Introduction to Logic


Welcome to the Learn Logic course in the Learn section of In this course, we will learn about argumentation, propositional logic, predicate logic, and modal logic.


A mature understanding of English is required for this course. Otherwise, there are no prerequisites.

What is Logic?

Logic is the systematic study of logical consequence and the relationships between meanings.

Why study Logic?

It is sometimes difficult to determine whether reasoning is correct or incorrect. Logic is used to help deconstruct reasoning to reveal inconsistencies and misleading conclusions.

Logic is used to some extent in all academic fields, but it is best known to be used in philosophy and mathematics.

By learning logic and using it in your everyday life, you can make better sense of information on the internet and analyze the reasoning used by your friends and family. Excessive use of logic may lead to sour relationships, but a healthy use of it can lead to a more logically consistent lifestyle.

What is an argument?

An argument is a set of sentences that claim some state of affairs. An argument have other arguments within them, known as subarguments, or can be part of other arguments, known as superarguments.

Types of Sentences

Traditionally, the sentences in arguments were restricted to declarative or indicative sentences, which claim some state of affairs and are either true or false. Introductory logic is usually confined to these sentences, but we can also study the logic vague sentences, those that are not strictly true or false. This is known as fuzzy logic.

Logical Validity

An argument is considered valid or logically valid if it can be divided into two subsets known as the premises and the conclusion such that if all the sentences in the premises are true, then the sentences in the conclusion must also be true.

Typically, the first few sentences in an argument are known as premises and the final resulting claim in an argument is known as the conclusion, but the order of the sentences does not affect logical validity.

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