class: center, middle, inverse, title-slide .title[ # Knowledge of the External World ] .date[ ### MSA 2025 ] --- class: middle, center # Epistemology The study of knowledge, including its nature and extent. --- # Question Philosophers debate whether we can acquire knowledge about the world through observation. Some argue that it is impossible to know anything about reality since we can never directly experience it (our only access is through our senses). Which of the following best characterizes your view? a) The universe is a physical reality that we can comprehend through science and observation. b) We cannot obtain any knowledge about reality. --- # Question 2 Can we _know_ anything about the world via our senses? - If you think we do, you are a **EXTERNAL-WORLD REALIST**. - If you think we don't, you are a **EXTERNAL-WORLD SKEPTIC**. --- class: medium-font # External-world skepticism .pull-left.w40[ <img src="assets/apple.png" alt="" height="350"/> ] .pull-right.w60[ Your sensory experience helps you discriminate between the following possibilities: - This is an apple and not a door. - This is an apple and not a flower. - This is an apple and not an orange. ] --- class: medium-font # External-world skepticism .pull-left.w40[ <img src="assets/brain-in-vat.jpg" alt="" height="350"/> ] .pull-right.w60[ Your sensory experience helps you discriminate between the following possibilities: - This is an apple and not a door. - This is an apple and not a flower. - This is an apple and not an orange. But your sensory experience _does not help you_ discriminate between the following possibilities: - This is a real apple. - My brain is really in a bucket connected to a computer, which is feeding me the experience of an apple (so there's no apple). - I'm having a very vivid dream of seeing an apple in an MSA class (but there's no MSA class). ] --- # Discussion questions 1 1. Why does Descartes choose to doubt everything he previously believed? 2. What kind of beliefs does Descartes doubt first, and why? -- 3. Why does Descartes switch from considering the hypothesis that he might be dreaming to considering the hypothesis that God, or an evil demon, is deceiving him? 4. Does Descartes think he cannot doubt that `\(2 + 3 = 5\)`? 5. Do you think there’s a limit to doubt — or is everything doubtable? Explain your view. --- # Doubting experience 1. It could be that my sensory beliefs about my current surroundings are true because my senses accurately reflect the world, or it could be that my sensory beliefs are false because I’m asleep and dreaming. 2. I have no firm reason to believe that my sensory beliefs arise in one way rather than the other. 3. If we are faced with two mutually exclusive hypotheses and we have no reason to prefer one over the other, then we cannot know which is true. 4. Therefore, I have no knowledge of my current surroundings. --- # Doubting reason 1. It could be that my logical beliefs are true because reason guides me, or it could be that my logical beliefs are false because an evil demon is deceiving me. 2. I have no firm reason to believe that my logical beliefs arise in one way rather than the other. 3. If we are faced with two mutually exclusive hypotheses and we have no reason to prefer one over the other, then we cannot know which is true. 4. Therefore, I have no knowledge of logical matters. --- # The skeptical argument 1. It could be that either `\(P\)` or `\(\neg P\)` is the case. 2. You do not have the means to discriminate between `\(P\)` and `\(\neg P\)`. 3. If it could be that `\(P\)` or `\(\neg P\)` and you do not have the means to discriminate between `\(P\)` and `\(\neg P\)`, then you do not know `\(P\)`. 4. Therefore, you do not know `\(P\)`. --- exclude: true ### The skeptical argument Where `\(S\)` is a subject, `\(s_p\)` is a skeptical possibility, such as being in a dream, and `\(q\)` is a claim about the world: 1. If `\(S\)` doesn't know that `\(\neg s_p\)`, then `\(S\)` doesn't know that `\(q\)` 2. `\(S\)` doesn't know that `\(\neg s_p\)` 3. Therefore, `\(S\)` doesn't know that `\(q\)` ### Moorean shift 1. If `\(S\)` doesn't know that `\(\neg s_p\)`, then `\(S\)` doesn't know that `\(q\)`. 2. `\(S\)` knows that `\(q\)`. 3. Therefore, `\(S\)` knows that `\(\neg s_p\)`. --- # Vogel and Explanationism Discussion questions: 1. What is the underdetermination principle? 2. What is the example of the gas gauge supposed to show? 2. What is the minimal skeptical hypothesis? Why is it not as good as our ordinary beliefs about the world? 3. What's the problem with the Flat Earth story in explaining the roundness of the Earth? 4. Which of the two failings is supposed to afflict the isomorphic skeptical hypothesis? --- # Inference to the Best Explanation 1. I observe that `\(P\)`. 2. A series of explanations — `\(E_1, E_2, E_3, ... , E^*\)` — could account for `\(P\)`. 3. Of all these explanations, `\(E^*\)` is the best one. 4. Therefore, `\(E^*\)` is true. Example: 1. I observe a stream of water dripping from my ceiling. 2. A number of explanations could account for this: I have a hole in the roof, there’s a rain cloud in the attic, or my wife is pouring water into the attic as a prank. 3. Of these explanations, the best one is that I have a hole in the roof. 4. Therefore, I have a hole in the roof. --- # Good Explanations 1. **Explanatoriness**: Good theories explain all the facts that need explanation. 2. **Completeness**: Good theories are complete and do not raise further questions. 3. **Power**: They can explain many other phenomena, not just one. 4. **Modesty**: They don't claim any more than is needed to explain the observed facts. 5. **Simplicity**: They invoke fewer parts, entities, or process. 6. **Conservativeness**: They don't challenge other beliefs we have. --- # Explanatoriness Good theories explain all the facts that need explanation. - Good example: Germ theory explains both symptoms and transmission of disease. - Bad example: “Evil spirits cause sickness”—this leaves many facts (like contagion) unexplained. --- # Completeness Good theories are complete and do not raise further questions. - Good example: Plate tectonics explains the formation of mountains, earthquakes, and volcanoes without needing additional assumptions. - Bad example: “Mountains are big because they grew”—this leaves us wondering, How? What mechanisms cause them to grow? --- # Power Good theories can account for many other phenomena, not just a single observation. - Good example: Natural selection explains the adaptation of species across a range of environments. - Bad example: “This particular finch’s beak is short because it fell from a tree”—this cannot account for other birds’ beaks. --- # Modesty Good theories do not claim more than is needed to account for the facts. - Good example: “Bacterial resistance evolves due to mutations and natural selection” (without adding additional, unfounded mechanisms). - Bad example: “Bacterial resistance evolves due to mutations, plus a universal moral decline”—this introduces needless elements. --- # Simplicity Good theories invoke fewer parts, entities, or processes. - Good example: “Lightning occurs due to a discharge of static electricity between clouds and the ground.” - Bad example: “Lightning occurs due to a team of thunder gods battling in the clouds”—this adds additional, needless entities. --- # Conservativeness Good theories do not conflict with or undermine well-established beliefs we already hold. - Good example: "Viruses cause the flu"–this is consistent with extensive medical knowledge about contagion and the immune response. - Bad example: "The flu is sometimes caused by Halloween"–this disregards a vast body of scientific understanding about disease mechanisms and conflicts with well established beliefs. --- # Limits of IBE 1. I observe that `\(P\)`. 2. A series of explanations — `\(E_1, E_2, E_3, ... , E^*\)` — could account for `\(P\)`. 3. Of all these explanations, `\(E^*\)` is the best one. 4. Therefore, `\(E^*\)` is true. - It is a comparative process, it can only select the best hypothesis currently available. - The fact that an explanation has some of the features discussed does not guarantee that is the correct explanation. - Although it is rare, complex, shallow, or non-conservative explanations can be true. - However, in absence of more evidence, one is justified in believing the explanation that exhibits more of these features.