Published on June 15, 2007
Philosophy and Logic: Philosophy and Logic Instructor: Dr. Soraj Hongladarom Room 1025, Boromratchakumari Bldg. Tel. 218-4756; e-mail: [email protected] Course homepage: http://pioneer.chula.ac.th/~hsoraj/PhilandLogic/index.html Course Mailing List: Course Mailing List We have set up a mailing list for this course. To subscribe, send an e-mail containing the following message: Sub Philos-Logic [Your first name] [Your last name] Send it to: [email protected] chula.ac.th Objectives: Objectives Objectives To understand the basic concepts of logic and philosophy. To be able to think through the philosophical and conceptual problems clearly and cogently. To express oneselves in a coherent and persuasive manner. Textbook: Textbook Schick and Vaughn, How to Think about Weird Things, Mayfield, 1999. There will perhaps be more reading material in form of mimeographs. More on this later. Course Requirement: Course Requirement Two logic exercises 20% Midterm exam (scheduled on Tuesday, Feb. 29) 25% Two short papers on philosophy 35% Final exam (scheduled on Tuesday, May 2) 20% What is Logic?: What is Logic? Logic differs from other academic disciplines in that it studies the forms of thought, whereas the other disciplines study their own fields of study. For example, sociology studies human society; economics studies the economic relations in society Slide7: However, what logic studies in the question how to distinguish between good and bad arguments. Thus logic is a 'normative' discipline - it tries to separate the 'good' from the 'bad'. The distinction between the normative and the descriptive or the empirical. What we are concerned with in logic is: What is there in a good argument that makes it good, i.e., that makes it so compelling and forceful it is not possible not to believe it. Argument: Argument We have seen that logic studies how bad arguments differ from good ones, but then what are arguments? In order to answer this, let’s look at some examples: Suppose someone says to you: The weather is nice today - he is stating a fact. Slide9: But if he says to you: You should vote for Taksin, because he is a good guy. What is he trying to do? He is trying to persuade you to believe what he wants you to believe. And this is the essence of argument. Arguments are sets of sentences designed to persuade the listener or the reader to believe their conclusions. Form of Argument: Form of Argument Thus, to say simply that the weather is nice is not an argument. What you say this to your friend, you are not trying to change his or her mind. But if you say: 'Vote for Taksin, because he is a good guy.' You are arguing. You are not merely stating a fact. Slide11: Thus, we can see that any argument has to have two parts: The first part states what the listener should believe - the point of the argument. We call this the conclusion of the argument. And the second part concerns the reasons supporting why the conclusion should be believed. We call this the premises of the argument. Slide12: Thus, in the argument: 'Vote for Taksin, because he is a good guy.' The conclusion is 'Vote for Taksin' and the premise is 'He is a good guy.' Another example: Suppose someone says: 'All BBA students are either male or female; thus, Kanokporn is either male or female, because Kanokporn is a BBA student.' This is an argument also. Which is the conclusion? The premises? Good and Bad Arguments: Good and Bad Arguments Let’s look at this argument again: Kanokporn is a BBA student. All BBA students are either male or female. Therefore, Kanokporn is either a male or a female. If the premises are true, can the conclusion be anything but true? Good and Bad Arguments: Good and Bad Arguments Let’s look at another argument: Narisara is a BBA student. Some BBA student loves mathematics. Therefore, Narisara loves mathematics. The premises are all true, but are you compelled to accept that Narisara MUST love math because of what the premises say? Slide15: Now we say that logic seeks to establish the criteria for good arguments. Good arguments are ones whose premises establish their conclusions. We are compelled to accept the conclusions of good arguments, but we are not compelled to accept the conclusions of bad ones. Deductive and Inductive Arguments: Deductive and Inductive Arguments Look at this argument: All BBA students have to study in English. Therefore, second-year BBA students have to study in English. Apart from the question whether this argument is good or bad, there is another aspect of this argument. It is a deductive one. Slide17: Another example: One-third of the students in this room love mathematics. Therefore, one-third of the students in the BBA program love mathematics. This is a totally different kind of argument from what we have been working on. This is an inductive argument. In a deductive argument, the content of the conclusion lies entirely within the domain or the content of the premises. Slide18: But in an inductive argument, the content of the conclusion lies at least partially outside the content of the premises. Here are more examples: Deductive: If it rains, then the road will be wet It is raining now. Therefore, the road must be wet. Inductive: All the tangerines I have tasted in this basket are sweet. Therefore, all the tangerines in this basket are sweet. Truth, Validity, and Soundness: Truth, Validity, and Soundness Look at this argument: All human beings have four eyes. Nantida is a human being. Therefore, she has four eyes. The question is: If we accept the premises as true, then are we compelled to accept the conclusion? If the answer is yes, then we have to accept that this argument is valid. Slide20: Thus, a valid argument is one whose premises, if taken as true, really establish the truth of their conclusion. The premises do not to be really true. The point is that, if they were true, then the conclusion would have to be true also. However, in logic we do not want our system only to distinguish valid from invalid arguments, because we want the system to give us true conclusion, which merely valid arguments can’t guarantee. Slide21: So we introduce another criteria: An argument is sound if and only if it is valid and contains all true premises. Thus this argument is a valid but not a sound one. Why? Tunwa is a BBA student All BBA students are females Therefore, Tunwa is a female. This argument is sound (which implies that it is already valid). All BBA students belong to Fac. of Accounting. Tunwa is a BBA student. Therefore, he belongs to Fac. of Accounting. Conclusions: Conclusions Logic studies the forms of thought. It is not an empirical study. Logic studies criteria for distinguishing good from bad arguments. Good arguments are those whose premises establish their conclusion. Slide23: Inductive arguments are those the content of whose conclusion exceeds that of the premises. Vice versa for deductive arguments. An argument is valid if there is no possibility for the conclusion to be false if the premises are true. An argument is sound if it is both valid and contains all true premises.