Diagramming & Types of Reasoning - Logical Reasoning

[amagari]

I'm confused by the types of reasoning in logical reasoning questions.

1. Assuming I want to diagram every logical reasoning problem just so I can understand it, how do I determine what and when to diagram?

2. How do I know when it's conditional logic or what are the other types of logic and how could I diagram it?

For example, with must be true questions, can you always diagram these problems? Is there always one type of logic? I don't know how to get them right every time.

[Adam Tyson]

Hey there amagari, let's see if I can make your life a little easier here!

Unlike logic games, which are almost all about the diagram, most LR questions are NOT built to be diagrammed, and trying to do so would be difficult, time-consuming, and not at all helpful. In our process, we reserve diagramming for conditional reasoning questions (those based on "if...then" structures) and, sometimes, something called formal logic (which is a close cousin to conditional reasoning, but is less absolute - it's about things like "most A are B and some B are C"). Of the two, conditional reasoning is the more prevalent on the LSAT, but even then it is rarely found in more than 20% of the questions (roughly 10 questions per test). Sometimes a little more, sometimes a little less, but always a minority of the questions by a big margin.

How do you recognize it? By the use of conditional language. In our courses and books we talk about some of the most common indicators, although our lists are not by any means exhaustive. Words like "if", "when", "all", "every", and "in order to" indicate sufficient conditions, which are conditions that, when present, require the presence of something else. That something else is called the necessary condition, and that can often be found tied to words like "only", "then", "must", and some very special ones like "unless" and "without". Getting into all the details of how to recognize, diagram, and manipulate conditional logic is too much for one post here in the forum, but you'll find it discussed and explained at length in many of our publications and in many posts in this forum dealing with specific questions. When you encounter a conditional claim, like "if you jump in the pool, you will get wet", you diagram it like this:

Jump in Pool Get Wet

Many, but not all, Must Be True questions will indeed contain conditional language, and when that happens the correct answer could be based on a contrapositive of the original conditional claim (where the sufficient and necessary conditions get reversed and negated - Get Wet Jump in Pool) or on jumping over some link in a conditional chain (which is also known as making an additive inference). Again, these are discussed at length in our materials and courses.

Formal logic is typically diagrammed in a manner very similar to conditional language, with qualifiers like "most" and "some" added to the arrows, like this:

Puppies Cute

(Most puppies are cute)

So what about the other 80% or so of the LR questions? Don't diagram them. Don't even try. There is little to be gained and much to be lost in doing things like labeling premises and conclusions and trying to arrange them in some sort of pictogram. Instead, focus on understanding them structurally and determining whether they present an argument or not, and if so then what the conclusion is, and whether the argument is good or if it is flawed (and in what way it is flawed). No diagrams required, just analysis and understanding. Try paraphrasing the argument to make it easier to digest.

If you are in one of our courses and just getting started, all of this will become clearer as time goes on. At first, right after Lesson 2 on conditional reasoning, everything will look conditional to you! Over time, though, you'll begin to see when it is present and know when it is not, and what to do in either case.

Hang in there, be patient, and good luck!

[amagari]

I know you guys are against diagramming but I find it extremely helpful. For argument's sake, what if I wanted to diagram every single question on the exam, is that theoretically possible? Like all questions can be diagrammed in one manner or another?

Also how do you know which statements to diagram if there aren't any of the traditional indicator words?

[nicholaspavic]

I know you guys are against diagramming but I find it extremely helpful. For argument's sake, what if I wanted to diagram every single question on the exam, is that theoretically possible? Like all questions can be diagrammed in one manner or another?

Also how do you know which statements to diagram if there aren't any of the traditional indicator words?

Hi amagari,

Great questions. Certainly as Adam said, a lot of the stimuli will not lend themselves to diagramming (even though many students tend to see conditional diagramming everywhere at first in Lesson 2).

It's important to realize that diagramming is only one of the many tools you will have in your bag by the end of your LSAT studies. So there are a number of techniques to learn when successfully attacking any given stimulus and diagramming is only one. So to answer your theoretical question, the answer is no. There is sometimes little to no diagrammable logic in a stimuli. Moreover, attempting to diagram every question on a Logical Reasoning section would be an incredibly time-consuming task for the alloted 35 minutes, so I would strongly advise against it.

As far as knowing which statements to diagram when there are no traditional indicator words, as you go through the course or materials, you will become more comfortable with recognizing conditional or other formal logic in a stimulus. Practice makes perfect here and it is a skill that will develop with time. Reading for structure, argumentation and conclusions will allow you to eventually quickly recognize and distinguish between things like sufficient and necessary conditions. If you are early in your preparations, practicing them now will allow you to quickly identify them in the future without the time-consuming chore of making diagrams for everything that you have just read. But certainly for now, assuming you are at an early stage, try to focus as much as possible on using the Conditional Indicators identified in our lessons, drills and homework in order to progress rapidly and achieve a comfort level with them.

Thanks for your follow up!

[amagari]

Thanks for the info. Also how does formal logic fit into conditional logic? It seems sometimes they are referred to as essentially the same thing and other times they seem to be completely different.

[Francis O'Rourke]

Conditional Logic refers to statements that contain a notion of necessity or certainty. These statements provide guaranteed connections between two or more terms.

Formal logic is very similar to this, but includes less-than-certain terms, such as "some," "most," "usually," "not all," etc...

Everything that you learned about diagramming conditional logic can be applied to formal logic, but make sure to take a lot of care with making connections between terms in chain relationships and taking the contrapositives of formal logic statements (there is no contrapositive when a formal logic statement uses the term "some" or "most".