 Right now you have some beliefs about what you see, where I am, even how what you see is caused. You have some beliefs about the nature of this thing, about how it came about. You have some beliefs about who you are and what you're doing. None of that is known immediately. And by that I mean that none of it is just presently conscious in your mind and just given to you as knowledge. Most of what you believe, most of what you think you know or do know, is gathered through inference. Inference is this practice or this study of taking what you already know and inferring some further truth, some further belief. You do not immediately know where I am, you are taking the evidence of what you see and what you hear and maybe even what you've seen before in formats similar to this to draw an inference about what this is, where I am and what's around me. None of you are present here and even if you were present here you would still have to make an inference about where you are, what I'm doing, what's going on in order to have knowledge about this situation. So inference is this practice, this ability, this study, however you want to call it, of being able to take what you already believe to be true or what's better known and draw a further belief, some further knowledge from what's already known. That further piece of knowledge is not immediate. You have to draw an inference. You have to draw an inference. Logic is the study of inference. And in this course we're going to study pretty much one main kind and very, very small part of one main kind of inference. So logic is the study of inference. And as I said we're going to take a look at only one kind of inference and a small part of that. The kind of inference we're going to look at is deductive inference. We're going to evaluate arguments in terms of whether they are deductively valid. Deductive validity means that if the premises are true or the reasons that you have for the conclusion, if the premises are true, then the conclusion must be true. Or another way of saying this is the truth of the premises guarantees the truth of the conclusion. The truth of the premises guarantees the truth of the conclusion. This is contrasted to inductive inference. Inductive inference means that the truth of the premises makes the conclusion more likely to be true, but it's not guaranteed. Now it's not to say that inductive inference is bad. I'm not saying it's bad. You have to use a lot of inductive inference for the rest of your life, the totality of your life. But you also use deductive inference and that's what we're going to study in this course. There's lots and lots of different kinds of deductive inference. And I don't want to scare you by starting listing them off or even even just necessarily just, you know, dive right into what we're going to deal with. But instead I want to kind of introduce it in pieces. So we're going to study in this course, we're going to look at propositions, propositional arguments, hence propositional logic. Now what this means is we got three main things, three main topics we're going to study within deductive logic. First are terms. Second is propositions. And third are the arguments themselves. So the terms. Terms are not just words. We use words all the time, but words don't really do much without meaning. Terms is that meaning that we have for these words. Specifically we're going to try to, you know, pay attention to the fact that you need one and only one meaning for a word. If you start having multiple meanings for a word, well then you're going to confuse things. And that's actually multiple terms for one word, which can be bad. So, you know, even for instance tree, right, use tree to refer to this organism right here, or even how you might chart out your family lineage, or even how you might start trying to graph out different sorts of decisions. And we use the word tree for all three of those. But in terms of, we're dealing with a term. If we're going to use term in an argument, we're going to stick with one meaning. So, we got terms. Let's take a look at propositions. Well, you can't make an argument out of terms alone. Terms combine. They combine to form propositions. Propositions are what are true or false. So, there's a stream behind me. That's a proposition. That has terms, stream and behind me. Propositions, at least the smallest proposition, is composed of a subject and a predicate. And a proposition is true just in case the subject is what's described, predicate is what's describing. And a proposition is true, an atomic proposition is true, just in case the subject is accurately described by the predicate. We're also going to have complex propositions, and this is where atomic propositions are connected with a logical connective. And a logical connective is a phrase or word that indicates a relationship between the atomic propositions or something about the truth value of both propositions. These complex propositions, and we're going to look at a lot of these, are themselves true or false. And whether the complex propositions are true or false depends upon whether the atomic propositions are true or false and the nature of their connection. Now, believe it or not, we're not going to spend a lot of time figuring out whether propositions are true or false. That's probably a whole different endeavor. There's all kinds of propositions that you're going to investigate through the course of your studies. And they're all going to use logic, hopefully. They're all going to use logic. And these different areas of studies will investigate whether these various propositions are true or false, but logic is merely interested in the study of that action, of that study, of that inference. Logic is the study of inference. It tries to answer the question, what makes a good entrance? So we're not going to spend a lot of time investigating about whether the stream was behind me. We're not going to spend a lot of time investigating what, you know, if you are who you think you are, whether 2 plus 2 equals 4, anything like that, rather we're going to look at at least some of the ways that you try to reach those propositions, try to infer those propositions through inference. So we got terms. Terms are meanings, right? And definitions are the define or don't define a term. We got propositions. Propositions are what are true or false. Okay. We still don't yet have arguments. That's next. So far, we haven't even gotten to the main object of the study of logic, right? Logic is the study of inference. What makes a good inference? Its main object is an argument. Now, arguments, so far what we looked at, it's not arguments. We've looked at terms. Terms either define or do not define. Terms are not arguments. Terms compose propositions. Propositions are what are true or false. And you might think, well, propositions, hey, that's what we're doing with arguments. No, propositions compose arguments. Like I said, the bulk of our time will not be studying whether propositions are true or false. Just merely what follows from the true or error of propositions. So propositions compose arguments. Not just any set of propositions will do. And not all propositions are created equal in an argument. So a, like I said, an argument is composed of propositions. It's composed of premises and a conclusion. Premises are what infer the conclusion. Premises are what's doing the inferring is another way of saying it. Conclusion is what's inferred by the premises. Our conclusion is what is inferred. Now, premises and conclusions, well, these had better be propositions. And these can either be true or false. But what makes them a premise versus a conclusion is not whether they're true or false. Now, I mean, it helps. The best if your premises were true. But this still doesn't, we're not going to investigate whether an argument is a good argument by just looking at whether the premises are true and the conclusion is true. That doesn't tell us whether an argument is a good argument. What tells us whether it's a good argument is the relationship between the premises to the conclusion. Okay. Now, a quick word about this. Premises should be better known than the conclusion. Premises should be better believed than the conclusion. At the very least, it should be more probable than the conclusion. Remember, the point of inference is to extend our knowledge to go from what we already know to what we don't yet know. And logic helps us do this. Logic helps us do this. So if you're reading a passage and you're trying to figure out what the conclusion is, well, one big clue is what's better known. Which sentences are better known or which propositions are better known than the other one. Now, you know, I say this because the conclusion is not always going to be the last sentence. Although most frequently conclusions can be the last sentence or the first sentence of a passage, not always. Sometimes the conclusion isn't even stated. When you look at some arguments, the conclusion is not stated and frustratingly. So what some arguments, premises are not even stated. You're going to have to learn how to figure out the difference between the premises and the conclusion, to figure out whether the conclusion is missing or whether any of the premises are missing. That's a skill you're going to have to develop because not everybody out there is a trained logician. And even some trained logicians, frankly, leave stuff out. So when we're looking at arguments, what you should be looking for is the difference between the premises and the conclusion and the relationship from the premises to the conclusion. And that's how we're going to investigate. That's how we're going to evaluate arguments.