What is logic and why do philosophers study it?

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Much of the time philosophers study what other people take for

granted. They ask "Why?" and "How?" when others are content to

accept what seems obvious and in need of no justification.

Philosophy thus involves explanations, arguments, and their

critical evaluation. Here argument is meant not in the sense of

dispute or controversy but in the sense of "arguing (for or

against)", or "making a case (for or against)".

In evaluating arguments and explanations two features are

significant: whether the premises, the "starting points", are

jointly plausible; and whether what is said to follow from them

does so. When we reflect on these features we arrive at logic: the

systematic study of what follows from, and of the relations that

hold within and between, bodies of belief, loosely speaking.

(Loosely speaking, for in logic we are not so much concerned with

what we do accept or believe rationally and what inferences we in

fact make but with rather what one could so accept or believe and

what inferences one would be warranted in making whether or not

one actually does so.)

As an attempt at a systematic theory logic has to start somewhere.

Its "raw data" are our intuitions, our inferential practice, and

our reflective judgments. Now, we have no guarantee that these

cohere well: in fact there are tensions. At the very least, we may

find it difficult to construct a systematic account that

accommodates all, or even most, of the raw data. A systematic

theory may therefore lead us to refine (i.e. revise) our

intuitions and change our practice. Logic is a much less

cut-and-dried affair than many text-books suggest.

Formal logic constitutes a "body of knowledge", not in the sense

that all its findings are incontrovertible facts but somewhat in

the same way as moral philosophy does: in each case there is a

standard set of concepts, theories involving those concepts, forms

of argument and a ragbag of tricky cases that is played off

against intuitions, and perhaps used to subject those intuitions

to critical scrutiny and to refinement. Formal logic is also more

like the sciences than is any other part of philosophy: it aims at

a systematic account of a body of "phenomena" on which there is

fairly widespread agreement and in order to do so it uses formal

methods of representation (a feature of logic that goes back to

the ancient Greeks) and formal techniques. Formal logic is formal

in that it seeks to give a systematic account of the validity of

individual arguments only insofar as they exemplify certain

"patterns of argument". Patterns, or forms, of argument are the

main object of study. It is this feature of logic that allows us

to establish some results in and about logic with the same

exactness as one encounters in mathematics (but at least when

logic is studied as part of philosophy one should not lose sight

of the wider goal).

Two further considerations are often given as reasons for studying

logic:

1. Logic is "therapeutic": one learns logic in order to become better

able to recognize and to construct good arguments (in philosophy

or any other discipline).

2. Formal logic is an indispensable item in the contemporary

philosopher's toolkit.

Learning about any systematic discipline improves one's own abilities

in thinking systematically. And certainly, the methods and techniques

of formal logic are used by some philosophers, mostly those working in

philosophy of language and philosophy of science. Two text-books that

integrate formal logic into a range of topics in philosophy are

Brenner's Logic and Philosophy and Bradley and Swartz's Possible

Worlds.