The medieval worldview was undermined in various ways during the Renaissance, Reformation, and Counter Reformation movements of the 16^th century. The science or wisdom of the Middle Ages was based on three sources: Aristotle, Reason, and Theology. The reliability of each of these comes under attack in various ways in the 16^th century. Since each of these represented a kind of foundation on a pyramid structure of human knowledge, these attacks created cracks in the foundations of the Western intellectual tradition.

1. The authority of Aristotle was put into question with the rise of a new science, specifically the new physics and scientific methodology of scientists such as Copernicus and Galileo. The critique of geocentric cosmology is an important example of the sort of challenges put to the old science rooted in the Greek tradition.
2. The authority of reason was put into question with the rise of various forms of skepticism during the Renaissance. Various skeptical arguments had existed in Greek philosophy subsequent to Aristotle. Since the Renaissance involved a revival of classical culture, it also brought into circulation various writings by Greek skeptics (e.g., Sextus Empiricus). One of the Descartes' contemporaries, Montaigne, was an important defender of skeptical arguments. One of Montaigne's central claims was that all we could "know" are appearances, not the real nature of things.
3. The authority of theology was put into question with the rise of the Reformation and its challenge against the Roman Catholic ecclesiastic authority. Also, the Reformation itself quickly became a very diverse and pluralistic movement, further raising doubts about whether theological ideas based on the Bible could serve as an authority since there were so many different interpretations of the Biblical text.

A + B + C = an epistemological crisis for the Western world. It is this crisis that Descartes aims to resolve.

Descartes' project was to find a secure foundation for the sciences or knowledge. His project was not simply to fix the foundations, but to actually establish a new foundation.

1. Descartes' method of establishing a new epistemological foundation begins with "Methodological doubt." Descartes begins with the general destruction of his former opinions with the hope to see what opinions or beliefs can be left standing after subjecting all his opinions to rigorous philosophical critique.
2. Descartes argues that methodological doubt need not require proving that all his beliefs are false, but only that they are not certain or indubitable. Nor does he aim to examine each of his beliefs individually to arrive at a general conclusion about his beliefs. He aims to examine the sources of belief or principles by which we learn. If these sources or principles are questionable, then there will be doubt also about the beliefs we derive from them. The sources will be question just if they are not reliable sources or we have adequate reason to suppose that they are not reliable. (More technically, Descartes is thinking about whether there can be grounds for doubting that certain alleged sources of knowledge actually and normally produce true beliefs.)
3. The source of most of our beliefs is sensory experience. At any rate, nearly all our beliefs about the external world arise directly or indirectly from sense experience. Descartes also recognizes reason as a source for some knowledge (such as mathematical knowledge and logic). See below for how this relates to his skeptical arguments.
4. Certainty and Indubitability: Descartes is not thinking of a mere psychological certainty or the idea that something cannot, as a point of cognitive psychology, be doubted. There are many things that we may be quite sure of, but which there may be good reason for not being so confident about. Descartes is concerned with certainty and indubitability as normative qualities of beliefs. A belief is certain for Descartes only if there are no (good) grounds or reasons for doubting it. Objectively and epistemically speaking, the belief cannot be subject to doubt.

We can state Descartes general line of reasoning as follows:

1. If we know some proposition p, then we are certain of p.
2. If we are certain of p, then there are no grounds for doubting p.

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3. Therefore, if we know some proposition p, then there are no grounds for doubting p.

As stated above Descartes does not intend to examine all of his beliefs individually. Rather he wants to examine the principles or sources by which we "allegedly" know most of what we believe, and everything that we believe about the external world.

Thus he employs another premise:

4. If we have grounds for doubting the reliability of the source or principle under which we believe some proposition p, then we have grounds for doubting all p-type beliefs.

Descartes seeks to develop a case for denying the consequent of (3). He seeks to show that there are grounds for doubting sensory perceptual beliefs. Descartes presents two skeptical arguments. They each involve postulating a situation that (a) if actual would undermine our having knowledge and (b) if possible presents a ground for doubting whether we in fact have knowledge. Hence, these argument aims to deny the consequent in the conditional statement in (3) above, and thereby deny the antecedent. Hence, he derives the conclusion: we do not know p. And he will get a universal doubt about all our empirical knowledge by virtue of such skeptical arguments entailing the antecedent of (4), from which it follows that we should affirm the consequent.

Moreover, the arguments aim to undermine not just every particular belief individually, but in one swoop, but raising doubts about the reliability of the source of all our beliefs about the external world.

1. The Dream Argument:

The dream argument claims that we have no way of determining conclusively at any moment whether or not we are dreaming. Hence, it is possible at any given time that we are dreaming. Descartes thinks that this mere possibility is sufficient to undermine knowledge. Why? The most likely reason is that Descartes assumes something like: if we were dreaming, then beliefs about the external world produced in us by our dreams would tend not to be true. (See Stroud article).

2. The Evil Demon Argument:

Objection 1: Surely the information/imagery that comes to us in our dream state must have initially come from somewhere, therefore there must be a reality somewhere that we have experienced and that provides the source of the material out of which are dreams are fashioned.

Response: Descartes' argument is logically consistent with this objection. Descartes is not asserting or implying that there is no reality or no reality that is the source of data and imagery in our dreams. His only point is that we can't conclusively determine at any moment whether we are in a state that involves being in touch with reality or a dream-state in which we are simply utilizing the information acquired from our waking state, when we are allegedly in touch with reality.

Objection 2: The dream argument assumes that Descartes knows that there is a difference between when we are awake and when we are dreaming, and that latter is not conducive to the production of true beliefs. But he could not know that there is such a distinction unless he had some empirical knowledge, i.e., knowledge about external reality.

Response: There are two possible responses here. (1) Descartes assumes that we recognize a difference in our experience between two different states. This is simply a truth about our own mental life. Furthermore, on the grounds of the incompatibility and discontinuity of what these experiences report to us, he takes it to be rather obvious that they can't both be consistently supplying us with truths about the external world. This belief of Descartes would not have to be derived from sense experience, as it is a purely logical matter as to whether the experiences we have or report about ourselves having are consistent with each other. (2) Descartes is simply postulating a possible state of affairs, which he calls dreaming, which is such that if it were actual we would not know any of the beliefs that come to us through that state. This is a purely conceptual point and does not itself depend on sense experience. The fact that he identifies the state in question with dreaming is largely a dialectical point since he knows that people hold these beliefs about their experience. But it does not seem that any of the premises in his argument actually demand that he acquire them from experience at all.

Objection 3: For all Descartes knows our dreams do put us in touch with reality. Hence, Descartes is not rationally entitled to assume in his argument that such a source of belief would not be unreliable.

Response: Descartes need not deny that our actual dream states put us in touch with reality. His position only requires that what he describes as "dreams" do not consistently put us in touch with reality of the external world, and that it is possible that such a state is actual. How does he know any of this? As I said above, I think Descartes can argue that it is largely a conceptual point. He has proposed a possible situation, which he calls dreaming, which if actual would not reliably produce true beliefs about the external world. The normal account of dreaming and what is typically understood typically understood by "external world" would certainly be sufficient for establishing this. It matters not whether Descartes correctly describes what actually happens to us. It matters not whether someone has a different definition of what a dream involves. Descartes is simply describing a possible situation in which beliefs, even if they happened to turn out true, would not constitute knowledge.

(1) The Scope of Skepticism

Each of the responses above works only if Descartes is seeking to raise doubts only about our empirical knowledge. In that case, he can draw on truths of reason (e.g., mathematics, logic) to establish skepticism. In fact, any "argument" that aims to produce "grounds" for doubting must assume something that is not subject to doubt. Otherwise one could simply

doubt whether one has produced any ground for doubt in the first place.

It is generally believed that Descartes' second skeptical argument does not merely reinforce the first one by raising doubts about the external world, but that it, unlike the dream argument, actually raises doubts about other sorts of belief the truth of which would not be undermined by the possibility that one is dreaming. For instance, Descartes appears to think the possibility of our dreaming would not undermine our mathematical beliefs or other purely conceptual beliefs. But if such beliefs were produced by a deceiving all-power being, they would not constitute knowledge, even if they happened to be true. But surely this situation is possible. Hence, we have grounds for doubting more than just our empirical beliefs.

This move establishes a more global skepticism, but it also raises doubts about the coherence of Descartes' project from the start. Is it coherent to believe that every belief is subject to doubt, especially since Descartes proposes to withhold belief in everything for which there is ground to doubt? Would this not apply to his own argument? Can Descartes' arguments escape self-defeat? If not, we are not rationally obliged to accept them.

(2) Descartes' Assumption about Knowledge

Descartes equates knowledge with certainty. From here he is able to argue that if we cannot eliminate the possibility that we are mistaken, then we do not know. But is he correct about knowledge requiring certainty? This is a criticism to which we will return at several points throughout the course.