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== Informal Logic ==

== Informal Logic ==

The art of [[rhetoric]] is sometimes called "informal logic", and the classic [[logical fallacies|fallacies]] are often described as "logical fallacies", though, strictly speaking, most of them are simply emotionally effective ways to build an invalid argument.  Generally speaking, "informal logic" consists of "common sense" and a collection of other rather loose rules that people employ while making most decisions and even in debate. It is unstructured, and depends largely on one's view of "the reasonable". The thresholds of what is "reasonable" and what is not, are inexact and subject to change with the receipt of sufficient contrary evidence--and again, what constitutes "sufficiency" in this context might vary from person to person.  

The art of [[rhetoric]] is sometimes called "informal logic", and the classic [[logical fallacies|fallacies]] are often described as "logical fallacies", though, strictly speaking, most of them are simply emotionally effective ways to build an invalid argument.  Generally speaking, "informal logic" consists of "common sense" and a collection of other rather loose rules that people employ while making most decisions and even in debate. It is unstructured, and depends largely on one's view of "the reasonable". The thresholds of what is "reasonable" and what is not, are inexact and subject to change with the receipt of sufficient contrary evidence—and again, what constitutes "sufficiency" in this context might vary from person to person.  

== Deduction and Induction ==

== Deduction and Induction ==

Logic is also used extensively in [[theology]], and especially the study of the [[Bible]], which, due to its divine inspiration, is very logical.  

Logic is also used extensively in [[theology]], and especially the study of the [[Bible]], which, due to its divine inspiration, is very logical.  

Logic, and especially formal logic, inform the discipline of [[critical thinking]]--which, by no coincidence, takes its name from the Greek word for a judge. Indeed, judges and juries in courts of [[law]] must apply logic, both formal and informal, to arrive at their decisions. Formal logic will usually serve to state what obedience to a given body of law requires; informal logic must usually serve a trier of fact charged with deciding whether a given person was in obedience or in violation. The latter principle holds primarily because plaintiff and defendant in a court of law quite often ''do not'' agree on matters of fact.

Logic, and especially formal logic, inform the discipline of [[critical thinking]]—which, by no coincidence, takes its name from the Greek word for a judge. Indeed, judges and juries in courts of [[law]] must apply logic, both formal and informal, to arrive at their decisions. Formal logic will usually serve to state what obedience to a given body of law requires; informal logic must usually serve a trier of fact charged with deciding whether a given person was in obedience or in violation. The latter principle holds primarily because plaintiff and defendant in a court of law quite often ''do not'' agree on matters of fact.

== Propositional calculus ==

== Propositional calculus ==

Propositional calculus is the study of [[logic]]al propositions, that is, logical statements that might or might not be true under various interpretations. A good deal of the study concerns how to prove theorems in symbolic logic.

Propositional calculus is the study of logical propositions, that is, logical statements that might or might not be true under various interpretations. A good deal of the study concerns how to prove theorems in symbolic logic.

[[Lewis Carroll]] wrote a book on it for young students.

[[Lewis Carroll]] wrote a book on it for young students.

* Geoffrey Hunter, "Metalogic"

* Geoffrey Hunter, "Metalogic"

== See Also ==

== See also ==

*[[Atheism and logic]]

*[[Atheism and logic]]

[[Category:Philosophy]]

[[Category:Philosophy]]