Open main menu
The Logic Portal
a portal for Wikipedia's Logic resources.
Article · Category · List · Outline · WikiProject


Logic (from the Ancient Greek: λογική, translit. logikḗ), is the systematic study of the form of valid inference, and the most general laws of truth. A valid inference is one where there is a specific relation of logical support between the assumptions of the inference and its conclusion. In ordinary discourse, inferences may be signified by words such as therefore, hence, ergo, and so on.

There is no universal agreement as to the exact scope and subject matter of logic (see § Rival conceptions, below), but it has traditionally included the classification of arguments, the systematic exposition of the 'logical form' common to all valid arguments, the study of proof and inference, including paradoxes and fallacies, and the study of syntax and semantics. Historically, logic has been studied in philosophy (since ancient times) and mathematics (since the mid-19th century), and recently logic has been studied in computer science, linguistics, psychology, and other fields.

Selected article

This diagram shows the syntactic entities which may be constructed from formal languages. The symbols and strings of symbols may be broadly divided into nonsense and well-formed formulas. A formal language can be thought of as identical to the set of its well-formed formulas. The set of well-formed formulas may be broadly divided into theorems and non-theorems. However, quite often, a formal system will simply define all of its well-formed formula as theorems.[1]
In the formal languages used in mathematical logic and computer science, a well-formed formula or simply formula[2] (often abbreviated wff, pronounced "wiff" or "wuff") is an idea, abstraction or concept which is expressed using the symbols and formation rules (also called the formal grammar) of a particular formal language. To say that a string of symbols is a wff with respect to a given formal grammar is equivalent to saying that belongs to the language generated by . A formal language can be identified with the set of its wffs.

Selected biography

Bertrand Russell transparent bg.png
Bertrand Arthur William Russell, 3rd Earl Russell OM FRS (18 May 1872 – 2 February 1970), was a British philosopher, logician, mathematician and advocate for social reform.

A prolific writer, he was also a populariser of philosophy and a commentator on a large variety of topics, ranging from very serious issues to those much less so. Continuing a family tradition in political affairs, he was a prominent anti-war activist, championing free trade between nations and anti-imperialism.


Related portals


Things to do

Here are some tasks awaiting attention:


  1. ^ Godel, Escher, Bach: An Eternal Golden Braid, Douglas Hofstadter
  2. ^ Because non-well-formed formulas are rarely considered, some authors ignore them altogether. For these authors, "formula" and "well-formed formula" are synonyms. Other authors use the term "formula" for any string of symbols in the language; certain of these strings are then singled out as the well-formed formulas.


The following Wikimedia Foundation sister projects provide more on this subject:






Learning resources

Travel guides



Purge server cache