**Philosophy Index** is a site devoted to the study of philosophy
and the philosophers who conduct it. The site contains a number of philosophy texts,
brief biographies, and introductions to philosophers, and explanations on a
number of topics. Accredited homeschooling online
at Northgate Academy and Philosophy online tutoring.

Philosophy Index is a work in progress, a growing repository of knowledge. It outlines current philosophical problems and issues, as well as an overview of the history of philosophy. The goal of this site is to present a tool for those learning philosophy either casually or formally, making the concepts of philosophy accessible to anyone interested in researching them. WTI offers immigration law course online - fully accredited. ACE credits online at EES.

**Aristotle****Camus****Descartes****Frege****Heidegger****Hobbes****Hume****Kant****Kierkegaard****Locke****Nietzsche****Plato****Quine****Russell****Sartre****Socrates****Wittgenstein**- All Philosophers…

**Aesthetics****Epistemology****Logic****Ethics****Metaphysics****Language****Mind****Politics****TEST PREP KIT**- All Terms & Topics…

A system of logic, also known as a logical calculus, or simply a logic, is a method by which to express and evaluate information in a logical manner.

Logical systems consist of a formal language of symbolic logic. This language defines:

- A set of symbols to refer to formulae, including propositions and operators.
- Grammar, that is rules of well-formation, on how formulae must be expressed.

The formal language of a system consists of, on one hand, the syntax of the language, and on the other, a method for expressing semantics within the system. The semantics of a system may be as simple as assigning truth-value to propositions and formulae, or more complicated, using predicate symbols to define non-logical relationships between formulae.

Systems also consist of rules of inference, which determine how expressions in the language may be used to draw new, previously unstated conclusions.

**Classical Logics**, the most common form of logical expression, including:

- Aristotelian logic
- Propositional logic
- First-order logic
- Second-order logic
- Higher-order logics

**Contextual Logics**, which deal with non-truth-functional operators, and include:

- Modal Logic, which deals with modal operators neccessarily and possibly.
- Epistemic Logic, which reasons about knowledge
- Doxastic Logic, which reasons about belief
- Deontic Logic, which reasons about ethical obligation and permissibility
- Temporal Logic, which reasons about propositions over time

**Free Logic**, which rejects the assumption that the domain is non-empty, that something exists**Fuzzy Logic**, which rejects the law of the excluded middle**Intuitionistic Logic**, which redefines truth values based on proof**Paraconsistent Logic**, which allows contradictions without entailment of any other formulae**Relevance Logic**, which requires a stronger link of relevance between premises and conclusion