'Logic' (from
Classical Greek λόγος
logos; meaning word, thought, idea, argument, account, reason, or principle) is the study of the principles and criteria of valid
inference and
demonstration.
As a
formal science, logic investigates and classifies the structure of statements and arguments, both through the study of
formal systems of
inference and through the study of arguments in natural language. The field of logic ranges from core topics such as the study of
fallacies and
paradoxes, to specialized analysis of reasoning using
probability and to arguments involving
causality. Logic is also commonly used today in
argumentation theory.
[1]
Traditionally, logic is studied as a branch of
philosophy, one part of the classical
trivium, which consisted of
grammar, logic, and
rhetoric. Since the mid-nineteenth century ''formal logic'' has been studied in the context of
foundations of mathematics, where it was often called
symbolic logic. In 1903
Alfred North Whitehead and
Bertrand Russell attempted to establish logic formally as the cornerstone of mathematics with the publication of
Principia Mathematica.
[2] However, the system of Principia is no longer much used, having been largely supplanted by
set theory. As the study of formal logic expanded, research no longer focused solely on foundational issues, and the study of several resulting areas of mathematics came to be called
mathematical logic. The development of formal logic and its implementation in computing machinery is the foundation of
computer science.
Nature of logic
Form is central to logic. It complicates exposition that 'formal' in "formal logic" is commonly used in an ambiguous manner. Symbolic language is just one kind of formal logic, and is distinguished from another kind of formal logic, traditional
Aristotelian syllogistic logic, which deals solely with
categorical propositions.
★ '
Informal logic' is the study of
natural language arguments. The study of
fallacies is an especially important branch of informal logic. The dialogues of
Plato [3] are a major example of informal logic.
★ 'Formal logic' is the study of
inference with purely formal content, where that content is made explicit. (An inference possesses a 'purely formal content' if it can be expressed as a particular application of a wholly abstract rule, that is, a rule that is not about any particular thing or property. The first rules of formal logic that have come down to us were written by
Aristotle.
[4] We will see later that in many definitions of logic, logical inference and inference with purely formal content are the same. This does not render the notion of informal logic vacuous, because no formal language captures all of the nuance of natural language.)
★ '
Symbolic logic' is the study of symbolic abstractions that capture the formal features of logical inference.
Symbolic logic is often divided into two branches,
propositional logic and
predicate logic.
★ '
Mathematical logic' is an extension of symbolic logic into other areas, in particular to the study of
model theory,
proof theory,
set theory, and
recursion theory.
"Formal logic" is often used as a synonym for symbolic logic, where informal logic is then understood to mean any logical investigation that does not involve symbolic abstraction; it is this sense of 'formal' that is parallel to the received usages coming from "
formal languages" or "
formal theory". In the broader sense, however, formal logic is old, dating back more than two millennia, while symbolic logic is comparatively new, only about a century old.
Consistency, soundness, and completeness
Among the valuable properties that formal systems can have are:
:
★ '
Consistency', which means that none of the theorems of the system contradict one another.
:
★ '
Soundness', which means that the system's rules of proof will never allow a false inference from a true premise. If a system is sound and its axioms are true then its theorems are also guaranteed to be true.
:
★ '
Completeness', which means that there are no true sentences in the system that cannot, at least in principle, be proved in the system.
Not all systems achieve all three virtues. The work of
Kurt Gödel has shown that no useful system of arithmetic can be both consistent and complete: see
Gödel's incompleteness theorems.
Rival conceptions of logic
Logic arose (see below) from a concern with correctness of
argumentation. The conception of logic as the study of argument is historically fundamental, and was how the founders of distinct traditions of logic, namely
Plato and
Aristotle, conceived of logic. Modern logicians usually wish to ensure that logic studies just those arguments that arise from appropriately general forms of inference; so for example the
Stanford Encyclopedia of Philosophy says of logic that it "does not, however, cover good reasoning as a whole. That is the job of the theory of rationality. Rather it deals with inferences whose validity can be traced back to the formal features of the representations that are involved in that inference, be they linguistic, mental, or other representations" (Hofweber 2004).
By contrast
Immanuel Kant introduced an alternative idea as to what logic is. He argued that logic should be conceived as the science of judgement, an idea taken up in
Gottlob Frege's logical and philosophical work, where thought (German: ''Gedanke'') is substituted for judgement (German: ''Urteil''). On this conception, the valid inferences of logic follow from the structural features of judgements or thoughts.
Deductive and inductive reasoning
Deductive reasoning concerns what follows necessarily from given premises. However,
inductive reasoning—the process of deriving a reliable generalization from observations—has sometimes been included in the study of logic. Correspondingly, we must distinguish between deductive validity and
inductive validity. An inference is deductively valid if and only if there is no possible situation in which all the premises are true and the conclusion false. The notion of deductive validity can be rigorously stated for systems of formal logic in terms of the well-understood notions of
semantics. Inductive validity on the other hand requires us to define a ''reliable generalization'' of some set of observations. The task of providing this definition may be approached in various ways, some less formal than others; some of these definitions may use
mathematical models of probability. For the most part this discussion of logic deals only with deductive logic. Deductive argument follows the pattern of a general premise to a particular one, there is a very strong relationship between the premise and the conclusion of the argument.
History of logic
Main articles: History of logic
Many cultures have employed intricate systems of reasoning and asked questions about logic or propounded logical paradoxes. For example, in
India, the
Nasadiya Sukta of the
Rigveda (
RV 10.129) contains
ontological speculation in terms of various logical divisions that were later recast formally as the four circles of ''
catuskoti'': "A", "not A", "A and not A", and "not A and not not A".
[6] and the Chinese philosopher 'Gongsun Long' (ca.
325–
250 BC) proposed the paradox "One and one cannot become two, since neither becomes two."
[7]
The first sustained work on the subject of logic which has survived was that of
Aristotle.
[8] The formally sophisticated treatment of modern logic descends from the Greek tradition, the latter mainly being informed from the transmission of
Aristotelian logic.
The traditions outside Europe did not survive into the modern era: in China, the tradition of scholarly investigation into logic was repressed by the
Qin dynasty following the legalist philosophy of
Han Feizi; in the Islamic world the rise of the
Asharite school suppressed original work on logic.
However in India, innovations in the scholastic school, called
Nyaya, continued into the early
18th century. It did not survive long into the
colonial period. In the 20th century, western philosophers like
Stanislaw Schayer and
Klaus Glashoff have tried to explore certain aspects of the
Indian tradition of logic. According to
Hermann Weyl (1929):
During the medieval period, major efforts were made to show that Aristotle's ideas were compatible with
Christian faith. During the later period of the Middle Ages, logic became a main focus of philosophers, who would engage in critical logical analyses of philosophical arguments.
Topics in logic
Throughout history, there has been interest in distinguishing good from bad arguments, and so logic has been studied in some more or less familiar form.
Aristotelian logic has principally been concerned with teaching good argument, and is still taught with that end today, while in
mathematical logic and
analytical philosophy much greater emphasis is placed on logic as an object of study in its own right, and so logic is studied at a more abstract level.
Consideration of the different types of logic explains that logic is not studied in a vacuum. While logic often seems to provide its own motivations, the subject develops most healthily when the reason for our interest is made clear.
Syllogistic logic
Main articles: Aristotelian logic
The ''
Organon'' was
Aristotle's body of work on logic, with the ''
Prior Analytics'' constituting the first explicit work in formal logic, introducing the syllogistic. The parts of syllogistic, also known by the name
term logic, were the analysis of the judgements into propositions consisting of two terms that are related by one of a fixed number of relations, and the expression of inferences by means of
syllogisms that consisted of two propositions sharing a common term as premise, and a conclusion which was a proposition involving the two unrelated terms from the premises.
Aristotle's work was regarded in classical times and from medieval times in Europe and the Middle East as the very picture of a fully worked out system. It was not alone: the
Stoics proposed a system of
propositional logic that was studied by medieval logicians; nor was the perfection of Aristotle's system undisputed; for example the
problem of multiple generality was recognised in medieval times. Nonetheless, problems with syllogistic logic were not seen as being in need of revolutionary solutions.
Today, some academics claim that Aristotle's system is generally seen as having little more than historical value (though there is some current interest in extending term logics), regarded as made obsolete by the advent of
sentential logic and the
predicate calculus. Others use Aristotle in
argumentation theory to help develop and critically question argumentation schemes that are used in
artificial intelligence and
legal arguments.
Predicate logic
Main articles: Predicate logic
Logic as it is studied today is a very different subject to that studied before, and the principal difference is the innovation of predicate logic. Whereas Aristotelian syllogistic logic specified the forms that the relevant part of the involved judgements took, predicate logic allows sentences to be analysed into subject and argument in several different ways, thus allowing predicate logic to solve the
problem of multiple generality that had perplexed medieval logicians. With predicate logic, for the first time, logicians were able to give an account of
quantifiers general enough to express all arguments occurring in natural language.
The development of predicate logic is usually attributed to
Gottlob Frege, who is also credited as one of the founders of
analytical philosophy, but the formulation of predicate logic most often used today is the
first-order logic presented in
Principles of Theoretical Logic by
David Hilbert and
Wilhelm Ackermann in
1928. The analytical generality of the predicate logic allowed the formalisation of mathematics, and drove the investigation of
set theory, allowed the development of
Alfred Tarski's approach to
model theory; it is no exaggeration to say that it is the foundation of modern
mathematical logic.
Frege's original system of predicate logic was not first-, but second-order.
Second-order logic is most prominently defended (against the criticism of
Willard Van Orman Quine and others) by
George Boolos and
Stewart Shapiro.
Modal logic
Main articles: Modal logic
In languages,
modality deals with the phenomenon that subparts of a sentence may have their semantics modified by special verbs or modal particles. For example, "''We go to the games''" can be modified to give "''We should go to the games''", and "''We can go to the games''"" and perhaps "''We will go to the games''". More abstractly, we might say that modality affects the circumstances in which we take an assertion to be satisfied.
The logical study of modality dates back to
Aristotle, who was concerned with the
alethic modalities of necessity and possibility, which he observed to be dual in the sense of
De Morgan duality. While the study of necessity and possibility remained important to philosophers, little logical innovation happened until the landmark investigations of
Clarence Irving Lewis in
1918, who formulated a family of rival axiomatisations of the alethic modalities. His work unleashed a torrent of new work on the topic, expanding the kinds of modality treated to include
deontic logic and
epistemic logic. The seminal work of
Arthur Prior applied the same formal language to treat
temporal logic and paved the way for the marriage of the two subjects.
Saul Kripke discovered (contemporaneously with rivals) his theory of
frame semantics which revolutionised the formal technology available to modal logicians and gave a new
graph-theoretic way of looking at modality that has driven many applications in
computational linguistics and
computer science, such as
dynamic logic.
Deduction and reasoning
Main articles: Deductive reasoning
The motivation for the study of logic in ancient times was clear, as we have described: it is so that we may learn to distinguish good from bad arguments, and so become more effective in argument and oratory, and perhaps also, to become a better person.
This motivation is still alive, although it no longer takes centre stage in the picture of logic; typically
dialectical logic will form the heart of a course in
critical thinking, a compulsory course at many universities, especially those that follow the American model.
Mathematical logic
Main articles: Mathematical logic
Mathematical logic really refers to two distinct areas of research: the first is the application of the techniques of formal logic to mathematics and mathematical reasoning, and the second, in the other direction, the application of mathematical techniques to the representation and analysis of formal logic.
The earliest use of mathematics and
geometry in relation to logic and philosophy goes back to the ancient Greeks such as
Euclid,
Plato, and
Aristotle. Many other ancient and medieval philosophers applied mathematical ideas and methods to their philosophical claims.
The boldest attempt to apply logic to mathematics was undoubtedly the
logicism pioneered by philosopher-logicians such as
Gottlob Frege and
Bertrand Russell: the idea was that mathematical theories were logical tautologies, and the programme was to show this by means to a reduction of mathematics to logic.
[9] The various attempts to carry this out met with a series of failures, from the crippling of Frege's project in his ''Grundgesetze'' by
Russell's paradox, to the defeat of
Hilbert's program by
Gödel's incompleteness theorems.
Both the statement of Hilbert's program and its refutation by Gödel depended upon their work establishing the second area of mathematical logic, the application of mathematics to logic in the form of
proof theory.
[10] Despite the negative nature of the incompleteness theorems,
Gödel's completeness theorem, a result in
model theory and another application of mathematics to logic, can be understood as showing how close logicism came to being true: every rigorously defined mathematical theory can be exactly captured by a first-order logical theory; Frege's
proof calculus is enough to ''describe'' the whole of mathematics, though not ''equivalent'' to it. Thus we see how complementary the two areas of mathematical logic have been.
If
proof theory and
model theory have been the foundation of mathematical logic, they have been but two of the four pillars of the subject.
Set theory originated in the study of the infinite by
Georg Cantor, and it has been the source of many of the most challenging and important issues in mathematical logic, from
Cantor's theorem, through the status of the
Axiom of Choice and the question of the independence of the
continuum hypothesis, to the modern debate on
large cardinal axioms.
Recursion theory captures the idea of computation in logical and
arithmetic terms; its most classical achievements are the undecidability of the
Entscheidungsproblem by
Alan Turing, and his presentation of the
Church-Turing thesis.
[11] Today recursion theory is mostly concerned with the more refined problem of
complexity classes -- when is a problem efficiently solvable? -- and the classification of
degrees of unsolvability.
[12]
Philosophical logic
Main articles: Philosophical logic
Philosophical logic deals with formal descriptions of natural language. Most philosophers assume that the bulk of "normal" proper reasoning can be captured by logic, if one can find the right method for translating ordinary language into that logic. Philosophical logic is essentially a continuation of the traditional discipline that was called "Logic" before it was supplanted by the invention of mathematical logic. Philosophical logic has a much greater concern with the connection between natural language and logic. As a result, philosophical logicians have contributed a great deal to the development of non-standard logics (e.g.,
free logics,
tense logics) as well as various extensions of
classical logic (e.g.,
modal logics), and non-standard semantics for such logics (e.g.,
Kripke's technique of supervaluations in the semantics of logic).
Logic and the philosophy of language are closely related. Philosophy of language has to do with the study of how our language engages and interacts with our thinking. Logic has an immediate impact on other areas of study. Studying logic and the relationship between logic and ordinary speech can help a person better structure their own arguments and critique the arguments of others. Many popular arguments are filled with errors because so many people are untrained in logic and unaware of how to correctly formulate an argument.
Logic and computation
Main articles: Logic in computer science
Logic cut to the heart of computer science as it emerged as a discipline:
Alan Turing's work on the
Entscheidungsproblem followed from
Kurt Gödel's work on the
incompleteness theorems, and the notion of general purpose computers that came from this work was of fundamental importance to the designers of the computer machinery in the
1940s.
In the 1950s and 1960s, researchers predicted that when human knowledge could be expressed using logic with
mathematical notation, it would be possible to create a machine that reasons, or artificial intelligence. This turned out to be more difficult than expected because of the complexity of human reasoning. In
logic programming, a program consists of a set of axioms and rules. Logic programming systems such as
Prolog compute the consequences of the axioms and rules in order to answer a query.
Today, logic is extensively applied in the fields of
artificial intelligence, and
computer science, and these fields provide a rich source of problems in formal and informal logic.
Argumentation theory is one good example of how logic is being applied to artificial intelligence. The
ACM Computing Classification System in particular regards:
★ Section F.3 on
Logics and meanings of programs and F. 4 on
Mathematical logic and formal languages as part of the theory of computer science: this work covers
formal semantics of programming languages, as well as work of
formal methods such as
Hoare logic
★
Boolean logic as fundamental to computer hardware: particularly, the system's section B.2 on
Arithmetic and logic structures;
★ Many fundamental logical formalisms are essential to section I.2 on artificial intelligence, for example
modal logic and
default logic in
Knowledge representation formalisms and methods,
Horn clauses in
logic programming, and
description logic.
Furthermore, computers can be used as tools for logicians. For example, in symbolic logic and mathematical logic, proofs by humans can be computer-assisted. Using
automated theorem proving the machines can find and check proofs, as well as work with proofs too lengthy to be written out by hand.
Argumentation theory
Argumentation theory is the study and research of informal logic, fallacies, and critical questions as they relate to every day and practical situations. Specific types of dialogue can be analyzed and questioned to reveal premises, conclusions, and fallacies. Argumentation theory is now applied in
artificial intelligence and
law.
Controversies in logic
Just as we have seen there is disagreement over what logic is about, so there is disagreement about what logical truths there are.
Bivalence and the law of the excluded middle
Main articles: Classical logic
The logics discussed above are all "
bivalent" or "two-valued"; that is, they are most naturally understood as dividing propositions into the true and the false propositions. Systems which reject bivalence are known as
non-classical logics.
In 1910
Nicolai A. Vasiliev rejected the law of excluded middle and the law of contradiction and proposed the law of excluded fourth and logic tolerant to contradiction. In the early
20th century Jan Åukasiewicz investigated the extension of the traditional true/false values to include a third value, "possible", so inventing
ternary logic, the first
multi-valued logic.
Intuitionistic logic was proposed by
L.E.J. Brouwer as the correct logic for reasoning about mathematics, based upon his rejection of the
law of the excluded middle as part of his
intuitionism. Brouwer rejected formalisation in mathematics, but his student
Arend Heyting studied intuitionistic logic formally, as did
Gerhard Gentzen. Intuitionistic logic has come to be of great interest to computer scientists, as it is a
constructive logic, and is hence a logic of what computers can do.
Modal logic is not truth conditional, and so it has often been proposed as a non-classical logic. However, modal logic is normally formalised with the principle of the excluded middle, and its
relational semantics is bivalent, so this inclusion is disputable. On the other hand, modal logic can be used to encode non-classical logics, such as intuitionistic logic.
Logics such as
fuzzy logic have since been devised with an infinite number of "degrees of truth", represented by a
real number between 0 and 1.
Bayesian probability can be interpreted as a system of logic where probability is the subjective truth value.
Implication: strict or material?
Main articles: Paradox of entailment
It is obvious that the notion of implication formalised in classical logic does not comfortably translate into natural language by means of "if... then...", due to a number of
problems called the ''paradoxes of material implication''.
The first class of paradoxes involves counterfactuals, such as "If the moon is made of green cheese, then 2+2=5", which are puzzling because natural language does not support the
principle of explosion. Eliminating this class of paradoxes was the reason for
C. I. Lewis's formulation of
strict implication, which eventually led to more radically revisionist logics such as
relevance logic.
The second class of paradoxes involves redundant premises, falsely suggesting that we know the succedent because of the antecedent: thus "if that man gets elected, granny will die" is materially true if granny happens to be in the last stages of a terminal illness, regardless of the man's election prospects. Such sentences violate the
Gricean maxim of relevance, and can be modelled by logics that reject the principle of
monotonicity of entailment, such as relevance logic.
Tolerating the impossible
Main articles: Paraconsistent logic
Closely related to questions arising from the paradoxes of implication comes the radical suggestion that logic ought to tolerate
inconsistency.
Relevance logic and
paraconsistent logic are the most important approaches here, though the concerns are different: a key consequence of
classical logic and some of its rivals, such as
intuitionistic logic, is that they respect the
principle of explosion, which means that the logic collapses if it is capable of deriving a contradiction.
Graham Priest, the main proponent of
dialetheism, has argued for paraconsistency on the grounds that there are in fact, true contradictions.
[13]
Is logic empirical?
Main articles: Is logic empirical?
What is the
epistemological status of the
laws of logic? What sort of argument is appropriate for criticising purported principles of logic? In an influential paper entitled "Is logic empirical?"
[14] Hilary Putnam, building on a suggestion of
W.V. Quine, argued that in general the facts of propositional logic have a similar epistemological status as facts about the physical universe, for example as the laws of
mechanics or of
general relativity, and in particular that what physicists have learned about quantum mechanics provides a compelling case for abandoning certain familiar principles of classical logic: if we want to be
realists about the physical phenomena described by quantum theory, then we should abandon the
principle of distributivity, substituting for classical logic the
quantum logic proposed by
Garrett Birkhoff and
John von Neumann.
[15]
Another paper by the same name by
Sir Michael Dummett argues that Putnam's desire for realism mandates the law of distributivity.
[16] Distributivity of logic is essential for the realist's understanding of how propositions are true of the world in just the same way as he has argued the principle of bivalence is. In this way, the question, "Is logic empirical?" can be seen to lead naturally into the fundamental controversy in
metaphysics on
realism versus anti-realism.
References
★ Brookshear, J. Glenn (1989), ''Theory of computation : formal languages, automata, and complexity'', Benjamin/Cummings Pub. Co., Redwood City, Calif. ISBN 0805301437
★
Cohen, R.S, and
Wartofsky, M.W. (1974), ''Logical and Epistemological Studies in Contemporary Physics'', Boston Studies in the Philosophy of Science, D. Reidel Publishing Company, Dordrecht, Netherlands. ISBN 90-277-0377-9.
★ Finkelstein, D. (1969), "Matter, Space, and Logic", in R.S. Cohen and M.W. Wartofsky (eds. 1974).
★ Gabbay, D.M., and Guenthner, F. (eds., 2001-2005), ''Handbook of Philosophical Logic'', 13 vols., 2nd edition, Kluwer Publishers, Dordrecht.
★
Vincent F. Hendricks, ''Thought 2 Talk: A Crash Course in Reflection and Expression'', New York: Automatic Press / VIP, 2005, ISBN 87-991013-7-8.
★
Hilbert, D., and
Ackermann, W. (1928), ''Grundzüge der theoretischen Logik'' (''
Principles of Theoretical Logic''), Springer-Verlag.
OCLC 2085765
★ Hodges, W. (2001), ''Logic. An introduction to Elementary Logic'', Penguin Books.
★ Hofweber, T. (2004), "Logic and Ontology", ''
Stanford Encyclopedia of Philosophy'',
Edward N. Zalta (ed.),
Eprint.
★ Hughes, R.I.G. (ed., 1993), ''A Philosophical Companion to First-Order Logic'', Hackett Publishing.
★
Kneale, William, and
Kneale, Martha, (1962), ''The Development of Logic'', Oxford University Press, London, UK.
★ Mendelson, Elliott (1964), ''Introduction to Mathematical Logic'', Wadsworth & Brooks/Cole Advanced Books & Software, Monterey, Calif.
OCLC 13580200
★
Smith, B. (1989), "Logic and the Sachverhalt", ''The Monist'' 72(1), 52–69.
★
Whitehead, Alfred North and
Bertrand Russell (1910),
''Principia Mathematica'', The University Press, Cambridge, England.
OCLC 1041146
Notes
1. J. Robert Cox and Charles Arthur Willard, eds. ''Advances in Argumentation Theory and Research'', Southern Illinois University Press, 1983 ISBN 0809310503, ISBN-13 978-0809310500
2. Alfred North Whitehead and Bertrand Russell, ''Principia Mathematical to
★ 56'', Cambridge University Press, 1967, ISBN 0-521-62606-4
3. Plato, ''The Portable Plato'', edited by Scott Buchanan, Penguin, 1976, ISBN 0-14-015040-4
4. Aristotle, ''The Basic Works'', Richard Mckeon, editor, Modern Library, 2001, ISBN 0-375-75799-6, see especially, ''Posterior Analytics''.
5. For a more modern treatment, see A. G. Hamilton, ''Logic for Mathematicians'', Cambridge, 1980, ISBN 0-521-29291-3
6. S. Kak (2004). ''The Architecture of Knowledge''. CSC, Delhi.
7. McGreal 1995, p. 33
8. Morris Kline, "Mathematical Thought From Ancient to Modern Times, Oxford University Press, 1972, ISBN 0-19-506135-7, p.53 "A major achievement of Aristotle was the founding of the science of logic."
9. Whitehead & Russell, "Chapter I: Preliminary Explanations of Ideas and Notation"
10. Mendelson, "Formal Number Theory: Gödel's Incompleteness Theorem"
11. Brookshear, "Computability: Foundations of Recursive Function Theory"
12. Brookshear, "Complexity"
13. Priest, Graham (2004), "Dialetheism", ''Stanford Encyclopedia of Philosophy'', Edward N. Zalta (ed.), http://plato.stanford.edu/entries/dialetheism.
14. Putnam, H. (1969), "Is Logic Empirical?", ''Boston Studies in the Philosophy of Science''. 5.
15. Birkhoff, G., and von Neumann, J. (1936), "The Logic of Quantum Mechanics", ''Annals of Mathematics'' 37, 823–843.
16. Dummett, M. (1978), "Is Logic Empirical?", ''Truth and Other Enigmas''. ISBN 0-674-91076-1
Further reading
★ The
London Philosophy Study Guide offers many suggestions on what to read, depending on the student's familiarity with the subject:
★
★
Logic & Metaphysics
★
★
Set Theory and Further Logic
★
★
Mathematical Logic
★
Carroll, Lewis
★
★
"The Game of Logic", 1886.
[1]
★
★
"Symbolic Logic", 1896.
★ Samuel D. Guttenplan, Samuel D., Tamny, Martin, "Logic, a Comprehensive Introduction", Basic Books, 1971.
★
Scriven, Michael, "Reasoning", McGraw-Hill, 1976, ISBN 0-07-055882-5
★
Susan Haack. (1996).'' Deviant Logic, Fuzzy Logic: Beyond the Formalism'', University of Chicago Press.
★ Nicolas
Rescher. (1964). ''Introduction to Logic'', St. Martin's Press.
See also
External links
★
★ ''
An Introduction to Philosophical Logic'', by Paul Newall, aimed at beginners
★ ''
forall x: an introduction to formal logic'', by P.D. Magnus, covers sentential and quantified logic
★ ''
Translation Tips'', by Peter Suber, for translating from English into logical notation
★
Math & Logic: The history of formal mathematical, logical, linguistic and methodological ideas. In ''The Dictionary of the History of Ideas.''
★ ''
[2]'' Test your logic skills
★ ''
Logic Self-Taught: A Workbook'' (originally prepared for on-line logic instruction)
★ ''
A Brief Introductory Guide to Formal Logic'', by Dr. Hfuhruhurr
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