Study of reasoning
What Is Logic?
Logic is the systematic study of valid inference—what follows from what, and why some arguments succeed while others only persuade.
Short answer
It ranges from formal systems (propositional and predicate logic) to informal fallacies and the logic of scientific confirmation. Logic trains precision without replacing judgment about premises.
Validity and soundness
An argument is valid when the conclusion must be true if the premises are. It is sound when valid and its premises are true. Confusing rhetorical force with validity is a common error.
Formal and informal logic
Formal logic uses symbolic languages to track structure. Informal logic analyzes everyday arguments, definitions, and fallacies. Both serve philosophical writing and public debate.
Logic in the history of philosophy
Aristotle’s syllogistic, Stoic propositional insights, Indian and Chinese debates on language and standards, medieval scholastic logic, and modern mathematical logic all belong to this story.
Frequently asked questions
What is logic in philosophy?
It is the study of correct reasoning and the structure of arguments.
Do I need symbolic logic to study philosophy?
It helps for some fields, but clear informal reasoning is foundational everywhere.
How does logic relate to AI?
Classical AI used formal logic extensively; modern machine learning raises new questions about inference, explanation, and reliability.
From the archive
Read alongside this guide
“It is through wonder that people both now begin and first began to philosophize.”
“The human good is activity of soul in accordance with virtue.”
“Virtues arise in us neither by nature nor contrary to nature; we are fitted by nature to receive them, and are brought to completion by habit.”