Logic Comes From the Greek Word for Word
Logic is reasoning conducted by strict principles. The Greek logos meant word, speech and reason all at once.
Logic is reasoning conducted according to strict principles of validity. Greek *logos* covered word, speech, account and reason together, and that single word is behind an enormous share of English vocabulary: every *-logy* is a study, from *biology* to *geology*, and *dialogue*, *analogy*, *prologue* and *logo* all descend from it. Formal logic is about the *form* of an argument: a valid argument can have false premises, and a true conclusion can follow from an invalid one.
- Reasoning by principles. *Formal logic.*
- A system of reasoning. *The logic of the argument.*
- Logical — following reason. *A logical step.*
- -logy — the study of. *Biology.*
- Greek — *logos*, word or reason. *The source.*
Word forms
| Form | Word | Example |
|---|---|---|
| Noun | logic | Cold logic. |
| Adjective | logical | A logical answer. |
| Adverb | logically | Logically speaking. |
| Agent | logician | A logician. |
| Greek | logos | Word, reason. |
- The argument fails on basic logic.Reasoning.
- Every -logy means a study.Suffix.
- A valid argument can have false premises.Formal logic.
Valid and sound
- Valid — the conclusion follows from the premises
- Sound — valid and the premises are also true
- A valid argument can reach a false conclusion from false premises
- An invalid argument can still reach a true conclusion by luck
- Only soundness guarantees a true conclusion
Greek *logike*, of reasoning, from *logos*, word, speech or reason, from *legein*, to speak.
What is the difference between valid and sound?
A valid argument has a conclusion that follows from its premises. A sound argument is valid and its premises are also true.
Why do sciences end in -logy?
From Greek logos, meaning word or account. A -logy is an account or study of something.