I would really like to know what logic is. The Stanford Encyclopedia of Philosophy has TOO MANY articles on logic for someone like me. Let me list most of them: action logic, algebraic propositional logic, classical logic, combinatory logic, combining logic, connexive logic, deontic logic, dependence logic, dialogical logic, dynamic epistemic logic, epistemic logic, free logic, fuzzy logic, hybrid logic, independence friendly logic, inductive logic, infinitary logic, informal logic, intensional logic, intuitionistic logic, justification logic, linear logic, logic of belief revision, logic of conditionals, logical consequence, logical pluralism, logical truth., many-valued logic, modal logic, non-monotonic logic, normative status of logic, paraconsistent logic, propositional dynamic logic, provability logic, relevance logic, second-order and higher-order logic, substructural logic, temporal logic. I have started reading some of these articles, but I still didn't find an answer for my basic question. In some of these articles, a logic (<i>a</i> logic!) seems to be just a bunch of symbols intended to represent reasoning. But some other times I get the idea that logic intends to discover what is good reasoning. In any case, why are there so many different logics? Are they all necessary or useful? Don't computers use just one kind of logic? Truth is that if my children (6 and 8 y.o.) ask me what is logic, I don't know what to tell them....

There are "forms" of thinking and reasoning and arguing that do something very specific. They guarantee that if the premises of your thinking and reasoning and arguing are true, then so is your conclusion. These "argument forms", as we can call them, are said to be "valid". Logic is the study of these forms, and the methods used to distinguish them from invalid forms. An example? Well, what about De Morgan's theorems, one of which states not-(p AND q) is the same thing as (not-p OR not-q). This is valid, and it is worth studying, even for its intrinsic interest. And if you do study it, what you are studying is logic, or a part of it.

At the risk of a bit of self-promotion, readers might find my introductory article on logic for the Encyclopedia of Artificial Intelligence to be helpful. You can read it online at http://www.cse.buffalo.edu/~rapaport/Papers/logic.pdf.

Read another response by Jonathan Westphal, William Rapaport
Read another response about Logic