Philosophical logic
Philosophical logic is a term introduced by Bertrand Russell
Bertrand Russell
Bertrand Arthur William Russell, 3rd Earl Russell, OM, FRS was a British philosopher, logician, mathematician, historian, and social critic. At various points in his life he considered himself a liberal, a socialist, and a pacifist, but he also admitted that he had never been any of these things...

 to represent his idea that the workings of natural language
Natural language
In the philosophy of language, a natural language is any language which arises in an unpremeditated fashion as the result of the innate facility for language possessed by the human intellect. A natural language is typically used for communication, and may be spoken, signed, or written...

 and thought
"Thought" generally refers to any mental or intellectual activity involving an individual's subjective consciousness. It can refer either to the act of thinking or the resulting ideas or arrangements of ideas. Similar concepts include cognition, sentience, consciousness, and imagination...

 can only be adequately represented by an artificial language; essentially it was his formalization program for the natural language. Today the term is used with several different meanings.

One modern meaning, espoused mainly by philosophers, is that philosophical logic is the study of the more specifically philosophical aspects of logic in contrast with symbolic logic; for example Sybil Wolfram lists the study of the concepts of argument
In philosophy and logic, an argument is an attempt to persuade someone of something, or give evidence or reasons for accepting a particular conclusion.Argument may also refer to:-Mathematics and computer science:...

, meaning, and truth
Truth has a variety of meanings, such as the state of being in accord with fact or reality. It can also mean having fidelity to an original or to a standard or ideal. In a common usage, it also means constancy or sincerity in action or character...

. Colin McGinn
Colin McGinn
Colin McGinn is a British philosopher currently working at the University of Miami. McGinn has also held major teaching positions at Oxford University and Rutgers University. He is best known for his work in the philosophy of mind, though he has written on topics across the breadth of modern...

 includes identity
-Philosophical topics:* Identity , also called sameness, is whatever makes an entity definable and recognizable* Law of identity, principle of logic stating that an object is the same as itself...

, existence
In common usage, existence is the world we are aware of through our senses, and that persists independently without them. In academic philosophy the word has a more specialized meaning, being contrasted with essence, which specifies different forms of existence as well as different identity...

, predication, necessity
In U.S. criminal law, necessity may be either a possible justification or an exculpation for breaking the law. Defendants seeking to rely on this defense argue that they should not be held liable for their actions as a crime because their conduct was necessary to prevent some greater harm and when...

, and truth
Truth has a variety of meanings, such as the state of being in accord with fact or reality. It can also mean having fidelity to an original or to a standard or ideal. In a common usage, it also means constancy or sincerity in action or character...

 as the main topics of his book, which he writes was that was aimed "to bring philosophy back into philosophical logic". John Woods
John Woods (logician)
John Hayden Woods is a Canadian logician and philosopher, currently Director of the Abductive Systems Group at the University of British Columbia and The UBC Honorary Professor of Logic. He has also been affiliated with the Group on Logic, Information and Computation, of the Department of...

 writes that philosophical logic investigates properties such as truth, meaning and reference
Reference is derived from Middle English referren, from Middle French rèférer, from Latin referre, "to carry back", formed from the prefix re- and ferre, "to bear"...

 in natural languages. As contrasting example he argues that Frege's Begriffsschrift
Begriffsschrift is a book on logic by Gottlob Frege, published in 1879, and the formal system set out in that book...

is an example of mathematical logic
Mathematical logic
Mathematical logic is a subfield of mathematics with close connections to foundations of mathematics, theoretical computer science and philosophical logic. The field includes both the mathematical study of logic and the applications of formal logic to other areas of mathematics...

, while Frege's discussion of sense and reference
Sense and reference
Sinn and bedeutung are usually translated, respectively, as sense and reference. Two different aspects of some terms' meanings, a term's reference is the object that the term refers to, while the term's sense is the way that the term refers to that object.Sinn and bedeutung were introduced by...

 belongs to the philosophical logic realm. Woods also points out that there's substantial overlap between philosophy of language
Philosophy of language
Philosophy of language is the reasoned inquiry into the nature, origins, and usage of language. As a topic, the philosophy of language for analytic philosophers is concerned with four central problems: the nature of meaning, language use, language cognition, and the relationship between language...

 and philosophical logic. Susan Haack
Susan Haack
Susan Haack is an English professor of philosophy and law at the University of Miami in the United States. She has written on logic, the philosophy of language, epistemology, and metaphysics. Her pragmatism follows that of Charles Sanders Peirce.-Career:Haack is a graduate of the University of...

 argued that there is no distinction between philosophical logic seen this way and philosophy of logic
Philosophy of logic
Following the developments in Formal logic with symbolic logic in the late nineteenth century and mathematical logic in the twentieth, topics traditionally treated by logic not being part of formal logic have tended to be termed either philosophy of logic or philosophical logic if no longer simply...

. A. C. Grayling
A. C. Grayling
Anthony Clifford Grayling is a British philosopher. In 2011 he founded and became the first Master of New College of the Humanities, a private undergraduate college in London. Until June 2011, he was Professor of Philosophy at Birkbeck, University of London, where he taught from 1991...

 disagrees however, writing that when "one does philosophy of logic, one is philosophizing about logic; but when one does philosophical logic one is philosophizing." He concedes however that the distinction is not too sharp. In general there is no agreement whether these two fields coincide or not.

Another meaning assigned to philosophical logic today is that it addresses mainly extensions and alternatives to classical logic
Classical logic
Classical logic identifies a class of formal logics that have been most intensively studied and most widely used. The class is sometimes called standard logic as well...

, the so called non-classical logic
Non-classical logic
Non-classical logics is the name given to formal systems which differ in a significant way from standard logical systems such as propositional and predicate logic. There are several ways in which this is done, including by way of extensions, deviations, and variations...

s. In this sense, philosophical logic is a technical subject. Texts such as John P. Burgess
John P. Burgess
John Burgess is a John N. Woodhull Professor of Philosophy at Princeton University. He received his Ph.D. from UC Berkeley's Group in Logic and Methodology of Science. His interests include logic, philosophy of mathematics and metaethics...

' Philosophical Logic, the Blackwell Companion to Philosophical Logic, or the multi-volume Handbook of Philosophical Logic(edited by Dov M. Gabbay and Franz Guenthner
Franz Guenthner
Franz Guenthner is a professor of Computational Linguistics at the Center for Information and Language Processing at the Ludwig-Maximilians-Universitaet in Munich, Germany...

) address this latter meaning of the term, with classical logic included as a core component however. According to Burgess, philosophical logic in this sense, has its center of gravity in theoretical computer science
Theoretical computer science
Theoretical computer science is a division or subset of general computer science and mathematics which focuses on more abstract or mathematical aspects of computing....

, because many non-classical logics find applications there. The Springer Journal of Philosophical Logic
Journal of Philosophical Logic
The Journal of Philosophical Logic, is a peer-reviewed scientific journal founded in 1972. It is published by Springer and "provides a forum for work at the crossroads of philosophy and logic, old and new, with contributions ranging from conceptual to technical.Accordingly, the Journal publishes...

largely addresses this conception of philosophical logic.

Yet another contemporary meaning proposed by Dale Jacquette is that philosophical logic is philosophy in which any recognized methods of logic are used to solve or advance the discussion of philosophical problems.
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