Propositions, compound statements and truth values
Description of the concept...
Learn about it
The following is a series of slides and videos that will help you understand, learn about and review this sub-topic.
Keep track of your progress, look at the revision cards and practice the exam questions on this Logic document
Use these slides to review the material and key points covered in the videos.
This is an introduction to the idea of symbolic logic, the language, the notation and the idea of compound logical statements.
Language, words and symbols
How do we take compound statements written in words and write them in symbols? What about the other way around? This video answers the questions.
Standard results - AND, OR, NEGATION
The formula booklet has a set of standard results for AND, OR and NEGATION. Here we explain those and get to the point that we know these off by heart because they make sense!
Standard Results - Implication
Implication has caused many a headache over the years and it is an excellent thought exercise to discuss it. This video explains how following the 'TRUE until proven FALSE' approach can bypass the headache! The first video covers straight implication, the second looks at If and only IF.
Constructing truth tables - 2 and 3 propositions
In these two videos we go over constructing and completing truth tables involving both 2 and 3 propositions. One column at a time, one row at a time, we are only ever comparing 2 truth values to deduce a third.
Contradiction, Tautology and Validity
What if all the truth values are 'False'? What if they are 'True'? These videos cover these important ideas with some examples leading up to the notion of a 'Valid Argument'
What does it mean when to compound logical statements are said to be logically equivalent? Here is an explanation with a couple of examples to show the point.
Converse, Inverse and Contrapositive
These definitions are not given in your formula booklets and you need to have them committed to memory. This video explains what they are and what they mean.
This section of the page can be used for quick review. The flashcards help you go over key points and the quiz lets you practice answering questions on this subtopic.
Review these condensed 'key point' Revision cards to help you check and keep ideas fresh in your mind.
Practice your understanding on these quiz questions. Check your answers when you are done and read the hints where you got stuck. If you find there are still some gaps in your understanding then go back to the videos and slides above.
Exam Style Questions
The following questions are based on IB exam style questions from past exams. You should print these off (from the document at the top) and try to do these questions under exam conditions. Then you can check your work with the video solution.
First question and video
Second question and video solution
Third question and video solution