3.  According to philosophical skepticism, we can’t have knowledge of the external world.

4.  Knowledge by acquaintance (knowing what)— experiential knowledge.  Performative knowledge (knowing how)—skill knowledge.  Propositional knowledge (knowing that)— factual knowledge.

5.  Rationalism is the doctrine that reason is the only source of knowledge of the external world.  Empiricism is the doctrine that sense experience is the only source of knowledge of the external world.

6.  An a-priori proposition is one that can be known prior to or independently of sense experience.  An a-posteriori proposition is one that can only be known after one has acquired sense experience.

7.  An analytic proposition is a logical truth or one that can be turned into a logical truth by substituting synonyms for synonyms.  A synthetic proposition is a proposition that is not analytic.

8.  According to the correspondence theory, a proposition is made true by its correspondence to reality.  According to the coherence theory, a proposition is made true by its coherence with a system of beliefs.  According to the pragmatic theory, a proposition is made true by its practical consequences.

9.  According to cognitive subjectivism, a proposition is made true by ones believing it to be true.  According to cognitive cultural relativism, a proposition is made true by a society believing it to be true.  Objection: Both views are self- contradictory because a proposition and its negation could be believed to be true.

10.  The doctrine that a proposition is true if and only if things are as it says they are.  This preserves the insight that true propositions accurately represent reality without falling prey to the criticisms that were fatal to the other theories of truth.

11. Skepticism about Skepticism

12.  Heraclitus maintained that identity over time is an illusion. He thought that the world was being created anew each instant.  “You cannot step into the same river twice,” he proclaimed, “for the water into which you first stepped has flowed on.”

13.  Parmenides thought that reality must contain a continuing substance, because only that which is unchanging is real.  He reasoned that nonexistence (nothingness) cannot exist.  Therefore, everything that exists must always have existed.  From nothing, nothing comes, and nothing cannot come from something.

14.  Paramenides believed that because nonexistence cannot exist, it cannot be thought about.  Do you agree? Can you think about nothing? That is, can nothingness be the object of your thought?  If so, can you describe what you’re thinking about when you’re thinking about nothing?

15.  In this stadium, before you reach the door you must reach the point halfway there. But before you reach the halfway point, you must reach a point halfway to that.  Since it takes some finite interval of time to move from one point to another, and there are an infinite number of halfway points, it would take you an infinite time to pass through them all and get out.

16.  Plato, following Parmenides, held that only that which is unchanging is real, and, following Heraclitus, that what is presented to our sense is constantly changing.  He concluded that what we sense isn’t fully real.  The prisoners in the cave see only the shadows cast by the truly real objects: the “forms.”

17.  British philosopher Nick Bostrom thinks there is a good probability that we’re living in a computer simulation.  Do you think that Bostrom’s simulation argument is a good one? That is, do you think it is probable that you are living in a computer simulation? Why or why not?

18.  Do you think that there are any concepts or truths that all normal humans have or know?  If so, what are they?

19.  Descartes doubted that sense experience can give us knowledge because knowledge requires certainty and nothing we learn through our senses is certain.  Descartes holds that you are justified in believing something to be true only if you are certain of it.

20.  How often has it happened that you thought something was real only to find out that you were dreaming?  Can you know for certain that you’re not dreaming right now?

21.  Suppose that every dream you had ended by your getting into bed and going to sleep.  Would you be able to tell what was a dream and what was reality? How?

22. 1. We can’t be certain that we’re not dreaming. 2. If we can’t be certain that we’re not dreaming, we can’t be certain that what we sense is real. 3. If we can’t be certain that what we sense is real, we can’t acquire knowledge through sense experience. 4. Therefore, we can’t acquire knowledge through sense experience.

23.  Suppose that an evil genius used telepathy (or a mad scientist used electrodes) to put false ideas into your mind.  Can you be certain that you’re not under the influence of such a person right now?  If not, can you have knowledge of the external world?

24. 1. We can’t be certain that our sense experience is not caused by an evil genius. 2. If we can’t be certain that our sense experience is not caused by an evil genius, we can’t be certain that what we sense is real. 3. If we can’t be certain that what we sense is real, we can’t acquire knowledge through sense experience. 4. Therefore, we can’t acquire knowledge through sense experience.

25.  Descartes cannot doubt that he is thinking, for doubting is a type of thinking.  And Descartes can’t doubt anything unless he exists.  So Descartes claims that he can be absolutely certain of one thing, namely, “I think, therefore I am.”

26.  Descartes knows the contents of his mind; if he seems to see a tree, he knows that he seems to see a tree.  To acquire knowledge of the external world, he needs a principle to bridge the gap between appearance and reality.

27. 1. God exists and is no deceiver. 2. If God exists and is no deceiver, then whatever I clearly and distinctly perceive is true. 3. Therefore, whatever I clearly and distinctly perceive is true.

28. 1. I clearly and distinctly seem to see a tree in front of me. 2. Whatever I clearly and distinctly perceive is true. 3. Therefore, there is a tree in front of me.

29.  Descartes can’t know that God exists and is no deceiver unless he knows that what he clearly and distinctly perceives is true.  But he can’t know that what he clearly and distinctly perceives is true unless he knows that God exists and is no deceiver.

30.  Foundationalism maintains that there are basic beliefs, that is, beliefs whose justification does not depend on other beliefs.  Also, it maintains that the justification of all other beliefs depends, at least in part, on the basic beliefs  The problem of the Cartesian circle faces anyone who takes a foundationalist approach to knowledge.

31.  The fact that we ordinarily claim to know many things that aren’t certain casts doubt on the claim that knowledge requires certainty.  But if it’s doubtful that knowledge requires certainty, then Descartes can’t know that knowledge requires certainty.

32.  To know a proposition, it doesn’t have to be established beyond a shadow of a doubt. It only has to be established beyond a reasonable doubt.  This is the standard that is used in courts of law to adjudicate matters of life and death; it can also be used to adjudicate matters of knowledge and ignorance.

33.  Empiricism leads to skepticism about anything that cannot be sensed.  Empiricists such as David Hume believe that only terms that stand for ideas derived from sense experience can refer to real objects.

34.  Induction assumes that the future will resemble the past.  What justifies our believing that?  If this belief must be accepted on faith, is science a religion?  Does hypothetical deduction (inference to the best explanation) suffer from the same problem?

35.  Kant noticed that some truths can be known without being empirically confirmed, but also are not true by definition.  According to Kant, to make sense of the world around us, we naturally categorize the world into a conceptual scheme.

36.  Are scientific laws invented or discovered?  The traditional view is that scientific laws exist “out there” in the world and that the job of the scientist is to discover them.  Kant, however, claims that “the order and regularity of the appearance we entitle nature, we ourselves introduce.” For him, reality is a human construct.  Which view do you think is correct? Why?