate an inertial principle. Descartes formulates his first law of nature in the Principles of Philosophy as the claim that “each and every thing, in so far as it can, always continues in the same state; and thus what is once in motion always continues to move” (AT, vol. VIIIA, p. 62). This is an immediate consequence of the conservation principle that “God is the primary cause of motion, and always conserves the same quantity of motion in the universe” (AT, vol. VIIIA, p. 61). Descartes reasons that only God can be understood as the “first and general” cause of motion in the world, so the conservation of “quantity of motion” follows from the nature of God. Further, God’s constancy requires not only that the universe contain the same quantity of motion from instant to instant, but also that a body, whether in motion or at rest, will not spontaneously change its state. The inertial principle therefore appears as a consequence of divine immutability. Other thinkers, notably Galileo Galilei and Thomas Hobbes, proposed similar inertial principles, and all were united in rejecting the Aristotelian doctrine that terrestrial bodies in motion tend naturally toward rest.
INFINITE. A traditional epistemological and methodological tenet is that the finite human mind is incapable of reasoning about anything infinite. Notorious paradoxes of infinite divisibility or the problem of composition of the continuum underwrite the principle that our reasoning should be confined to the case of finite things. Especially in mathematics, the notion of infinite magnitudes has long been taken to be the source of error, confusion, and downright contradiction. It is therefore somewhat surprising that Descartes should make the idea of the infinite a centerpiece of his epistemology, as he does in the Third Meditation. Descartes’s proof of the existence of God and his accompanying move from the awareness of the thinking self (gained by the cogito) to secure knowledge of the external world proceed by way of the idea of an infinitely perfect God. Notwithstanding the linguistic fact that the term infinite is expressed as the negation of the finite, Descartes takes the idea of the infinite as a simple positive idea that is maximally clear and distinct: “I should not think that I perceive the idea of the infinite, not by means of a true idea, but only by negation of the finite” (AT, vol. VII, p. 45). In Descartes’s view, the idea of the infinite is conceptually prior to the finite, and we actually understand the finite in terms of the negation of the infinite. More importantly, the idea of the infinite cannot have been constructed from experience—we grasp the concept of an infinitely perfect God and see that it cannot be generated by continually increasing the idea of some perfection. Such an idea would at best be of something indefinite, rather than infinite: “I judge God to be actually infinite, so that nothing can be added to his perfection” (AT, vol. VII, p. 47).
There remains the difficulty of explaining how a finite mind can have a clear concept of the infinite, and how to avoid the traditional paradoxes of the infinite. Descartes held that the human mind could not have complete or adequate knowledge of the infinite, but that finite humans can come to understand that it exists and clearly grasp at least some of its properties. Speaking of the idea of God, Descartes argues: “Nor is it an objection that I do not comprehend the infinite. . . . For the nature of the infinite is such that it is not comprehended by a being such as I, who am finite. It is sufficient that I understand this very point and judge that all those things that I clearly perceive and that I know to contain some perfection—and perhaps even countless other things of which I am ignorant—are either formally or eminently contained in God” (AT, vol. VII, p. 46). The paradoxes of the infinite arise, not in the case of God, but in the attempt to reason about the indefinite as if it were a completed whole. Yet if we keep the distinction between indefinite and infinite in mind, such paradoxes will be avoided.
INTELLECT. Sometimes Descartes spoke of the intellect as the mental faculty of perception in general that is distinct from the faculty of will, and sometimes he spoke of it as a particular faculty of perception distinct from the perceptual faculties of sensation and imagination. In the first sense, the intellect is what contributes the ideas that, when combined with volitional acts of assent or dissent, yield judgments that are capable of truth or falsity. The second sense of intellect—sometimes called “pure intellect”—is required to distinguish perceptions that the mind possesses apart from the body from perceptions that the mind can possess only in virtue of its union with a body. Descartes indicated that it is the faculty of pure intellect that best reveals the real distinction between mind and body, since it is this faculty that shows most clearly that mind can exist without the body. Nicolas Malebranche later endorsed the claim in Descartes that we have a pure intellect that can operate independently of the body, whereas Robert Desgabets and Pierre-Sylvain Régis rejected the existence in us of pure intellect on the grounds that the temporality that infuses all of our thoughts can exist only if such thoughts are united with bodily motion. See also DUALISM.
INTUITION (INTUITUS, CONNAISSANCE INTUITIVE). According to the Rules for the Direction of the Mind intuition is, next to deduction, one of the two fundamental ways of knowing things. Accordingly, the aim of the method is to teach how to use intuition and how to find deductions. Other things are not required and would in fact make it more difficult for us to know something. Descartes defines intuition as “the concept of a pure and attentive mind which is so easy and so distinct that there can be left no doubt about the thing we understand, or, what is actually the same thing, the concept, free from doubt, of a pure and attentive mind, which is born only from the light of reason and is more certain than deduction because it is more simple” (Rules III, AT, vol. X, p. 368). Although in at least one passage Descartes seems to identify intuition with experience, and although in later parts of the Rules Descartes also envisages intuitions of sense perceptions and images, he explicitly denies that intuition can be our trust in the senses (which is fluctuating) or a judgment of the imagination (which is deceptive).
Descartes is conscious of the novelty of this definition; indeed scholastic philosophers had reserved intuition for sense perceptions. So intuition seems to be characterized by the fact that it is proper to the intellect (even if the object is given in the imagination), that it takes away all doubt, that it is simple and that it is easy, but that to have an intuition we should have a “pure and attentive mind.” Thus, according to Descartes, everybody can have the intuition that he exists, that he thinks, that a triangle is terminated only by three lines, and so forth. But it can also have a more complex object. Thus, for example, to know that 2 + 2 is the same as 3 + 1 all we need is an intuition of 2 + 2 = 4 and of 3 + 1 = 4. So if we do have clear intuitions of those, we necessarily see what follows from it, namely that 2 + 2 = 3 + 1. The only specific difference between intuition and deduction is that deduction relies on memory, whereas intuition is a matter of direct apprehension. Accordingly there are many problems that some people can solve by intuition, whereas others would use deduction. This much is clear: first principles are always the object of an intuition, whereas remote conclusions are always the object of a deduction. In any case, the essence of method is that we should try and reduce a problem to things of which we can have an intuition and then try and see what can be deduced from it, that is, determine the relation between what is known (by intuition) and what is, as yet, not known.
There are no specific rules for intuition, except that whatever is intuited is more or less simple and that, as we concentrate, we become perspicacious (just as for deduction we must be sagacious). This can be trained: “Artisans who are exercised in minute works and have accustomed themselves direct their eyes to single points, acquire by training the capacity to perfectly distinguish even the smallest and subtlest objects; and in the same way those who avoid to distract their thought by many different objects but always occupy themselves with the simplest things that are also the most easy to consider, become perspicacious” (Rules IX, AT, vol. X, pp. 400–01).
In Descartes’s later work the term intuition (intuition of the mind) seems to be replaced by that of natural light, sometimes in the same opposition to demonstration as intuition to deduction. Thus, for example, it is clear by the natural light that if I doubt I must exist, that a cause must have at least as much reality as its effect. It teaches me that, to the extent that a false thought represents something that does not exist, it must come from nothing, that is, that it is in me only insofar as something is lacking to my nature; that there is no difference between creation and conservation; that deceptiveness depends on a defect; that the determination of the will is preceded by knowledge of the intellect; that whatever exists by its own force exists always; that no more than one sovereign being can be independent of everything else; that a thing that knows there is something more perfect than itself cannot be the cause of itself; and numerous other things. Natural light requires a lot of attention, which can be distracted by the perception of the senses, by which it can be obscured and blinded. Inversely, to the extent that natural light “sees” anything at all it must be true.
Even so, Descartes continues to speak, in accordance with tradition, of a certain type of knowledge as being intuitive, that is, not based on inference. Thus, for example, in a letter to an unknown correspondent Descartes claims that by meditating on the first things I certainly know, namely, that I think, that I am, that I am a soul, that is, a being that can exist independently from the body and whose essence it is to think, I acquire a “very certain and, if I may say so, intuitive knowledge of intellectual nature in general” (AT, vol. I, p. 353). Similarly, in a letter to Jean de Silhon of March 1648 he claims that the difference between the knowledge of God we have now and the one we will have in beatitude is that the second will be “intuitive.” Intuitive knowledge is “an illumination of the mind by which it sees in the light of God whatever it pleases God to reveal to it by a direct impression of the Divine clarity on our intellect, which in such a case is not seen as an agent but as something receiving the rays of Divinity,” whereas in this life all natural knowledge we may have of God proceeds by reasoning (AT, vol. V, pp. 136–37).