PHI 201: Introductory Logic

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Logic is the oldest and most foundational of the university disciplines — having been taught every year for at least a thousand years. The goal is to equip you with most general possible framework for sound and rigorous reasoning — one that will support you in any intellectual activity you pursue (e.g. mathematics, politics, chemistry, English literature, law, religion, etc.). What’s more, logic aspires to be independent of the quirks of a particular natural language, programming language, or mathematical system. In this sense, logic aims to to capture that which is universally rational. (We might argue later about the extent to which logic is universal, but we will have to use logic to do that!)

Instructors

• Quanzhi: Wednesday 10:40-12:00, 1:20-2:40
• Ludovica: Wednesday 1:20-2:40, 2:55-4:15
• Pacy: Wednesday 9:00-10:20, 10:40-12:00
• Chris: Wednesday 9:00-10:20, 10:40-12:00
• Junyan: Wednesday 9:00-10:20, 10:40-12:00
• Jake: Wednesday 9:00-10:20, 10:40-12:00
• Jaehyun: Wednesday 9:00-10:20 and Thursday 1:20-2:40
• Hans: Wednesday 1:20-2:40

Course format

• One 80 minute lecture, and one 80 minute “workshop” (i.e. precept) each week
• Problem sets approximately every week (50% of grade). Drafts of all psets are linked to this page. However, the official pset is not released until seven days before the due date. One pset may be dropped.
• In class midterm exam (15% of grade)
• In class final exam (30% of grade)
• Engagement and participation (5% of grade)

Late policy

We are unable to accept late homework, except in case of a documented medical or family emergency.

Recommended work protocol

1. Weekend before lecture
   1. Look over next problem set
   2. Skim relevant section of text
2. Monday: Attend lecture and take notes
3. Between lecture and precept
   1. Read text more closely
   2. Work on pset
   3. Look at feedback on previous week’s pset
4. Wednesday: Attend precept
   1. Review previous week’s pset
   2. Work on this week’s pset
5. Optionally: visit preceptor’s office hours
6. Friday: submit pset

Academic integrity

The policy for this course is that collaboration between students is encouraged, but in no case should one student copy another’s work. That is hardly a precise criterion, but the spirit of the law is that you need to understand what you write down on your paper. If you fail to do that, then your lack of understanding will most likely reveal itself on the exam. As a general rule, we would suggest that you put away any notes from joint brainstorming sessions before writing your final answers.

It would be pointless for us to try to prevent you from using ChatGPT and the like. But please note: we have tested ChatGPT on the problem sets for this class, and in our experience, it is not reliable in giving correct solutions. It gave us, e.g., a “proof” of Pierce’s law that did not use the DN rule (which is provably impossible).

Resources

• The text How Logic Works can be accessed via Princeton library subscription at jstor. However, please consider purchasing a hardback copy from Princeton University Press, Labyrinth, or another bookseller.
• Proof checker: https://lemmon-checker.fly.dev
  
• Solutions to selected problems in the textbook
• The LaTeX source files for the textbook can be accessed here: hhalvors/logic-works

Subject matter

While this subject has been taught for over a millenium, the content got an overhaul in the mid 1900s, when modern symbolic logic was consolidated. (The content has been stable since the 1950s.) Since then, the standard format for an introductory logic class has been to learn the “predicate calculus” in three steps: propositional logic, monadic predicate logic, polyadic predicate logic. We follow this same outline, but with a few twists.

1. We emphasize reasoning techniques (natural deduction) over calculational techniques (truth tables or trees).
2. We teach proofs before truth tables. It’s harder, but makes your brain stronger.
3. We incorporate more analysis of arguments in natural language (e.g. argument mapping).
4. We illustrate logical concepts, when helpful, by displaying them concretely in the general framework of functional programming languages. However, this course presupposes no background in programming, nor does it presuppose that students are interested in programming.

Schedule

Week 1