 Kind of like me right now, the world is not immediately apparent to us. We can't just simply look at the world and know everything there is to know about it and everything else. If we're going to know anything about the things around us, ourselves and each other, we have to start with what we already know and make a next step to draw a conclusion. Whenever we draw a conclusion, when we take the evidence around us and we draw a conclusion from that evidence, it's called an inference. Logic is the study of inference. And in this course, we're not going to study all there is to know about logic. We simply don't have the time. It would take an unlimited amount of time, literally. In this course, we're going to look at three parts of deductive inference, three parts of deductive logic. We're going to look at terms, propositions and arguments. So remember, we're going to distinguish between terms, propositions and arguments. A term, that's the smallest unit of this, a term is a word that's used for one and only one meaning. A term is a word that's used for one and only one meaning. Now, don't confuse a term for the word itself. Words have many different meanings. But a term, a word, there's a collection of letters or sounds. Tree, apple, sky, these are all words. Terms would be what we mean by tree, apple and sky. So I've said that a term is a word with one and only one meaning, or a word where we use one and only one meaning. Immediately, you might wonder, wait, what the heck, don't words just have one meaning? Well, no, as a matter of fact, words have lots of different meanings. If you look at the dictionary, you're going to find quite a few definitions for any given word. The last time I looked, the word innocent had something like 16 definitions. It's not exaggeration, something like 16 definitions. It's not infrequent, it's not unusual for us to use a word in more than one way, even in the discourse, sometimes we're not even aware of it. We could talk in maybe simple ways or poetic ways, or you could talk about the word blue. The word blue can be used either to describe a color or a person's mood, and sometimes both. Sometimes you use them interchangeably at the same time. It can get a little confusing, it can get a little confusing. So, yeah, a term is a word used with one and only one meaning. Well, next up we have propositions. Propositions are composed of terms. They're not terms, but they're composed of terms. When you put the terms together to create something that's either true or false, that's a proposition. So not just any combination of terms counts. Blue, B Wood, bookshelf unit. Well, that's a combination of terms, and maybe there's a meaning for each of those. But you haven't expressed something that's either true or false. In fact, I've expressed something that's pure nonsense. On the other hand, something like, I am walking on a path. That's a proposition that expresses something true, and it's composed of terms. So, not just any sensible combination of terms creates a proposition. What time is it? Shut the door. These are both sentences. The first is an interrogative, right? Ask a question. The second is an imperative, right? It gives a command. But neither one expresses something that's either true or false. Somebody said, what time is it? You said, false. That would be weird. You get a reaction of confusion at the very least. Somebody says, shut the door. And you said, that's false. Again, especially depending on who's telling you, you get probably maybe not the reaction you're looking for. So, not just any combination, sensible combination of terms expresses a proposition. Propositions are only what is true or false, right? So, there are trees behind me. That's a proposition. That's a sensible combination of terms that expresses something that's true, namely that there are trees behind me. There is an elephant behind me. That is also a proposition, but it's false. It's still a sensible combination of terms that expresses something true or false, and in this case, false. So, yeah, a proposition is composed of terms, and it's what's true or false. So, just as propositions are composed of terms, arguments are composed of propositions. So, terms are words that are used for one and only one meaning. A proposition is a combination of terms that composes something that's true or false. And an argument, well, an argument is something different. That's different from either propositions or terms. This brings us to arguments. So, terms compose propositions, and propositions compose arguments. Now, the way this works is one collection of propositions will infer another proposition. Now, strictly speaking, with deductive inference, there can literally be an infinite number of conclusions, but let's just leave that aside, right? For the sake of discussion, let's just assume for you right now that we're dealing with only one conclusion at a time, right? So, you have one set of propositions inferring another. That's an argument. That's an argument. Not just any collection of propositions will do. It has to be that one set of propositions infers another. Now, arguments are composed of two parts. The premises and the conclusion. The premises are those propositions that infer the conclusion. The conclusion is what's inferred by the premises. The premises, in some sense or another, you know, this is debated, but in some sense or another, make the conclusion true or they justify the conclusion. They either make the conclusion true or they justify the conclusion. That's, in some sense, they make it true, right? And in turn, the conclusion, in some sense, is made true or is justified by the premises. So, the premises infer the conclusion. Now, again, simply for the sake of explanation, because we're not going to go into this in too much detail, broadly speaking, there are two kinds of arguments, right? There are inductive arguments and deductive arguments. Now, inductive arguments are arguments where the premises make the conclusion more likely to be true or more probable, right? And deductive arguments are arguments where the premises, the truth of the premises, necessitates the truth of the conclusion. In other words, with deductive arguments, if the premises are true, the conclusion must be true. With inductive arguments, all the premises can be true and the conclusion falls. Now, I don't want to jump too much into this because it's a long explanation of the history of logic and philosophy. Inductive arguments are not necessarily bad, right? They give us a lot of really great kinds of knowledge. So, for instance, all of scientific inference is based upon inductive reasoning. Moving from evidence to conclusion and scientific inference is inductive, not deductive. Whereas an example of deductive inference that you might be familiar with would be mathematics. Mathematics. So, if you deal with probability, that's inductive. If you deal with necessity, that's deductive. I mean, these are all different ways of describing it. One is not necessarily more accurate than the rest, but hey, it's a start. So, premises and conclusion. These compose arguments. The premises in some sense necessitate or justify or make the conclusion true. The conclusion is in some sense made true or justified by the premises. Well, spotting the difference between inductive arguments and deductive arguments, it's not really important at this point. Probably wanting to get to it really during the course of the semester. Like I said, we're only going to be dealing with deductive arguments. Now, spotting the difference between inductive and deductive arguments, not really important at this point, but spotting the difference between the premises and the conclusion is. You have to be able to identify the difference between the premises and the conclusion if you're ever going to understand any argument, including ones that you hear outside of this course. And I've noticed this that sometimes people are very sloppy with the difference between the premises and conclusion. And they don't really know which to address in discussions. Okay. Now, sometimes, like I said, arguments are collections of propositions, which means, grammatically speaking, that pretty much always going to look like a paragraph, right? Or a series of paragraphs. Now, in these paragraphs, you're going to find, or at least sometimes, you'll find little Q words. And sometimes these Q words are used for the conclusion and sometimes they're used for the premises. It's rare that you're going to have somebody be nice if they always did this, but it's rare that you're going to have somebody who writes a paragraph saying, for all the reasons I've just provided, I conclude this. You know, it doesn't always happen. It'd be nice if it didn't, but it doesn't always happen. Similarly, you know, I believe this, for these reasons, in one, two, and three, right? It makes for very clear writing if you do that. Somebody can never be mistaken, or not never, but it'd be really hard to be mistaken about what somebody is doing if they actually, you know, did that, but it's not always. So we don't always have these nice full sentences that are telling us exactly what's going on. Instead, there's usually some little Q words. So for conclusions, you'll find Q words like, therefore, so, thus, in conclusion, in summation, right? Actually, in summation isn't always used. That's probably not a good word, good phrase for conclusions. But, you know, these little Q words, right? So it's gray outside, it's slightly cool, and the barometer is dropping, dropping. The barometer is dropping. For these reasons, right, I conclude it is going to rain. Now, that'd be a nice long, drawn-out way of saying it. Almost never happens. Instead, it's something like, wow, you know, the temperature's dropping, it's cloudy, the barometer's dropping. So it's gonna rain, right? That little so, right? That's your Q word, that that's the conclusion. There are also sometimes Q words for premises, right? Sense for, because, right? So to take that same example, say, it's gonna rain since the barometer's dropping, the temperature's dropping, and it's getting more cloudy. That little Q word, sense, that indicates the premises. For that short little, very bad argument. Now, these Q words, these are gonna be helpful in finding the difference between the premises and the conclusion. And as I said, it is necessary to find the difference between the premises and the conclusion. However, these Q words can't replace your ability to comprehend. Now, if you do, you're gonna be fooled for the rest of your life. Now, these Q words can be helpful, at the very least it can be helpful in ascertaining the framework of the author's mind. But you should also not let the Q words replace your ability to reason. You have to comprehend what's provided for you in writing better than the author has written it. This is just a sad fact of life. You have to comprehend better than the author who's provided it. Now, like I said, these Q words, sometimes these Q words aren't going to be there, and sometimes they're gonna be there badly. So, you have to comprehend, you have to understand the meanings of the terms to figure out the difference between the premises and the conclusion. So, take a look at this set of propositions. So, as I said, these paragraphs aren't always going to have word cues to indicate what's the, you know, which are the premises of which the conclusion, and they are sometimes maybe they're just labeled very well. So, you have to, you know, word cues are nice, they're helpful, but they can't replace your ability to comprehend and understand what's going on in the paragraph. So, you look at these sentences here, right? I have them out of order, purposely have them out of order as far as, you know, which one is the conclusion, right? They just put it at the bottom. You also shouldn't think that the conclusion is always just going to be the last sentence. That isn't the case, right? But, you know, just looking at these sentences here, right, what can you tell from them looking at these? We never know that any of our perceptual beliefs are true. We are sometimes mistaken in our perceptual beliefs. If we are sometimes mistaken in our perceptual beliefs, then we never know that any of our perceptual beliefs are true. Okay. Well, what do you notice right away about these propositions? Does one seem like it really needs to be proven? You know, is it more, how should we say, implausible than the rest? What's the structure of the sentences? How do they relate to each other? You know, whether a proposition is a premise or conclusion, it's going to depend upon the relationship it has to the other propositions. See, we just look at these. Which one of these looks the most likely to be true? Well, you know, we're sometimes mistaken in our perceptual beliefs. Well, yeah, that happens a lot, right? We make mistakes about colors or shapes or whether, you know, whether or what the thing is off in the distance. That's the most probable thing. If it's the most probable thing, then yet chances are it's going to be a premise. Because the conclusion is going to depend upon the premises. Well, you know, if that's a premise, well, look at that third proposition there. It has the first part of that third proposition is that, you know, we are sometimes mistaken in our perceptual beliefs. And then according to that, you know, that third proposition, well, if that's true, then we never know that any of our perceptual beliefs are true. Okay. You know, maybe you don't necessarily buy that, but you know, it's at least a link between that second proposition and the first proposition. It's the, you know, kind of direction of the argument there, right? So it's that first proposition here. You know, we never know that any of our perceptual beliefs are true. That's the conclusion. The last two are supposed to be premises, evidence for that first proposition. And that's just given by the structure of the argument, the relationship of the premises to each other and, you know, which proposition is the most plausible of the rest? Well, spotting the difference between premises and conclusion, that's one essential skill in dealing with logic. Another essential skill is spotting whether you're actually dealing with an argument, right? Just as not any, you know, not every, excuse me, not every sensible collection of terms, composes a proposition. Not every sensible collection of propositions, composes an argument. There are lots of different kinds of paragraphs besides arguments. There's, you know, simply statements of belief, right? People just kind of expounding what they believe. The lovely day, the temperature is nice, nice and cool. I'm not sweating. I have, there's no rain to ruin my day. And I enjoy the cloudiness because of, you know, decrease in illumination. Right. Maybe I'm just talking about how much I'm enjoying the day. There's no argument there. There's no inference from premises to conclusion. It's just me simply talking about my day. And people do this a lot and kind of mistake it for an argument. They just sit there and say, this is what I believe. And they start really, therefore you must believe this too. Like, well, why? You've just told me what you believe. You haven't given me a set of evidence. You haven't given me evidence for a conclusion. You know, sometimes people are, like I said, sometimes people are just providing statements of what they believe. They're being funny. They're telling a humorous story. Humor is not an argument. It's unfortunate that in today's day and age we get persuaded by humor quite a lot. But humor is not an argument. We think, aha, that person's witty. They made something funny, therefore they said something truth. No, that doesn't work either. Sometimes, well, there's a big difference between an argument and an explanation. Even though, by the way, they kind of look structurally the same as far as paragraphs are concerned. Remember those Q words that I mentioned? Well, sometimes Q words are used for the conclusion of an explanation. You know, the temperature, you know, we say something like, well, okay, so let me just start this way. An explanation is different from an argument. An argument is supposed to persuade you of the conclusion. The premises are supposed to justify the conclusion. That somehow make the conclusion true. An explanation is not like that. An explanation doesn't justify its conclusion. It's not really conclusion. I'm just doing this, you know, it's a scary question on the mind. It's not its conclusion. The premises don't justify, the evidence doesn't justify the conclusion. Rather, with an explanation that explains why the conclusion. Not whether the conclusion, but why the conclusion. So, explanations presume the conclusion is true. And what's given is simply an explanation for why. You know, why it is the case. So, for instance, I've got this tree here, right? I can say something like this. I could say a seed fell on the ground, germinated, took root in the soil through a process of nutrition, hydration and, you know, shade and proper environment that the tree came to be. None of you doubt that the tree exists, right? It's right here. None of you doubt that the tree exists. What I provided is not a justification that the tree exists. If I were to say, I will prove this tree exists, you say, what? That's a little crazy. If I said instead, I will explain how this tree came to be. Okay, well that's an explanation. So, explanations presume the conclusion is true. Now, suppose I did something different. Suppose I said, I will prove to you that this tree has been around longer than San Antonio, Texas. That's probably going to need some evidence, right? You're going to need some kind of justification for that. Yeah, it might be the case that some of the people watching this video are familiar enough with botany where you understand this right away or, you know, you can understand those trees right away. I have a very poor grasp of the age of trees, but I think this tree is somewhere around 20 or 30 years old. It's not older than the San Antonio, Texas. If I were to claim that I could prove that it's older than San Antonio, Texas, well that would be an argument. That conclusion is, that's something that really needs to be proven. Even my claim that this tree is 20 or 30 years old, you're probably still at this point saying, I want to know why that's true. I want to know what evidence or justification you have for that. Now maybe all of a sudden you're interested in the age of trees. So spotting, as I said earlier, spotting the difference between premises and conclusion is an essential skill. Spotting whether you're in fact dealing with an argument as opposed to some other kind of paragraph or series of paragraphs, that's also an essential skill. That's also an essential skill. So, hey, let's take a look at a few examples. So the exercise here is to determine whether this is an argument. Well, let's take a look at this paragraph. So we're just kind of reading it over, right? Does anything strike you as maybe the conclusion or the point or what they're trying to get you to believe for this particular paragraph? We have organisms sinking into deep water means death. Plant cells can't photosynthesize fish. And other animals lose contact with the surface food supply. And then they become food for estranged deep living predators. That's a frightening phrase. It's an estranged deep living predators. It's a little scary, actually. I didn't realize the logic class was going to be frightening in this way. Well, which of these sentences are supposed to, I don't know, which propositions lead to a point to or justify the others? Well, it's not that, you know, plant cells can't photosynthesize. It's somehow justified by fish and other animals that descend, right? It's not like the second proposition is justified by the third. And it's not even justified by the first, either. I mean, maybe that would be an example. The second proposition might be an example of the first, but it's not justified by the first. Same thing goes with the third one, right? The second or the first proposition. In fact, it's that first proposition that is, you know, kind of being led to by the second and the third, right? This is the main point. Organisms at the sea surface, sinking into deep water usually means death. Okay. Now, okay, so this really looks like it's the main point of the paragraph. Is it an argument? Do you need to be persuaded of the fact? Does this need to be justified by the other two? Well, no, right? We can just simply observe organisms at the sea surface, sinking into deep water, right? That's not hard to figure out, right? We just observe them doing this. How do we justify that organisms at the sea surface, you know, they sink and that usually means we watch it happen. The second and the third proposition in this paragraph are explaining or giving examples or, you know, trying to illustrate the first, right? So this isn't an argument. It's an explanation. It's an explanation. Let's take a look at another one. Okay, so here we have a statement about young people at universities trying to achieve knowledge, not learn a trade. We all must learn how to support ourselves, but we must also learn how to live. We need a lot of engineers in the model world, but we do not need a world of modern engineers. Okay. Now, is there a conclusion, right? I mean, point for all of this. Is one of these propositions infer, or does some of the propositions infer the remaining? I mean, we've got three propositions here. I would be impressed if you have a, you know, one of these propositions is actually a conclusion. Now, at best, right, this is an explanation. And even then, I wouldn't, I don't even think it's an explanation. It looks like a statement of belief to my eyes. We've got three propositions here. They're really not related to each other, right? They're almost, each one is almost a rephrase of the main point of the other two. Slightly different take on it, but yeah. There's not even an explanation here. This is just a statement of belief. So when you're reading these, you know, reading your paragraphs, trying to read passages, you know, one essential skill, as I said, one essential skill is to find the conclusion. And another essential skill is to figure out whether you even have an argument here. Well, to sum up, we've looked at the definition of logic. We looked at the three parts of logic. Two kinds of arguments. The difference between premises and conclusion. The, even the difference between arguments and other kinds of paragraphs or series of paragraphs. And we've even had a little bit of practice ourselves. We looked at a few examples. So your next step is to practice, right? Take the exercises that are provided through the course. And, you know, make sure you are able to spot the difference between the, or you know the difference between these different parts. So practice, have fun, and I'll see you next time.