 You don't take advantage of your city's parks and natural areas. You're doing yourself a disservice. You got to take time out every once while experience all this life of gloating enough rant. So we're talking about deductively valid arguments. Now the word valid is used in quite a few different ways in today's society. We usually mean valid like in a kind version of this. We mean something like I can see why you'd say that. Maybe how shall we say more forceful use of the term is especially we say that's that's not a valid point. We're saying something to the effect of I disagree with that point to the extent that you shouldn't believe it either. That might be a mischaracterization. Well we don't mean this. We don't mean this sort of thing. We're talking about an argument being valid in logic. Logic does not deal with preference of beliefs. It deals when we're talking about deductive validity. We're talking about the relationship from the premises to the conclusion. We've seen terms. Terms are not valid or invalid and by the way, terms are neither true nor false right. Terms either defined or well defined or not well defined. We've seen propositions. Propositions are either what's true or false but propositions are not arguments. Arguments are composed of propositions but they are not themselves arguments and arguments are neither true nor false. Arguments are either valid or invalid and validity is not talking about preference of belief or approval anything like that. What validity is dealing with is the relationship from the premises to the conclusion. Well I said that validity deals with the relationship of the premises to the conclusion and the relationship is this that the truth of the premises necessitates the truth of the conclusion or another way of saying this is if the premises are true then the conclusion must be true or yet one more way of saying this is it's impossible that the premises all the premises are true and the conclusion is false. So there's three ways of saying this the truth of the premises necessitates the truth of the conclusion. If the premises are true the conclusion must be true or it's impossible that the truth that all the premises are true and the conclusion is false. So as I said this has nothing to do with preference of beliefs or even you know being able to identify with somebody's beliefs it's not that it's a relationship from the premises to the conclusion. Now we want to be careful to avoid some misconceptions. So here's an example of a deductively valid argument. If this organism is a tree then this organism is a plant this organism is a tree therefore this organism is a plant. Now that argument is deductively valid. It also happens to have all true premises and a true conclusion. Now having all true premises and a true conclusion is necessary or excuse me if the premises are true then the conclusion must be true right that that's true for a deductively valid argument but merely because you have all true premises and a true conclusion does not mean that the argument is valid right. So here's another argument if this organism is a tree this organism is a plant this organism is a plant therefore this organism is a tree okay all true premises and a true conclusion but that's not a deductively valid argument. That argument tries to make an inference from the consequent of a conditional which is necessary for the antecedent. Tries to make an inference from the consequent to the conditional to the antecedent which is a classical fallacy and logic called affirming the consequent. But that doesn't work. I'm going to show you why I will provide two true premises with the false conclusion that uses the same form. If this organism is a vine then this organism is a plant this organism is a plant therefore this organism is a vine. All premises are true right you might say wait wait the conditional has if this organism is a vine but that's a tree remember a conditional only asserts a truth relationship between the two component propositions from the antecedent to the sufficient and makes no claims as to whether the antecedent is true or the consequence is true or false. All this says is if the antecedent is true then the consequence is false and if this happened to be a vine then yes it would indeed be a plant so that conditional if this is a vine then this is a plant that's true. Remember our discussion with conditionals when we dealt with the truth conditions for a conditional a condition is false only if if and only if the antecedent is true and the consequence is false that's the only way you could demonstrate that a conditional is false is if the truth relationship is sufficiency does not actually hold but it does hold. If this is a vine then this is a plant so that first premise is true the second premise is also true this is a plant so both premises are true but the conclusion is false the conclusion states this is a vine this is not a vine this is a tree. So validity does not mean all true premises and a conclusion so we're not going to test for validity by going to our truth table and finding a row with all true premises and a conclusion that's not enough that's not enough all validity means is that there's a relationship if the premises are true then the conclusion must also be true so just to be clear right validity does not mean all true premises and a true conclusion right you can have all true premises and a true conclusion and the argument not be valid because the relationship does not hold okay so try to clear up one misconception right all validity means is that if the premises are true the conclusion must also be true that means it's impossible that you have all true premises and a false conclusion so one misconception is that you in fact have all true premises and a true conclusion therefore you have a valid argument that's not the case we already saw why it's also not the case that if you have false premises then you have an invalid argument that's not it so here's a deductively valid argument all right if this organism is a tree then this organism is Don Cheadle this organism is a tree therefore this organism is Don Cheadle deductively valid radically false premise right there's nothing about being a tree when it necessitates that the organism is Don Cheadle right just doesn't work it's a really really false premise however the argument is still deductively valid right because it has the right form and it's the conditional with the assertion of the antecedent and since the antecedent is sufficient for the consequent we may infer the consequent so all deductive validity claims is that if the premises are true then the conclusion must be true it has the right relationship it doesn't claim that all the premises are true and the conclusion is true that's not the claim it doesn't claim that all the premises are true right or that you know it doesn't claim that if the premises are false then it's then it's not valid that's not it at all all it's claiming so it doesn't matter whether the premises are in fact true or false all that matters is the relationship that's all that matters is the relationship all right so you might wonder well how are we going to understand this relationship how are we Are we even going to express it or comprehend it? Well, that's where the truth tables come in. Remember, at the truth tables, you get every possible truth assignment for the atomic propositions. And the truth assignments of the propositions, atomic propositions, gives us all the truth assignments for the complex propositions. Remember, the truth value of the propositions determines the truth value of the complex propositions. And if we get all those possible combinations, we can see every possible way that the complex propositions are true or false. And every possible way that the conclusion is true or false, given the truth assignments for those atomic propositions. So we will look at the argument on the truth table. Look at all the different ways that it's true or false, that the propositions are true or false. And we will try to find a right to the truth table. We will try to find a row where the conclusion is false and all the propositions are true, where the conclusion is false and all the propositions are true. If we can't find that row, if it doesn't have a row with all true premises and a false conclusion, the argument is valid. The argument is valid. If you find a row with all true premises and a false conclusion, it's invalid. That's the only way an argument is valid or invalid using the truth tables. Now, I could try to go through a rather lengthy explanation. I should try to go through several examples. But without something really to look at, it's probably not going to be that helpful. So the next video has more than a few practice exercises where I take you through step by step how we go through these problems, these sorts of problems that we're going to look at. Now, keep in mind there's a difference between a full truth table and abbreviated truth table. Learn the full truth table first. That will help you understand the abbreviated truth table. So once again, deductively valid. If the premises are true, the conclusion must be true. This doesn't necessitate that all the premises are true and the conclusion is true, just if the premises are true, the conclusion must be true. It also doesn't mean that if you have a false premise without the arguments invalid. No, it doesn't make the claim that all the premises are in fact true. It doesn't mean that if you have all true premises and a true conclusion, then it's no. Only if all the premises are true, then the conclusion must be true. And you verify this by putting it out on a truth table and seeing that there's a row where all the premises are true and the conclusion is false. If you find a row with all the premises are true and the conclusion is false, it's invalid. If you can't find such a row, it's valid.