³1username³2LarrySanger³2name³2text_default³2version³21³2ts³2981078927³2ip³224.234.246.58³2data³2newauthor³31³3minor³30³3text³3Today we’re going to study a subdiscipline of philosophy called <i>logic</i>.  This is basically the study of argument -- by which we mean, not angry disagreements or fisticuffs, but instead <i>the</i> <i>giving</i> <i>of</i> <i>reasons</i> <i>to</i> <i>believe</i> <i>things</i>.  So recall from last time the definition of "argument":

An <i>argument</i> is a set of statements, one of which (the <i>conclusion</i>), it is said or implied, follows from the others (the <i>premises</i>).

It’s extremely important in this class that you understand what arguments are, and that you distinguish them from other things.  To give an argument is to give evidence, and then draw a conclusion from it; it is to give reasons to believe something, and then to state the belief.  The statements that give expression to the evidence, or the reasons, are all called the <i>premises</i>.  The thing one argues <i>for</i> is called the <i>conclusion</i>.  You can think of a whole argument as a set of statements, comprising premise or premises, and the conclusion.

Now, there are <i>other</i> kinds of sets of statements besides arguments, such as explanations.  Logic does not, or not primarily, concern itself with explanations.  For example, suppose I offer an explanation for why there are tides: I talk about the gravitational effect of the moon and the sun on the oceans, and so on.  Now, <i>that</i> isn’t an argument.  It is an <i>explanation</i>.  In <i>that</i> case, I’m explaining why there are tides.  I’m not trying to convince you <i>that</i> there are tides.  We have already agreed that there are tides.  The question the explanation answers is <i>why</i> there are.

On the other hand, suppose I argue for the following claim: "God exists."  In other words, "God exists" is the conclusion of an argument I make.  In that case I am <i>not</i> explaining why there is a God.  If I tried to explain why there is a God, I would be <i>assuming</i> that there is a God.  But if what I’m doing is <i>arguing</i> for the existence of God, then I’m not <i>assuming</i> that he exists; rather, I’m trying to <i>convince</i> you, or a skeptic anyway, that God exists.

So I think you can see the difference between an argument and an explanation.  On the one hand, the function or purpose of an argument is to convince people who might be doubting the conclusion.  On the other hand, the function or purpose of an explanation is to give the cause of some phenomenon which we observe, or are willing to assume actually occurs.  To put it even more briefly, the purpose of an argument is to <i>persuade</i>, while the purpose of an explanation is to <i>explain</i>.

Just as a hammer is the tool of the carpenter’s trade, an <i>argument</i> is the tool of the philosopher’s trade.  And, as I said last time, it shouldn’t be too hard to see why philosophers work so much with arguments: philosophers carry to heroic lengths the human tendency to doubt sometimes the deepest, most fundamental of our beliefs.  Because they want to overcome all of these doubts, they offer and examine arguments for various claims: the arguments are supposed to be what will rid us of the doubts.  If we accept what we know is an excellent argument for a conclusion, and we’ve refuted all the plausible arguments <i>against</i> that conclusion, then we’re very well-positioned to say that we <i>know</i> that the conclusion is true.  Arguments, then, have the potential to give us  <i>knowledge</i> and to rid us of doubts; that’s why arguments are so important.

But just as there are good and bad hammers, there are good and bad arguments.  In fact, I imagine that there are a lot more bad arguments in the world than there are bad hammers.  Let me give you an example of a bad argument.  Suppose I wanted to argue for the claim that <i>all</i> <i>killing</i> <i>is</i> <i>wrong</i>.  And suppose I was giving this argument to a bunch of people who supported the death penalty: they think that <i>some</i> killing is fine, as punishment of the worst murderers, say.  So I argue as follows:

If one should never do X, all X is wrong.  (X can be any action.)

One should absolutely never kill.

Therefore, all killing is wrong.

Would the supporters of the death penalty be impressed by this argument?  Of course they wouldn’t.  They would say, "You’re begging the question.  In your argument, you say that one should absolutely never kill.  But to prove <i>that</i> you’d have to prove that all killing is wrong -- which is what you’re trying to argue for.  We disagree with your conclusion: we think that <i>some</i> killing is <i>not</i> wrong.  And so of <i>course</i> we are going to disagree with your premise, that one should absolutely never kill.  No indeed, in some cases one actually <i>should</i> kill: it’s our grim duty, an unfortunately necessary part of justice."

So you can see that my argument just isn’t going to work against those people.  In it, I presuppose the conclusion: in other words, one of the premises <i>assumes</i> that the conclusion is true.  This is an error in arguing.  The <i>kind</i> of error has a name: <i>begging</i> <i>the</i> <i>question</i>.  If my argument begs the question then in my argument I assume the very thing that I’m trying to argue <i>for</i>.  Of course an argument that begs the question won’t, or shouldn’t, convince anyone: if I assume what I’m arguing for, anyone who assumes differently will be unimpressed.

Begging the question is one of the ways that arguments can go wrong.  There are many, many other ways; and those most common ways that arguments can go wrong are called <i>fallacies</i>.  So begging the question is one kind of fallacy.  You should make sure that you are not committing any fallacies yourself, when you argue.

Let me give you another example of a fallacy.  Suppose I argue like this:

Ted is a good tennis player.

Therefore, Ted is good -- a morally good person.

Here the problem is that the word "good" has different meanings, which is to say that it is an <i>ambiguous</i> word.  In the premise, we say that Ted is good <i>at</i> <i>some</i> <i>particular</i> <i>activity</i>, in this case tennis.  But in the conclusion we say that Ted is a <i>morally</i> good person.  Those are clearly two different senses of the word "good."  And so of course the premise might be true, while the conclusion would still be false: Ted might be the best tennis player in the world, but a rotten person morally speaking.  Appropriately, since it plays on an ambiguity, this sort of fallacy is called <i>the</i> <i>fallacy</i> <i>of</i> <i>ambiguity</i>.

Now you’re just going to have to trust me that there are zillions of other fallacies.  Whole books have been written cataloging fallacies -- all the different kinds of ways that arguments can go wrong.  Today we’re going to be less ambitious: we’re going to outline, in broad generalities, how arguments can <i>go</i> <i>right</i>.  In other words, I’m going to introduce you to the study of <i>good</i> arguments, non-fallacious arguments -- which is to say that I’m going to introduce you to <i>logic</i>.

Here is a definition of "logic":

<i>Logic</i> is the study of good arguments and definitions; in particular, it is the study of (1) forms of arguments and their parts, (2) the qualities (of arguments) of validity, cogency, and soundness, (3) how to construct, identify, interpret, and evaluate various kinds of arguments, and (4) how to construct and evaluate definitions.

Traditional treatments of logic have included discussion of not just arguments, but the varieties and standards of definitions, as well.  And the way I’ll present it, logic will include discussion of <i>both</i> arguments <i>and</i> definitions.

I want to introduce you to some of the most fundamental logical concepts, for two reasons.  The first is that logic is one of the basic branches of philosophy, and so if I’m going to introduce you to all, or almost all, of the basic branches of philosophy, I’d better introduce you to logic.  The second reason is practical: namely, logic will help you understand better the rest of philosophy.  So it also has practical value.

There is a good reason why logic will help you understand the rest of philosophy.  I said last time that it is doubt about the meaning and justification of certain fundamental beliefs that motivates us to do philosophy.  Well, very often to extricate us from these doubts what are needed are <i>definitions</i> that explain the meaning of our basic concepts, and <i>arguments</i> to justify, or give reasons for, various beliefs that we’re not quite sure about.  Logic states the standards of good definitions and good arguments: it gives us the tools to see whether various proposed definitions, or arguments, are any good or not.  It helps us to avoid fallacies.

So let’s go back to the definition of "logic" I gave, and examine its various parts, leaving aside part (4), about definitions, for now.

Logic, like mathematics and physics, has a theoretical part and an applied part.  Parts (1) and (2) of the definition together describe the theoretical part of logic, and (3) describes the applied part.  And just as a nonmathematician learning physics should study mathematics in order to <i>use</i> or <i>apply</i> mathematics well, a nonlogician in <i>any</i> task that requires reasoning, such as confirming rational beliefs, should study logic to learn how to <i>use</i> or <i>apply</i> logic well.  Moreover, like mathematics and physics (and many other things), you have to do quite a bit of <i>practice</i> if you want to gain any facility in using logic.  Logic is a bit unlike other parts of philosophy in that way: in studying books in <i>other</i> areas of philosophy, such as ethics and metaphysics, you’ll rarely see <i>problems</i> at the end of the chapter.  But you might very well do problems in logic, in order to learn how to use logic.  (Of course, that’s not to say that practice, of various sorts, would not help one to learn other areas of philosophy better.  It’s just that the practice would be practice thinking the problems through.)
³3summary³3* Ch. 2, sect. 1³2tscreate³2981078927³2keepts³2981084843³2id³21001³2host³2dhcp058.246.lvcm.com³2revision³21