Version 2.01, October 31, 2005
Modern philosophy begins with the rejection of the authority of Aristotle, and (more discreetly) of the authority of the Bible and the pronouncements of church leaders. Martin Luther's appeal to individual conscience as the standard for religious belief encouraged independent thinking. The other chief stimulus was the recovery of a vast number of ancient texts, which suggested new ways of studying nature.
Aristotle's authority was not alone in coming under fire by the early modern philosophers. The medieval method of investigating the world, which has its origins in Aristotle, was increasingly rejected as well. For Aristotle, scientific knowledge begins with sense-perception, which reveals the universal under which a given kind of thing stands. All knowledge is supposed to be deduced from what are in effect definitions.
As opposed to this method, the modern philosophers advocated observation and experiment. Moreover, they invented mathematical modeling techniques to systematize what they observed and to gain information about what is unobserved. The main innovations in the normative project are found in these investigative techniques.
It is convenient to distinguish two kinds of epistemic norms: those that govern basic knowledge or assent and those that govern derivative knowledge or assent. Most commonly discussed in the first group are rational intuition, perception (both sensory and introspective), and common sense. Among the important items of discussion in the second group are deduction, probability, testimony, inference to the best explanation, coherence, and faith. We will end the module with a look at the relation between epistemic norms and moral norms.
In Aristotle's epistemology, the source of new knowledge is intuition, the grasping of the universal. As we saw, Aristotle held that intuitive knowledge is required in order to avoid an infinite regress. The modern philosophers generally accepted that there must be some kind of basic knowledge. But they proposed alternative accounts of just what that basic knowledge amounts to.
Aristotle had made sense-perception the basis of intuition, but the act of intuiting itself was intellectual on his account. The modern philosophers (up to Kant) rejected the idea that the intellect grasps the universal in the particular ("intuitive induction"), while holding on to the notion that intuition is intellectual in some way.
The most famous advocate of intellectual intuition was Descartes. For him, basic knowledge arises from "clear and distinct perceptions." Among the items which are clearly and distinctly perceived are simple truths of mathematics and various "common notions" of metaphysics. There is also clear and distinct perception of the fact of one's own existence, of the content of one's current thought, and of the properties of the mind. Descartes held that from this intuitive knowledge we can deduce the existence of God, and from the existence of God, we can deduce the existence and basic character of the physical world.
Descartes's "rationalist" successors Spinoza and Leibniz held similar views about the nature of intuition. Although they differed in the details about the nature of rational intuition, they appealed to it as a springboard to all other knowledge. A famous example of this is Leibniz's two fundamental principles: the principle of non-contradiction and the principle of sufficient reason. From these principles he deduced the existence of God and the basic character of the created universe.
The "British empiricists," particularly Locke and Hume, reacted quite differently to the fall of Aristotelian rational intuition. On their view, intuition can give us no substantive knowledge at all, but only knowledge of how our "ideas" are related to one another. If we want knowledge of "matters of fact" (as Hume put it in the Enquiry Concerning Human Understanding), it would have to be based ultimately on sense-perception or a reflective awareness of the operations of our minds.
Immanuel Kant, writing on the European continent in the generation after Hume, agreed with the empiricists's negative thesis. Any basic rational insight we might have reveals only "analytic" truths. Substantive, or "synthetic," truths are known in other ways. They are either known through experience itself, or else through a certain kind of argument about "conditions of possible experience." In the former case, the knowledge is "a posteriori," and in the latter it is "a priori."
In the wake of the empiricists and Kant, rational intuition has played a diminished role in accounts of knowledge. Most subsequent accounts of knowledge have been empiricist in character or else have taken more exotic forms that grow out of the work of Kant (such as that of Hegel and other "absolute idealist" philosophers.
There is a surprising amount of agreement between "rationalist" and "empiricist" philosophers concerning the possibility of knowledge through sense-perception. What most of them had in common was the view that sense-perception is indirect. A distinction is made between knowledge of the content of our minds, which is "immediate," knowledge of the existence and character of "external" objects which those states are supposed to "represent," which is "mediate."
Regarding the former kind of objects, it was generally agreed that there is no problem of knowledge. Knowledge requires certainty, and we can be certain about the contents of our own minds. According to Descartes, we have immediate perceptual knowledge in this way:
It is also the same "I" who has sensory perceptions or is aware of bodily things as it were through the senses. For example, I am now seeing light, hearing a noise, feeling heat. . . . I certainly seem to see, to hear, and to be warmed. This cannot be false; what is called "having a sensory perception" is strictly just this, and in this restricted sense of the term it is simply thinking. (Second Meditation)The Port-Royal Logic puts the matter thus:
It is equally impossible to doubt our perceptions: I am certain that I think I see the sun and the earth, whether or not there be any such things. . . . By confining ourselves to our own minds and considering only what transpires there, we find many instances of clear knowledge concerning which it is impossible to doubt. (Part IV, Chapter 1).In both cases, we know something about the way objects such as the sun seem or appear to be.
For these rationalist philosophers, judgments about external objects do not yield knowledge on the basis of sense-perception alone. There is always some uncertainty with respect to whether the perceptions of sense accurately describe the objects which they seem to present. If there is to be knowledge of those objects, this uncertainty must be overcome, and it is overcome only through the use of reason, as Plato had argued in the Theaetetus.
The Platonic insistence on a central role for reason in knowledge was echoed in Christian Platonist thinkers such as St. Augustine. Thus Arnauld wrote that, "St. Augustine was right to hold with Plato that judgments concerning truth and the rules for its discernment belong not to the senses but to the mind." Similar views can be found in Descartes, particularly in the famous example of the piece of wax in the Second Meditation. Descartes further held, notoriously, that one must first use reason in order to prove that God exists before one can know that external objects exist.
For the "empiricist" Locke, "There can be nothing more certain than that the idea we receive from an external object is in our minds: this is intuitive knowledge" (An Essay Concerning Human Understnding, Book IV, Chapter II, Section 14). Here it must be noted that Locke was not pre-judging whether it comes from an external object or not.
But whether there be anything more than barely that idea in our minds; whether we can thence certainly infer the existence of anything without us, which corresponds to that idea, is that whereof some men think there may be a question made; because men may have such ideas in their minds, when no such thing exists, no such object affects their senses. (An Essay Concerning Human Understanding, Book IV, Chapter II, Section 14)As with the "rationalists," something more than the mere "having of ideas" is required for the degree of certainty required for knowledge of external objects.
For the most part, philosophers of the modern period held that knowledge is based either on rational insight or on sense-perception. We shall see in the discussion of the validation project that sense-perception as understood by the mainstream modern philosophers seems inadequate as the basis for the kind of certainty they required of knowledge. Our reasoning about our perceptions, it seems, can at best establish probability, and at worse cannot establish even that.
A number of Scottish philosophers, most notably Thomas Reid, held that skepticism cannot be avoided unless we appeal to a distinct source of knowledge, which they called "common sense." In its most generic form, common sense is simply good judgment. But more specifically (and here we now restrict our attention to Reid), it is described as assent to what is "self-evident." The self-evident includes what we have called objects of rational intuition. But it also includes a number of general principles regarding contingent states of affairs as well as some specific states of affairs themselves.
Among the self-evident general principles are the following:
Regarding specific self-evident facts about the world, Reid seems to have returned to the views of the ancients. We can have basic knowledge of objects we perceive, not just of the mental "ideas" themselves. The problem with the empiricist account of perception is that it does not recognize that there are no pure perceptions, but judgment is built into them all.
For example, one does not simply feel a pain. Rather, one judges that one has a pain in a part of one's body such as a toe, and one judges further that this pain is of a certain kind, say the pain of the gout. So "I have a gouty pain in my toe" is integral to the sensation of pain. The mind does not receive an "impression" which it subsequently judges to be connected to a part of the body and its condition. The sensation and the judgment are inseparable.
It should be added that these basic judgments are fallible. In cases such as those involving phantom limbs, a "self-evident" perception-judgment is false. For Reid, then, the "self-evident" is only justified (as we now say) prima facie. It can be overturned despite its naturalness.
Aristotle had thought of deduction as a means to obtain new knowledge from what is already known. Deduction is an appropriate tool because when used properly it never takes one from truth to falsehood. But this, its great strength, is its great weakness as well. Deduction does not provide any information in its conclusion beyond what is contained in the premises. It does nothing more than re-package existing knowledge, presenting it in novel combinations, to be sure, but making no other advance. As Locke put it, "a man knows first, and then he is able to prove syllogistically" (An Essay concerning Human Understanding, Book IV, Chapter XVII).
The modern epistemologists viewed logic as a tool of inference, something to be used. They were not interested in the mere fact that there is a logical connection between premises and conclusion, but in whether this connection has been established by reasoning. From the standpoint of knowledge, the value of deduction is that it passes the certainty of the premises on to the conclusion, thus generating derivative knowledge.
Thus the emphasis was on the process of deduction or demonstration. For Locke, demonstration generates "a constant, immutable and visible connection" (An Essay Concerning Human Understanding, Book IV, Chapter XV, Section 1). This description is in line with Descartes's explanation (in the unpublished Rules for the Direction of the Mind) of deduction as a string of intuitively grasped connections.
Deduction played a more important role in the epistemology of the "rationalists" than in that of the "empiricists." Rationalist philosophers took rational intuition to be the sole source of knowledge. They believed that intuition is an immensely fertile source, so fertile that what is spun out of it through deduction is sufficient to build a metaphysical system of the universe.
The "empiricist" philosophers, on the other hand, held that rational insight yields little or no information about the world outside our thoughts. Locke, after giving an example of how demonstration "causes" assent to a mathematical proposition, added a cautionary note.
Our knowledge, as has been shown, being very narrow, and we are not happy enough to find certain truth in everything which we have occasion to consider; most of the propositions we think, reason, discourse—nay, act upon, are such as we cannot have undoubted knowledge of their truth . . . . (An Essay Concerning Human Understanding, Book IV, Chapter XV)For Hume, deduction could at best establish the existence of "relations of ideas." He allowed that "in all demonstrative sciences, the rules are certain and infallible" (A Treatise of Human Nature, Book I, Part IV, Section 1). Interestingly, he also held that we are fallible in our application of deductive rules, coming to the unsettling conclusion that reasoning is inherently uncertain.
It was common for the modern philosophers to distinguish between knowledge and probability, where probability was a degree of certainty falling short of the standard for knowledge. We must, however, distinguish between what we now call probability, which is a quantitative notion, and plausibility.
Locke distinguished between knowledge, with its certainty, and "judgment," where there is only a presumption of the conformity of ideas to reality. One presumes that something is the case when it is "taken to be so before it certainly appears" (An Essay concerning Human Understanding, Book IV, Chapter XIV, Section 4). One sort of presumption is based on probability, which is the uncertain counterpart of demonstration.
On Locke's view, the presumption of probability comes close to certainty. After having noted the limitations of demonstration, which was quoted above, he added,
yet some of [the propositions we think and act upon] border so near upon certainty, that we make no doubt at all about them; but assent to them as firmly, and act, according to that assent, as resolutely as if they were infallibly demonstrated, and that our knowledge of them was perfect and certain. (An Essay concerning Human Understanding, Book IV, Chapter XV, Section 2)The general character of probability is to determine assent by "preponderancy, after due weighing of all the proofs, with all circumstances on both sides" (An Essay Concerning Human Understanding, Book IV, Chapter XVII, Section 6). Locke undertook to describe some rough norms for probabilistic reasoning.
He divided the grounds of probability into two types. The first is a "conformity" or coherence with what we already know, have observed, or have experienced. The second is the testimony of other people regarding their own observation and experience. The degree of assurance we get from probabilistic reasoning depends on the proportion of the grounds of probability to one another.
Locke gives a series of examples to illustrate the way this is supposed to work. He claims to have knowledge of a man walking on ice because he actually sees it. If he is told by someone that he saw a man walking on ice in the dead of winter, he is "disposed by the nature of the thing itself to assent to it; unless some manifest suspicion attend the relation of that matter of fact" (Book IV, Chapter IX, Section 5). The testimonial report conforms to his own experience, and there is no contrary evidence which would diminish its credibility.
There are also cases of testimony which does not conform to one's experience. Someone in the seventeenth century born in the tropics where it never freezes might reject altogether the testimony of someone who told him that people walk over hardened water. But if enough people whom he trusts tell him the same story, he might come to believe that it is true. Locke recounts the story of the King of Siam who deemed the Dutch ambassador, whose strange stories he had hitherto believed because of his esteem for him, a liar when told by him that an elephant can walk over hardened water.
Locke's account of probability is quite qualitative and vague. David Hume provided a much more detailed set of rules for probabilistic reasoning. Some of the rules were quantifiable, while others were not. An important point to keep in mind is that for Hume, a belief is a vivid perception, and so the probability of a belief is a measure of the degree of the vivacity of the perception. In contemporary terminology, Hume's account of probability is "subjective."
Before dealing with probability proper, that is, "that evidence which is still attended with uncertainty" (A Treatise of Human Nature, Part I, Book III, Section 11), we shall look at what Hume called "proofs." He defined proofs as "those arguments, which are derived from the relation of cause and effect, and which are entirely free from doubt and uncertainty." As examples of certainty based on proofs he gives "the sun will rise tomorrow," and "all men must die."
While it is conceivable that the sun will not rise tomorrow, the totality of our experience of new days finds the sun to have risen in all of them. Nor have we found a person sufficiently old as to undermine our experience of universal mortality. Moreover, we have causal explanations of the rising of the sun and the death of men. The use of the term "proofs" indicates that for Hume, the standard for regulating assent is the removal of real "doubt and uncertainty," as opposed to the hypothetical uncertainty that arises from considering mere possibilities.
As for probability proper, Hume distinguished between the probability of "chances" and the probability of "causes." The essential difference between them is that with causes, the mind is determined to a certain view of their effects, on the basis of their always occurring together, what Hume called "constant conjunction." With "chance," there is no constancy, and so the mind is indifferent between the various possible outcomes.
The degree of probability in cases of "chance" depends on the concurrence of possible cases. Suppose we have a six-sided die, with four faces showing one number and the other two a different number. Roughly, the image we have as the result of imagining the four faces is twice as strong as the one we get when measuring two faces. As a result, we are twice as convinced that one of the four faces will come up than we are that one of the two will come up.
The probability of causes has its basis in the real experience of conjunction of things of one kind and another. As we have seen, where there is no exception over a long run of associations, we can meet the standard of "proof." But if there are exceptions, uncertainty is introduced. In that case, the vivacity induced by the association is weakened to the degree that the exceptions occur. So the explanation of the probabilities of "chance" and of "causes" is at bottom the same.
Hume wrote much more about probability, including laying down a number of "rules by which to judge of causes and effects" (Treatise, Part I, Book III, Section 15). We will not look into these epistemic norms here. Later, we will examine Hume's famous argument to the effect that in a fundamental way, none of our probable reasoning is justified.
The most powerful intellectual development during the modern period was the rise of modern science. The same philosophers who were responsible for the many breakthroughs in our understanding of the material world were also shaping the contours of epistemology. This was not an easy task for either the "rationalist" or the "empiricist."
The dominant mode of explanation in modern science was the use of mathematical modeling to explain observed phenomena. There was a long tradition in astronomy of explaining the motions of the heavenly bodies through complicated motions of perfect circles. But the Ptolemaic model broke down in the face of increasingly detailed observations: it did not make the right predictions.
The models used by Copernicus and especially Kepler proved to be strikingly effective in "saving the phenomena," that is, in making predictions that conformed to observation. Ultimately, Newtonian physics provided a comprehensive account of motion both near the earth and in the heavens.
In other fields, such as optics, mathematical models were put to use as well. But they did not all meet with the same success as did Newtonian physics. (This holds for Newton's own optics as well!) Another problem was that of underdetermination by the data. For example, Tycho Brahe introduced a model of the solar system in which the earth is at the center which gave the same results as the Copernican system.
On the side of the rationalists, the chief problem was that the intuition-deduction account of knowledge does not seem to apply to our investigation of the world, once the Aristotelian metaphysics of forms has been abandoned. One of Galileo's chief objections to Aristotle's practice of science was its indifference to empirical data that contradict what is supposed to be "scientific knowledge."
Yet Galileo himself was so confident of his own claims to scientific knowledge that in one place he boasted that he did not need to verify his conclusions observationally. In Dialogues concerning the Two Chief World Systems, the spokesman for the Aristotelians, Simplico, cites an experiment in which a ball dropped from the mast of a moving ship falls some distance away from the foot of the mast. Galileo's mouthpiece, Salviati, contends that in fact the ball would land at the foot of the mast, just as it would on a ship at rest. He admits that he has never made the experiment himself: "Without experiment, I am sure that the effect will happen as I tell you, because it must happen that way."
Descartes relied heavily on geometrical modeling in his scientific investigation. He was unable to give intuitive-deductive justifications for his results, but instead acknowledged that his reasoning relied on "suppositions" which might not hold in reality. And when he did provide deductive arguments for his claims about nature, they hardly inspired certainty. A case in point was his attempt to prove a law of the conservation of motion from the immutability of God.
Scientific explanation also presented difficulties for the "empiricists." They as well as the "rationalists" were faced with the problem of assimilating the use of mathematical explanation into their epistemological framework. For example, the "corpuscularian hypothesis" relies heavily on analogy between what is observed and unobserved. It is questionable how such analogies can be justified on the basis of sensory observation.
A second problem for the empiricists was to understand the status of causal laws. The rationalists, at least, could appeal to God as the source of laws of nature, since they claimed to know that God exists from intuition and deduction. No such appeal could be made by the empiricists, for whom proving the existence of God from experience was itself problematic.
Perhaps the best justification of mathematical explanation can be found in Newton. Newton proposed a number of normative principles for the conduct of scientific investigation, which he called "rules of reasoning in philosophy" (Principia Mathematica, Book III). One such rule, which is widely used in the practice of science, is to adopt the simplest explanation possible, i.e., to admit only as many causes as are required to explain the appearances. He also held that explanations should be as uniform as possible. Finally, he endorsed the use of induction to generalize from the results of "experiments" on some bodies to all bodies whatsoever.
Although his system of the world contained a great deal of mathematical idealization, he held that the mathematical formulas that result can be justified by an inductive method of "analysis." This method proceeds "from compounds to ingredients and from motions to the forces producing them, and in general from effects to their causes and from particular causes to more general ones, till the argument end in the most general" (Questions from the Optics, Question 30).
The following is a description of how the method is supposed to work.
This analysis consists in making experiments and observations, and in drawing general conclusions from them by induction, and admitting of no objections against the conclusions but such as are taken from the experiment, or other certain truths. For hypotheses are not to be considered in experimental philosophy. And although the arguing from experiments and observations by induction be no demonstration of general conclusions, yet it is the best way of arguing which the nature of things admits of, and may be looked upon as so much the stronger by how much the induction is more general. And if no exception occur from phenomena, the conclusion may be pronounced generally. (Questions from the Optics, Question 30)The key difference between this method and Aristotle's is that there is no claim to an intuitive grasp of the universal, and there is no claim to certainty. Newton was a fallibilist with respect to scientific theorizing. Indeed, he was sensitive to the possibility of "any exception [that] shall occur from experiments," and in the end it was just such exceptions that doomed his theory.
Coherence
Most of the modern philosophers considered coherence to be an important epistemic norm. For Descartes, it is can even result in knowledge, in spite of the fact that it is not based on intuition and deduction.
Most famously, after having tried to prove that God exists and is no deceiver, Descartes appealed to coherence as a criterion for distinguishing between waking and dreaming. "For I now notice that there is a vast difference between the two, in that dreams are never linked by memory with all the other actions of life as waking experiences are" (Meditations on First Philosophy, Meditation Six).
The reports of the various cognitive faculties reinforce one another:
And I ought not to have even the slightest doubt of their reality if, after calling upon all the senses as well as my memory and my intellect in order to check them, I receive no conflicting reports from any of these sources."The reason that the coherence of the information gives rise to knowledge is that our faculties are given to us by God, and "from the fact that God is not a deceiver it follows that in cases like these I am completely free from error."
Other philosophers, such as Berkeley and Kant, incorporated coherence as an essential norm for regulating assent to information about the physical world. But until more recent times, there was no real exploration of the nature of coherence or why it should provide justification.
Most of the modern philosophers had to find some way to accommodate faith as a basis for assent. As we saw in the last module, Arnauld had defined faith as assent based on the pronouncements of authority. This definition by a Catholic philosopher would be rejected by Protestant philosophers who reject the authority of the Catholic Church.
Deciding rationally who qualifies as an authority is a difficult issue regarding religious belief, though it may not be so hard in areas where competence can be demonstrated empirically. Locke's account of faith takes the issue head-on. As opposed to reason, faith is
the assent to any proposition, not thus made out by the deductions of reason, but upon the credit of the proposer, as coming from God, in some extraordinary way of communication. This way of discovering truths to men, we call revelation. (An Essay concerning Human Understanding, Book IV, Chapter VIII, Section 2)The remaining problem is how to determine the "credit of the proposer." How can we tell which persons with whom God has communicated directly? This is a question to be decided rationally, through probable reasoning.
Whatever God hath revealed is certainly true: no doubt can be made of it. This is the proper object of faith: but whether it be a divine revelation or no, reason must judge; which can never permit the mind to reject a greater evidence to embrace what is less evident, nor allow it to entertain probability in opposition to knowledge and certainty. (An Essay concerning Human Understanding, Book IV, Chapter XVIII, Section 10)Locke's subordination of faith to reason is widely accepted in the contemporary secular society of the West.
David Hume took the matter even further, by investigating in detail the limits of probable reasoning in determining religious truth. Hume's target was notion that nature itself is a revelation of God's existence and nature. In his Dialogues concerning Natural Religion and some sections of his Enquiry concerning Human Understanding, Hume argued that probabilistic reasoning from natural phenomena is too weak to compel our assent to any but the most vague descriptions of a divine being.
John Locke claimed that we can have "sensitive knowledge" of external objects. As noted above, he lowered the standard for knowledge from absolute certainty to what Descartes called "moral certainty."
It is evident that the mind knows not things immediately, but only by the intervention of the ideas it has of them. Our knowledge, therefore, is real only so far as there is a conformity between our ideas and the reality of things. (An Essay Concerning Human Understanding, Book IV, Chapter IV, Section 3).Locke held that in the case of "simple" or "uncompounded" ideas, there is such a conformity. The simple ideas, he held, cannot be produced by the mind itself, and so
must necessarily be the product of things operating on the mind, in a natural way, and producing therein those perceptions which by the Wisdom and Will of our Maker they are ordained and adapted to. From whence it follows, that simple ideas are not fictions of our fancies, but the natural and regular productions of things without us, really operating upon us; and so carry with them all the conformity which is intended; or which our state requires: for they represent to us things under those appearances which they are fitted to produce in us: whereby we are enabled to distinguish the sorts of particular substances, to discern the states they are in, and so to take them for our necessities, and apply them to our uses. Thus the idea of whiteness or bitterness, as it is in the mind, exactly answering that power which is in any body to produce it here, has all the real conformity it can or ought to have, with things without us. And this conformity between our simple ideas and the existence of things, is sufficient for real knowledge. (An Essay concerning Human Understanding, Book IV, Chapter IV, Section 3)One can see in these remarks a foreshadowing of externalism. We have knowledge from simple ideas by simply virtue of the way they are produced in the mind by bodies, with no evaluation required. What gives us the certainty of knowledge is that the ideas are produced by faculties which function in a way to assure conformity. If this is correct, then we have an externalist account, albeit a limited one, of perceptual knowledge.
It is true that Locke went on to give arguments to show that we have no grounds for doubting the veracity of our simple ideas because they may fail to conform to reality. These arguments are said to show that "we are provided with an evidence that puts us past doubting" (An Essay Concerning Human Understanding, Book IV, Chapter II, Section 14). But this is just Locke carrying out the epistemological process of validation. He gives no indication that such reflection is required for there to be knowledge in ordinary cases, as it may seem Descartes demands.
Epistemic Norms and Practical Norms
The chief interest of the ancient Stoics and skeptics was the regulation of assent. They wanted to know the conditions under which one ought to assent to (as we would now put it) the truth of a proposition. We saw that Carneades considered assent in a practical context, holding that the standards for assent vary with the practical consequences assenting rightly.
Blaise Pascal, a contemporary of Descartes, gave a quantitative formulation of the relation between assent and its consequences. The case he considered has come to be known as "Pascal's Wager." We will not discuss the details of the wager here, but the important point is that Pascal devised a means of assessing the rationality of a choice in a way that is partially independent of probability. Specifically, Pascal claimed that it may be rational to assent to a proposition (that God exists) even if we have no idea how probable the truth of that proposition might be.
Pascal had the germ of a measure of rationality we now call "expected utility." The expected utility of an action is a function of the probability and the value of its outcomes. For a nice presentation of how this works, see Josh Parson's slide presentation. By comparing the expected utilities of different decisions, one can arrive at a rational measure of their their advisability. Where the decision is what to believe, expected utility can be used as a standard to regulate assent.
Deontology
Some of the writings of Descartes and Locke associate regulation of assent with moral responsibility. The discussion takes place in the context of a theological assumption, that human beings were created with the faculties they have by God. It is also assumed that there is a right and wrong use of those faculties. The right use is to strive to assent to the truth, and the wrong use is to assent rashly or irrationally. It is our duty to reason well and a transgression of our duty to reason poorly.
In a sense, Descartes's main epistemological project was to discover a method by whose use we can be completely certain that we have avoided error. Having validated the intuition-deduction method as infallible, he concluded in the Fourth Meditation that so long as that method is used rightly, there is no reason for one ever to make a mistake. For this reason, we cannot in any way describe God as a deceiver or blame God for not preventing us from falling into error.
According to Locke, one should believe or disbelieve "according as reason directs him" (An Essay concerning Human Understanding, Book IV, Chapter XVII, Section 24). One may miss the truth when so doing, but one will at least have the satisfaction of carrying out his duty. On the other hand,
He that believes without having any reason for believing, may be in love with his own fancies; but neither seeks the truth as he ought, nor pays the obedience due to his Maker, who would have him use those discerning faculties he has given him, to keep him out of mistake and error. (An Essay concerning Human Understanding, Book IV, Chapter XVII, Section 24).Locke seems to have been motivated in adopting this view by the desire to show that there can be no conflict between faith (which is also obligatory) and the use of reason.
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