 Hello and welcome. This is Philosophy 320, Deductive Logic, and I'm Professor Matthew J. Brown. Today I'm going to tell you a little bit about the class and how it's going to work, give you some ideas about what the class is about and the mechanics of it. I like to start class off often with a little logic puzzle to get us thinking. So let's look at this one. There are 100 senators. Every senator is either honest or crooked. At least one senator is honest, and given any two senators, at least one of them is crooked. How many senators are honest and how many are crooked? So it's a hypothetical scenario, and what I want you to do is think about all the possibilities that are compatible with these statements and figure out the answer to the puzzle. You can write down your answer now. We'll come back to the puzzle at the end of the lecture. I want to start by talking about what logic is. In everyday language, we use the term logic in a few different ways. We say something is logical to mean that it's reasonable or commonsensical, maybe. We might also talk about logic in the sense of the logic of some system or activity, the logic of this business or the logic of capitalism, the logic of war. Those aren't quite the senses of logic we mean. Logic in our sense means the investigation and evaluation of arguments and inferences. If we make an argument or we make an inference, what makes that a good or bad one? By argument, by the way, I don't mean a fight, yelling and hair pulling and stuff. I mean presenting reasons or ideas to try to convince someone of something. Now, deductive logic, which is our main focus in this class, concerns those particularly strong kinds of arguments or inferences where the truth of the premises that you start with guarantees the truth of your conclusion. We'll talk more about that in a minute. Let's look at some examples of arguments. Here's one. So premise one, if God does not exist, then life is meaningless. Premise two, if chocolate exists, then life is not meaningless. Premise three, chocolate exists. Conclusion four, therefore God exists. Now we can ask, is this a good argument? And we can evaluate that in different ways. The logical way of evaluating it tells us that yes, it is a good argument. If premises one through three were true, then conclusion four would also have to be true. Maybe you disagree with one of the premises, right? Maybe you think premise one or premise two is false. Maybe you think premises like one and two cannot be true or false because they deal with concepts that don't have that kind of meaning. But those are not logical issues. Those are issues of content, right? If you think, on the other hand, that the premises are true, then you're obligated to believe the conclusion, right? That's what formal logic tells. That's what logical reasoning general, deductive logical reasoning in general tells us. Here's another example. All whales are mammals. All mammals are hairy. So all whales are hairy. Again, this argument is a good one, logically speaking. Now you might object, whales, dolphins aren't hairy, but they're mammals. So the argument must be bad. Well, in what sense might you say it's bad? You could deny premise one, say that whales are fish. Herman Melville seems to believe that. Or you could deny premise two, say some mammals are hairy, right? But if you accept premise one and two, it seems like premise three must or conclusion number three must be right, must be true. Actually, I think the argument is right. Even whales and dolphins have hair, although sometimes just in utero before they're born and they lose it. Depends, I guess, on what you mean by hairy. Here's the third argument. All students carry a backpack. The professor carries a backpack. Therefore, the professor is a student. Now, this is a bad argument, not because the premises are false, suppose the premises are true. Suppose it's true that all students and the professor carry a backpack. Can you see why? Even if all students carry a backpack, that isn't the same as saying that all backpack carriers are students. The order matters in this kind of statement, and the order in these cases makes it such that the conclusion doesn't follow from the premises. One of the tools of formal logic is representing or translating claims in ordinary language into what we call a formal language that makes more clear the form or structure of the claim. We'll learn what the symbols I'm about to show you mean and future units, but we can translate claims like if God does not exist, then life is meaningless into a kind of schematic form. Here, I'm using G to represent God, and God exists, and M to represent life is meaningless, and then the arrow indicates the if-then structure of the statement. All students carry a backpack. We might represent with a slightly more complicated set of formal tools like this. For all X, if X is a student, then X carries a backpack. It would be how we would read that formal statement. Consider another statement like this, the person who knows the combination to the safe is not a spy. We'll learn much later in the class that the probably best way to represent this formally is a formula like this. That's complicated and maybe a little intimidating, but by the time we get to it, it will be clear to you what it means and you'll learn to do this translation work pretty easily. That's just a very quick introduction into the basic ideas that we're going to be working with in this class. Now, I want to get into some of the mechanics of it, how you're going to work your way through this class. It's an online class. We're not going to have meetings face-to-face, and so it's actually going to work a little bit more in a self-paced way, independent way, as follows. The class is divided into several units based on the core learning outcomes that we're going to focus on. To get more information about the learning outcomes, you should consult the syllabus and you'll see both the learning outcomes that you'll achieve if you make the way through the course and how they are tied to each of the units. For each unit, you need to do the readings, watch the video lecture like this one, and complete at least one practice problem set, with the exception of this unit zero has no practice problems. It's just the introduction. So for this unit, just read the syllabus, watch this lecture, and that's what you do. And this will unlock the exam for that unit. In unit one, there'll be a reading from the textbook, there'll be another video lecture, there'll be a set of practice problems. I think we've got four practice problem sets for the first unit, and then once you do that, you'll be able to take the exam. If you get a satisfactory score on the exam, and it differs per exam, but most of them it's an 80% or better score, that will unlock the next unit, and then you can start on the next unit. If you don't get that score, it doesn't mean you're done. You can retake the exam many times if you need to, although you do need to wait 48 hours and complete additional problem sets in order to unlock the next retake of the exam. So you can take all of the time you need to master each of the units, which corresponds to different learning outcomes for the course, and however far you make it indicates your level of mastery in the class. Your grade in the class is a function of how many units, and so how many learning outcomes, you gain mastery over. For example, an A in the course means that you get a satisfactory grade on all seven exams. You made it through all seven units in a satisfactory level. That's a level of mastery. An A minus is exams one through six. A B plus is exams one through five plus giving a good try on exam number six. You tried once, it was more than just a click on it and open it and submit whatever. It's a genuine attempt. The syllabus will give the full breakdown of grades and what you have to do to achieve that grade. Satisfactory, as I said, depends on the assignment, but is typically about 80% correctness. That might seem low, but the exams are not easy. And to get to that level really shows that you have basically mastered that set of concepts. Completion of an assignment, and this is most relevant for exams, but also for the practice exercises means making a reasonable effort to complete it, which could consider the number of questions answered, the amount of time taken, and the final score that you get, even though it's not satisfactory, it's better than random chance, let's say. So I'll look at your attempts closely to determine whether they meet this criterion whenever it's potentially at issue. So what do you need to do next to move through the class? You should spend some time poking around the course on D2L. Make sure you understand how it works. You should make sure to get the textbook. It's free, open access textbook, so you can download it as a PDF. You could print it. There's a print on demand. You can buy a copy of it. It's about $7 or $8 plus shipping to get the textbook. That way, it's nice because it comes bound, but that may not be important to you. If you have a good way of reading PDFs on a tablet or something, you could do that. That's okay. I don't recommend reading the textbook on your phone. I don't think the layout is very good for that. Or even on your computer screen, I think it's going to be hard to take notes and work your way carefully through the text. So I do recommend you get a hard copy or you use a dedicated sort of reader for it. You should read the syllabus carefully. Again, make sure you understand how everything works and what we're going to work through in the class. If you're interested, you should join the class Discord server. I've set this up just so there's a place where we can substitute for class discussion or conversation with your peers that you would have in an in-person class. So there's a link to join the server in D2L. If you're not super familiar with Discord, it's a pretty easy program to use. And I'd be happy to talk to you more about it in office hours if you struggle with it. And then take the practice exam that will review some of the introductory materials and unlock the first unit for you. So those are the things you need to do next. Once you've done all of those things, Unit 1 will open up. There'll be new readings, new lectures, and you'll be off to the races. I'm going to come back real quick to our logic puzzle. So let's look at that carefully. There are 100 senators. Every senator is either honest or crooked. At least one senator is honest. Given any two senators, at least one of them is crooked. How many senators are honest and how many are crooked? What do you think? What's the answer? I'm not actually going to tell you right here in the video. I want to leave it open to you to discuss on Discord and come up with your own answer. I will answer it there once enough people have weighed in. So I look forward to to seeing you in the class. I will be available during office hours that are posted on D2L. You can come see me in person, but I'll also be available on email, phone, teams. We could set up a Zoom call if that's better for you. Whatever is going to work, we can do that in office hours. I'll also answer email and other things. Of course, Discord. You can message me on Discord during my office hours. I'll also be responsive to email and Discord and so on outside of my office hours, but probably a little bit more slowly, less real time. All right. Well, I look forward to getting to know you all and good luck with the course.