Probability and Rational Choice
(PHIL 258g, Fall 2021)
This course is about how to live with uncertainty. How should our beliefs be shaped by evidence about the world? How should we make decisions when our actions have risky outcomes? How can we trust other people in shared projects?
This course has five parts.
Thinking Clearly. How is your mind vulnerable to biases that lead you away from the truth? What skills and habits will help you have beliefs that aim at what is true and make choices that aim at what is good? Why bother with tables and numbers when it comes to real life questions?
Responding to Evidence. How should you change your mind as you learn new things? How can you have coherent beliefs even when you aren’t sure what is true?
Choosing Well. What should you do when you don’t know how things will turn out?
Philosophical Foundations. What justification is there for the standard rules of decision theory (from part 3), and the standard rules for degrees of belief (from part 2)? Do the standard rules sometimes give the wrong answers?
Working Together. Why is it hard to solve social problems together? What factors make it easier or harder to cooperate?
This is a philosophy class, but we will also use tools and ideas from psychology, math, and economics.
This class fills a quantitative reasoning general education requirement (GE-F). In some ways it will be like a math class. It involves numbers and equations, and there will be problem sets. But our main emphasis won’t be on calculation, but rather on conceptual understanding. How can we use probabilities to understand an uncertain world? What do they mean?
You will be evaluated not just on your ability to calculate correct answers, but also on your ability to think critically and write clearly.
This class does not assume you have any background in college-level math. But you will need to do some arithmetic. (For example, what is 2/3 of 3/5? What is 20% of 80?) And you will need to do some algebra. (For example, solve the equation 3p = p + 1 for p.) If you don’t remember how to do those things, you will need to do some review to brush up. This might be a helpful resource:
This class does not assume you have any background in philosophy. But you will need to think carefully, and you will need to write clearly and directly. If you need help with your writing, the USC Writing Center might be a helpful resource:
You will think carefully and critically about what you should believe and what you should do.
You will understand how cognitive biases can lead your beliefs away from the truth, and the habits of mind that can help compensate for them.
You will use probabilities to understand how beliefs fit together and are supported by evidence. You will use diagrams, numbers, and symbols to determine how strong evidence for a claim is, and when a theory is more likely to be true. You will identify mistakes and confusions in real-life reasoning with probabilities.
You will represent choices using diagrams, numbers, and symbols. You will use these tools to precisely describe difficult decisions, and to work out how to balance risks.
You will apply probability and decision theory to make progress on controversial philosophical questions.
You will precisely explain and evaluate philosophical arguments about what you should do and what you should believe. You will understand and explain the central mathematical ideas that these philosophical arguments rely on. You will clearly distinguish descriptive claims about what will happen from normative claims about what should happen.
You will represent cooperation problems using diagrams, numbers, and symbols. You will use these tools to precisely describe social relationships and explain special problems facing group decision-making.
We have two main textbooks for this class:
Reason Better is only available through the Top Hat platform, which is described below. Odds and Ends is available for free online, here:
We will also use some short selections from other books and articles, which I will distribute through the course Top Hat site.
We will be using Top Hat Pro (https://www.tophat.com) to access the digital interactive textbook, Reason Better, that we will be using in this class. We will also use Top Hat for in-class quizzes.
(This will cost you some money, but it’s quite a bit less than the price of the hard copy textbooks I used to use for this course, so I think it’s a fair deal.)
For instructions on how to create a Top Hat account and enroll in our Top Hat Pro course, please refer to one of the following resources:
If you already have a Top Hat account, go to https://app.tophat.com/e/139749 to be taken directly to our course. If you are new to Top Hat, follow the link in the email invitation you received or
139749The cost of the textbook will be applied at checkout when enrolling in our Top Hat course. Bear in mind that textbook material will be made available in our course throughout the semester once your professor assigns it to the class, so do not panic if you do not see any content in the course upon entry.
Should you require assistance with Top Hat at any time please contact their Support Team directly by way of email (support@tophat.com), the in-app support button, or by calling 1-888-663-5491. Specific user information may be required by their technical support team when troubleshooting issues.
| Lecture | Mon, Wed | 2–3:20pm | SOS B44 |
| Discussion Section | Tue | 8-8:50am | MHP 102 |
| Discussion Section | Tue | 9–9:50am | MHP 102 |
| Jeff’s Office Hours (one-on-one appointments) | Mon | 12:30–1:30pm | Zoom (use Calendly) |
| Jeff’s Office Hours (open session) | Wed | 12:30–1:30pm | MHP courtyard, maybe eventually STO 227 |
| Brian’s Office Hours | Tue | 11am–1pm | MHP courtyard, or Zoom by appointment |
| Final Exam | Fri, Dec 10 | 2–4pm | SOS B44 |
You can reserve a one-on-one appointment during Jeff’s Monday virtual office hours using this link:
You’ll get a Zoom link automatically after you sign up for a time.
If you have class conflicts with our scheduled office hours, you can email Jeff or Brian to try to find another appointment time that works.
Assignment deadlines and midterm dates are provisional: I may adjust these dates if necessary. Watch for updates.
| Reading questions (Top Hat) | 10% | Every meeting |
| Check-in quizzes (Top Hat) | 5% | Every meeting |
| Discussion activities | 5% | Weekly |
| Problem sets | 20% | See schedule |
| Modeling project part 1 | 5% | See schedule |
| Modeling project part 2 | 10% | See schedule |
| Midterm | 20% | See schedule |
| Final exam | 25% | Friday, December 10, 2-4 pm |
The grade break-down is structured to reward consistent work through the whole semester. No one component is worth a huge portion of your grade. Make sure to keep up with the reading questions, check-in quizzes, discussion activities, and problem sets. No single one of them is worth very much on its own, but all together they are worth 40% of your grade.
The later parts of this class will build on the skills you develop early on, so if you don’t keep up with the work consistently week by week, you may find yourself lost later on.
Each section of the assigned reading on Top Hat has a few review questions at the end. You should answer these when you do the reading before each class. But usually I will give you a grace period to answer reading questions (or change your answers) up to Friday at 5pm. (These deadlines will be posted on Top Hat.) In general, I will not give any extensions for reading questions beyond this grace period.
Normally, half of the credit for a reading question will be based on answering the question at all, and the other half will be based on whether you get it right.
We will use Top Hat for frequent short in-class quizzes. Usually these quizzes will just be one or two questions. We will have one of them (or sometimes more than one) in almost every class. Some of these will be standard quizzes, in which you only get points for correct answers, and some of them will be purely participation-based.
Discussion section is a required part of this class. Be present, be prepared, and be on time. Ask questions, contribute to discussions, and participate in activities. Be helpful and respectful to others.
Problem sets will include calculations, drawing diagrams, as well as short written reflections about philosophical questions. There will be five problem sets, spread out through the semester (see the class schedule).
Problem sets will be due at the beginning of class on the day of the deadline (2pm Pacific time). If you do not turn a problem set in at the beginning of class, you will use a late day (see the Late Policies below).
You will write an analytical essay applying tools from probability and decision theory to a philosophical or practical problem. This will have two parts. The first part is a detailed proposal, which will give you a chance to get feedback on your ideas and approach. The second part is the final essay, describing a specific philosophical problem, and explaining how we can use ideas from probability and decision theory to investigate it. See the [class schedule] (#schedule) for deadlines.
I will distribute separate handouts describing this project in more detail.
There will be one in-class midterm (see the class schedule).
To help you consolidate your understanding
To evaluate your knowledge and understanding of the main ideas
To evaluate your ability to apply core skills
There will be a comprehensive in-class final exam.
To give you an opportunity to reflect on what you have learned through the whole semester, and put all the pieces together.
To evaluate your understanding of ideas and mastery of skills from the entire class, and your ability to apply them.
Life is messy, and sometimes you just can’t reasonably get homework done on time. Instead of dealing with all of these problems case by case, everyone gets ten “late days” to use on any problem set or either part of the modeling project, no questions asked.
You can split up your late days however you want: for example, you can spend all your late days on one assignment and turn it in ten days late, or you can turn in every assignment one day late. (You can’t use just half a late day, though: if the assignment is a few hours late, that uses up a whole late day. Days when we don’t have class meetings still count, including weekends and holidays.)
There is no grade penalty for spending a late day. But after you have spent all of your late days, you will not get any more credit for late work. So don’t spend all your late days on the first assignment! Save them for real emergencies when you need them.
Late work can be turned into Jeff’s mailbox in the main philosophy office (MHP 113). Make sure to write the date and time that you turn it in at the top.
Reading questions, check-in quizzes, and discussion activities cannot be made up or turned in late. This is because these assignments are difficult to fairly administer at alternative times, and each particular one of them is worth a very small fraction of your overall grade.
So I guess this pandemic thing is still happening. We will follow all Los Angeles and USC rules. At least for now, this means masks whenever we’re inside. (N95s work best!) We are also planning to hold office hours outside or on Zoom.
Please do not come to class if you have symptoms or have been exposed to COVID. Send me an email, and we’ll work it out.
Nobody knows what’s coming next. We may have to switch to online, in which case we will take that as it comes. If you need special accommodations, let me know right away and we’ll see what we can do.
Be safe out there!
The following schedule is provisional. I will make adjustments through the semester. Watch for updates.
RB is Reason Better (available through Top Hat). O&E is Odds and Ends (available free online). Other readings besides these will also be distributed through Top Hat.
| Date | Topic | Read This | Turn This In |
|---|---|---|---|
| Part 1 | Thinking Clearly | ||
| M Aug 23 | The true and the good. | RB ch. 1, “Reasoning” | |
| W Aug 25 | Thinking fast and slow. Your mind’s two systems, and why they matter | RB ch. 1, “Reasoning” | |
| M Aug 30 | Mindset. Accuracy, degrees of confidence, bias | RB sec. 2.1 and 2.2 “Mindset” | |
| Part 2 | Responding to Evidence | ||
| W Sep 1 | Evidence. The evidence test. | RB sec. 2.3 and 5.1 | |
| M Sep 6 | Labor Day | ||
| W Sep 8 | How to change your mind. Strength factors, odds, updating | RB sec. 8.1 “Updating” | |
| M Sep 13 | Ifs, ands, ors. Conjunctions and disjunctions | RB sec. 8.2 “Updating”. Optional: O&E ch 5 “Calculating Probabilities” | |
| W Sep 15 | What if? Calculating conditional probabilities | O&E ch. 6 “Conditional Probability” | Problem set 1: evidence |
| M Sep 20 | Calculating probabilities | O&E ch. 7 “Calculating Probabilities, Part 2” | |
| W Sep 22 | Looking at the whole picture. Selection effects, media biases | RB sec. 5.2, 5.3 “Evidence” | |
| M Sep 27 | Class canceled | ||
| W Sep 29 | How to outsmart doctors, lawyers, and the police. Updating pitfalls, prior neglect | RB sec. 8.3 and 8.4 “Updating”. Optional: Jemisin, “Non-Zero Probabilities” | Problem set 2: calculating probabilities |
| M Oct 4 | Do you believe in miracles? A probability application. Midterm review | Hume, “Of Miracles” | |
| W Oct 6 | Midterm | Midterm (in class) | |
| Part 3 | Choosing Well | ||
| M Oct 11 | Consider your options. Decision tables and decision trees | RB sec. 9.1 “Decisions” | |
| W Oct 13 | Tell me what you want (what you really really want). Utility and expected utility | O&E ch. 12 “Utility” | |
| M Oct 18 | Mistakes were made. Decision-making pitfalls | RB sec. 9.2 “Decisions” | |
| W Oct 20 | Is voting pointless? A decision theory application | Barnett, “Why You Should Vote to Change the Outcome”, sections 1–4 | Problem Set 3: expected utility |
| M Oct 25 | Long shots. Extreme decision theory. | Bostrom, “Pascal’s Mugging”. Optional: Bostrom, “Astronomical Waste” | |
| Part 4 | Philosophical Foundations | ||
| W Oct 27 | Why should I? Long run arguments, axiomatic arguments | Decision Theory FAQ, secs. 8–8.6.2 | Modeling Project Part 1 |
| M Nov 1 | Risk and rationality The independence axiom, the Allais paradox | O&E sec. 13.1–13.3, “Challenges to Expected Utility” | |
| W Nov 3 | Belief and action. Betting rates | O&E ch. 16 (“Beliefs and Betting Rates” | |
| M Nov 8 | Coherence. Dutch books | O&E ch. 17 (“Dutch Books”) | |
| W Nov 10 | Close to the truth. Accuracy | Pettigrew, selections from Accuracy and the Laws of Credence | Problem set 4: philosophical foundations |
| Part 5 | Working Together | ||
| M Nov 15 | Sudden but inevitable betrayal. Game theory basics, prisoner’s dilemmas | Peterson, sec. 11.1–11.3 | |
| W Nov 17 | Coordination and trust. Nash equilibrium strategies, stag hunts | Peterson, sec. 11.5, 12.1 | Modeling Project Part 2 |
| M Nov 22 | Game theory applications. | ||
| W Nov 24 | Thanksgiving break | ||
| M Nov 29 | Game theory applications. | ||
| W Dec 1 | Catch-up and review | Problem set 5: game theory | |
| F Dec 10 | Final exam | Final exam 2–4pm |
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