About this video
A logical-reasoning lesson that compares the argument structure of a Patricia example against five answer choices. The instructor maps the chain of conditions (heavy spicy meal leads to heartburn, which leads to a grouchy morning), then tests each option by asking whether it follows the same forward chain of if-then reasoning, which only one choice does.
You'll be able to
- map an argument as a chain of if-then conditions.
- tell a forward conditional chain from reasoning that starts at an outcome and works backward.
- match an argument to the answer choice that has the same logical structure.
Key words
- Logical structure
- The pattern of how an argument's claims connect, regardless of its subject matter.
- Conditional chain
- A series of if-then statements in which one condition leads to the next and finally to a conclusion.
- Forward reasoning
- Starting from the first condition in a chain and concluding its end result.
- Either-or structure
- A claim that one of two options is true, which leads to a different kind of conclusion from a chain.
- Denying the consequent
- Concluding that an earlier step did not happen because a later outcome did not occur.
Transcript
- [Instructor] If Patricia eats a heavy, spicy meal tonight, she will get a bad case of heartburn later. If Patricia gets a bad case of heartburn later, she will be grouchy tomorrow morning. So if Patricia eats a heavy, spicy meal tonight, she will be grouchy tomorrow morning.
Which of the following arguments is most similar in its logical features to the argument above? So, before I even look at these choices, let me map out what's going on over here. So, they say if Patricia eats a heavy, spicy meal, she will get a bad case of heartburn later.
So, let me write heavy, heavy, spicy meal leads to heartburn later. Heartburn later. And then it says if Patricia gets a bad case of heartburn later, she will be grouchy tomorrow morning. So, that's going to lead to being grouchy tomorrow morning. Grouchy morning.
She's going to be grouchy tomorrow morning. So, if Patricia eats a heavy, spicy meal today, tonight, she will be grouchy tomorrow morning. So, they're saying that last statement if this first thing happens, it's going to lead to this thing, and so you're going to get a grouchy morning.
Alright, so let's see which of these choices have a similar, similar logical features. Alright, so this first one. If Ruth plants only daffodils, the squirrels will eat the bulbs. So, only, only daffodils. Daffodils. So, let me see. Plants. Only daffodils, and the squirrels will eat the bulbs.
Squirrels eat bulbs. (laughs) Alright. If the squirrels eat the bulbs, then no flowers will bloom in Ruth's garden. So, no flowers bloom. No flowers bloom. Since no flowers are blooming in Ruth's gardens, in Ruth's garden, she must have planted only the daffodils.
Alright, so let's... So, this, like the first example, it sets up this logical chain. But in the first one, we set up the logical chain; and then we said if this happens, then that has happened. So, if this the beginning of our logical chain, then we get to the conclusion on it.
But this one goes the other way around. It says since no flowers are blooming. So it's saying since this, since this, they're concluding somehow that she must've only planted daffodils. Then this. So, it's definitely not the same logical structure as the first example.
So, let's rule out this first choice. So, now let me go to choice B here. Let me scroll down. There're several other choices here. So, B through E are here. So, this next one. It says if Shawn starts gardening in early spring, he can plant tomatoes early. So, I'll say gardening early.
Gardening early spring. Early spring. If he does that, he can plant tomatoes early. So, plant. Can plant. Tomatoes. Tomatoes. Early. If Shawn can plant tomatoes early, he will have plenty of tomatoes for canning. Plenty for canning. Alright, that makes reasonable.
That sounds reasonable. But he does not have plenty of tomatoes for canning. So, not this. So he either did not start gardening in early spring or he did not make, plant tomatoes early. So, whether or not this is a logically valid conclusion, it's doing it structurally different.
He's saying, "Okay, look, this isn't there; "so therefore, one of these other "things must not of happened." But that's not the same logical structure as our first example. Remember, our first example we set up this logical chain, and then we say, "Hey, look, if Patricia does this, "then this thing will naturally happen."
The end of our logical chain. B also does not do that. So, let's keep going. Let's go to C, and actually, let me clear out some space here so that we can do that right next to. So, we delete that. So, now let's look at choice C here. I'll do that in orange. Maria plants either petunias or geraniums in her garden.
So, petunias. She does either petunias or geraniums. This is already looking different. Geraniums. In her garden. If she plants petunias, she plants purple ones. Plants purple ones. This one just has a completely different structure. Purple ones. If she plants geraniums, she plants red ones.
Plants red ones. Since both petunias and geraniums are flower, Maria will have either purple or red flowers in her garden. So, this is a completely different logical structure. They set up this option she's either going to do either of these things. And then if she does either one of them, then what happens.
And then they make a different type of a conclusion. So, once again, we're not trying to say is she making, are we making a valid statement or valid conclusion? We're saying is it a similar logical structure? And this was clearly a different logical structure than the passage that starts off this question.
So, now we're left with D and E. So, let's see, choice D. If Li plants old rose varieties. So, plants old rose varieties. Her garden will look beautiful. So, beautiful. Beautiful garden. If Li's garden looks beautiful, Li's neighbors will be impressed. So, this leads to impressed neighbors.
Impressed neighbors. So if Li plants old rose varieties, her neighbors will be impressed. So, if this happens, then this will happen. And not only does that make sense if you follow, if all of these logical statements are right because if this happens, then this is gonna happen, and if that happens, then this is gonna happen.
But it's also the exact same structure that we saw in our original passage. They set up this logical chain, and they said, "Okay if the beginning "of the logical chain happens, "then we can conclude the end of the logical chain." And that is the exact same structure that is happening in choice D here.
So, I definitely like choice D. But just for good measure, let's look, take a look at choice E. And to feel good that that is a different logical structure, or a different type of a chain of logic. So, let's see. It says if Bryan's fruit trees are to produce well, he must either prune them...
Okay, so, so if you want to produce well. This already looks different. If you want to produce well, he must either prune them in the fall or fertilize them in the spring. So, prune or fertilize. This is actually the logical. If he does one of these, then he'll make them produce well.
Fertilize, so even, even in how the logical structure's being set up. Before we even try to make a conclusion, this already has a different shape. So, I would rule this out pretty quickly.
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