PHIL 201DEDUCTIVE AND INDUCTIVE LOGIC TRANSCRIPTS1:Hello, and welcome to another presentation for Philosophy 201: Philosophy and Contemporary Ideas. I am Dr. Mark Foreman, and I want to continue in this presentation our discussion of logicby discussing the distinction between deductive and inductive logic. Both of these are acceptableforms of reasoning that we use in philosophy, but they arrive at different kinds of conclusions. Solet’s look at their differences.S2:Let’s first discuss deductive arguments. Deductive argument is a form of logic made up of arguments where, if they are valid, the conclusion follows necessarily from, or is guaranteed by, the premises. Other terms we say, when we talk about this, we say, that if the conclusion is logically certain it’s impossible for it not to be true. Assuming of course that the premises are true here.Deductive arguments are judged as valid or invalid. Those are the only two categories we have. It is either a valid argument or it is an invalid argument. We don’t have partially valid or mostly valid or mostly invalid types of arguments in deductive logic.A valid deductive argument is one where, if we assume the premises are true, it’s impossible for the conclusion to be false. And that’s very important in understanding that. If the premises are assumed to be true, the conclusion must be true; it is logically certain.Now, the formal procedure for writing out a deductive argument is what we call a syllogism. Every syllogism has two premises and a conclusion. But there are different types of syllogisms. Let’s talk about those.S3:There are three kinds of deductive syllogisms. These are based actually on the kind of proposition that each of the syllogisms uses. A proposition is simply a statement that has two elements to it. First of all it makes a claim about reality; it affirms or denies that something is real. Second of all, it has truth-value; it’s either true or it’s false. Now there’s three kinds of propositions and that leads to three kinds of syllogisms.The first kind is what we call a categorical proposition. This simply relates two things together intwo terms or two categories: subject and predicate. And we have a syllogism that uses categoricalpropositions. Here’s an example.‘All LU students are attractive. All attractive persons are smart. Therefore, all LU students are smart.’Page 1 of 5PHIL 201If the two premises are true – that all LU students are attractive, and, all attractive persons are smart – then in fact it must be true that all LU students are smart. That has to follow. It’s impossible for that to be false, if those two premises are in fact true.A second kind of syllogism is what we call the disjunctive syllogism. It uses a kind of proposition called a disjunctive proposition. This is a proposition that presents two alternatives tous, in the form of an either-or statement. Here’s an example of a disjunctive syllogism.‘Either it rained or I left the sprinkler running. It did not rain. Therefore, I left the sprinkler running.’If we assume that the first premise is true, that either it rained or I left the sprinkler running – thatmeans that those are the only two alternatives that are there, there are no other alternatives, that’swhat it means to say that that is true – and if we assume that the second premise is true, that it did not rain, then we’ve eliminated one of the two alternatives, and the only one left is the other alternative, that I left the sprinkler running. So if it is truth that either it rained or I left the sprinkler running, and if it is true that it did not rain, ten it must be true that I left the sprinkler running. That has to be true, it’s impossible for it to be false, assuming that those first two premises are in fact true.A third kind of syllogism is again based upon a third kind of proposition called a hypothetical proposition. A hypothetical proposition is a proposition given in the form of an if-then: if A, thenB. And we can use that also in an argument. There’s different kinds of hypothetical syllogisms we can have, but I’m just going to supply one here. You can look at some other ones inside your book there.This proposition says: ‘If you do the work, then you will pass the course. You did the work. Therefore, you passed the course.’Now notice what’s happening in our first proposition here, our first premise. It’s making you a promise: if you do the work then you will pass the course. If that’s true, then that is a promise, a guarantee to you. Our second promise tells us that in fact you did the work. Therefore it must be true that you passed the course, assuming that our first premise is true – that if you do the work then you will pass the course. It’s impossible for that conclusion to be false. That’s what a hypothetical proposition will do.Those are different kinds of deductive syllogisms. Now each of these of course has rules that govern these syllogisms and how you can do them. And if you break those rules the syllogism will become an invalid syllogism. Some of these are given in your book. For the purposes of our presentation here, I’m not going to go through all the rules. I want to move on now and talk about inductive arguments.S4:An inductive argument is a very different beast than a deductive argument. Although again it’s a very normal way that we reason about things, and it certainly is a way that we do logic here.Page 2 of 5PHIL 201Inductive argument is: logic made up of arguments that can lead only to a probable conclusion, not a necessary one. You might remember when we talked about our deductive arguments we said that if the premises are assumed to be true, the conclusion must be true, in a valid deductive argument. That’s never the case with an inductive argument. Even if you have a very, very stronginductive argument, you never get to a conclusion that must be true. The most you can get to is a conclusion that is probably true, or, very probably true – but never certainly true, not in the senseof logically certain. Maybe we can use the term practically certain, but not logically certain. And that’s why we say no inductive argument can arrive at an absolutely certain conclusion, not in a logical sense. You may wonder, why is that? Well deductive arguments are based on structural relationships, and therefore we can say whether they are valid or invalid based upon the structural relationships. But