Life, the Universe, and Everything

A Course Blog for GET1029/GEK1067

Category: Logic

Omnipotence and Explosion

Click on image to see Kitty’s reaction upon discovering the Principle of Explosion…

I said a bit about how the idea that God–an omnipotent being–can do the logically impossible is probably not a good idea to accept, whether you are an Atheist attempting to push the Logical Problem of Evil (“Why, your God can’t do that? Not all powerful izzit?”), or a Theist trying to defuse the Logical Problem of Evil. This post expands on that idea and introduces you to a point about logic called the Principle of Explosion.

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Contradiction and Inconsistency (or, the problem with the Logical Problem of Evil)

This is an expansion on the last segment of W08 and the stuff from earlier in the lecture that leads up to it. Since it concerns what many philosophers of religion now perceive to be the critical weakness of the LPOE–prompting them to move to an inductive/evidential rather than a strictly logical formulation of the Problem–it bears a bit of re-emphasizing. (Warning: this is a longish post. I originally wrote it to help students from a previous year who said that they found the material hard to follow. This might not apply to you in this semester. But since I wrote it, might as well.)

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Answers to the two Logical Exercises in W08

Click through to see…

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A Weird Point About Logic

More bonus, optional material. The question is this–What happens when you have an “unnecessary” premise in a deductive argument? The answer is–for deductively valid arguments–nothing!

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A Couple of Points about Logic

Making explicit things that are already implied by “A Short Lesson on Arguments and Logic”; totally optional. Click through to see…

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Argument by Moral Analogy

Some of you have noticed how Norcross’ Puppy Argument, Singer’s Drowning Child Argument, and what I called Huemer’s “Sam” Argument share the same overall argumentative strategy. This a post about that overall strategy.

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Arguments Lesson Bot on Telegram

Over the last few years, my tutors and I have created a set of handouts (they are in Luminus > Module Overview > 1) to help students with basic concepts to do with arguments and logic. While formal logic (or for that matter, the formal study of informal logic) isn’t part of the syllabus of GET1029, we do introduce and reinforce concepts such as the basic idea of an argument, the difference between validity and soundness, and very importantly, necessary vs. a sufficient conditions–throughout the semester. The tutors have their marching orders to help me with all this, and the quiz questions do assume your familiarity with them. But no worries–even as you are still finding your footing in these concepts, the handouts are there to help you as ready reference material. This semester, we found a way to do something better (we hope it’s better anyway).

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LogiProof: Software for Logic Assessment (a guest post by Dr Lee Wang Yen)

(Note from the blog owner: The following is the account by Dr. Lee Wang Yen, a colleague from the Philosophy Department, concerning how he created a computer programme for assessing logic. Since 2016, Dr. Lee has been teaching GET1028 Logic and GET1026 Effective Reasoning for the Department of Philosophy. As both modules are relatively large (200-300 students each semester), we are always looking for ways to streamline or automate processes. This is not just about saving human work; more importantly, it is also about cutting down on human errors and ensuring that our teaching is scalable across larger groups of students without compromising on quality. Knowing a little about what he went through to make his logic assessment program happen, I encouraged him to do a write up for sharing and offered him a platform for hosting it. You can find out more about Dr Lee’s research at and contact him at

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1. Problem

When I first taught GET1028 Logic at NUS, I set a mixture of Multiple Choice Questions (MCQs) and short-answer questions (SAQs). My detailed marking method (deducting 0.1, 0.2, 0.25, etc. marks depending on the seriousness of the mistakes) entailed a huge workload not only for myself, but also for the admin staff in my department, who had to help check the marks calculation. Given the size of my class and the small admin team in my department, everyone was under huge pressure to meet the deadline without compromising on accuracy. I had to work 10-11 hours a day for more than a week. The admin staff had to work over weekends. It occurred to me, given the prompting of the admin staff and department leadership, that I had to change my assessment method.

One option would be to set only MCQs. However, after many long and detailed discussions with Prof. Loy, my deputy head of department (a keen user of MCQs in the large exposure module) in 2017, we came to the conclusion that not all logic skills could be tested by MCQs. While MCQs can test a student’s ability to evaluate a proof, it cannot test a student’s ability to conduct the proof from beginning to the end. As a result, I took up my then teaching assistant’s suggestion and began to write a computer programme that eventually evolved into LogiProof. Continue reading

Necessary and Sufficient Condition

From previous experience, the ideas of a necessary condition, vs. a sufficient condition, and a necessary and sufficient condition are often not easily grasped by students. The handout in IVLE Files (“Everything you always wanted to know about arguments”) covers the relevant topics and your tutors will also be reinforcing the ideas. Below is a refresher.

For our purposes, take note of the following equivalences (everything in the same column are logically equivalent to each other):

P is a necessary condition for Q P is a sufficient condition for Q P is a necessary and sufficient condition for Q
P is necessary for Q P is sufficient for Q P is necessary and sufficient for Q
Q only if P Q if P P if and only if Q
Only if P, then Q If P then Q Q if and only if P
If Q then P P only if Q
If not P then not Q If not Q then not P

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