Logic is the study of reasoning and the process by which an argument can be determined to be logical, valid and sound. Logicians analyze arguments, premises, inferences, propositions, conditional statements, and symbolic forms.
Logic should not be confused with epistemology which explores theories of knowledge. Logic is concerned with how we reason.
Aristotle was one of the earliest philosophers to articulate principles of logic. His most famous works on Logic are: Categories; On Interpretation; Prior Analytics; Posterior Analytics; Topics; and Sophistical Refutations. Aristotle insisted that his students reason according to the Laws of Identity, Non-contradiction, and the Excluded Middle. He called these "first principles".
Other famous works on Logic include:
Francis Bacon: Novum Organum
Descartes: Discourse on Method
John Dewey: Reconstruction In Philosophy
John Stuart Mill: System of Logic
W.V. Quine, Mathematical Logic
Bertrand Russell: The Problems of Philosophy; The Principles of Mathematics
Gilbert Ryle: Dilemmas
Ludwig Wittgenstein: Philosophical Investigations
Rudolf Carnap, Introduction to Symbolic Logic and its Applications
Alonzo Church, Introduction to Mathematical Logic
M.R. Cohen and Ernest Nagel, An Introduction to Logic and Scientific Method
W.W. Fearnside and W.B. Holther, Fallacy -- The Counterfeit of Argument
As a branch of philosophy, logic has many subsets: modal logic, many-valued logic, modern logic, symbolic logic, formal and informal logic, deductive and inductive logic.
Our study of logic is designed to help the student identify fallacies. A fallacy is an invalid form of argument, and represents an instance of incorrect reasoning. There are numerous fallacies. Below is a list of common fallacies.
affirming the consequent
appeal to authority
a priori fallacies
arguing from "is" to "ought"
argumentum ad baculinum
argumentum ad captandum
argumentum ad crumenam
argumentum ad hominem
argumentum ad ignorantiam
argumentum ad lazarum
argumentum ad misericordiam
argumentum ad populum
argumentum ad verecundiam (see "appeal to authority")
argumentum ex silentio
begging the question
fallacy of false alternatives
fallacies of interrogation
gadarene swine fallacy
petitio principii (see "begging the question")
poisoning the wells
post hoc ergo propter hoc
straw man fallacy
tu quoque fallacy
Fallacies generally can be avoided by following Charles Sanders Peirce's 3 rules of reason.
"Upon this first...rule of reason, that in order to learn you must desire to learn, and in so desiring not be satisfied with what you already incline to believe, there follows one corollary which itself deserves to be inscribed upon every wall of the city of philosophy: Do not block the way of inquiry."--Charles Sanders Peirce, 1896
Related reading: Dorothy Sayers' Lost Tools of Learning; A Pragmatic Approach to Knowledge; Student Graphics Illustrate Fallacies; Logic on the Lighter Side