Line of Reasoning

Get ready for the enthymeme. It works better than it spells.

What is reasoning? And why is it a line and not, you know, a circle? (Actually, circular reasoning is a thing. Technically, an illogical thing.)

First, reasoning. It means using logic to prove or disprove a claim. In formal logic, classical reasoning employs the syllogism.

 All men are mortal.

Socrates is a man.

Therefore, Socrates is mortal.

The philosopher Aristotle, who wrote the greatest book on rhetoric, realized most mortals just don’t talk this way. Everyone knew that Socrates was a man, or at least he identified as a man. So Aristotle threw out the middle part of the syllogism. Thus he created the enthymeme (EN-the-meem), the one-two logic punch. 

Now, you may or may not be taught the term. But it’s a good concept to know, because it will help you follow the line of reasoning in any reading you’re assigned. Plus it will make you more logical in your own writing. The line of reason lies at the very hard of argument—and of AP Lang. 

The enthymeme works like this:

Premise, therefore conclusion.

 Dogs are more loyal than cats, so you should get a dog instead of a cat.

 What’s the premise? Dogs are more loyal than cats.

What’s the conclusion? You should choose a cat over a dog. 

That’s the line of reasoning. It’s a line because the premise leads directly to the conclusion. Of course, the validity of the conclusion depends on the rhetor’s understanding of the audience. If it values loyalty above anything else in a pet, then this makes for a persuasive logical argument. (Jay, on the other  hand, loves cats because they’re rhetorically more interesting. A dog just says yes to everything.) 

That reasoning-line can go in either direction; you can start off with either the premise or the conclusion.

Conclusion first: You definitely should get a dog. It’s much more loyal than a cat.

Premise first: Dogs are more loyal, so you should get a dog.

When you put the conclusion first, you’re using deductive reasoning. It states a proposition—something the rhetor wants you to believe or choose, or to act on—and then defends that logic with one or more reasons. 

[Conclusion:] Our nation needs immigrants to energize our economy. [Premise:] It’s immigrants who built our entrepreneurial economy in the first place.

 That’s deductive reasoning. Now try putting the premise first. 

[Premise:] Immigrants made America the entrepreneurial nation it is today. [Conclusion:] We need immigrants to continue making us the world’s entrepreneurial leader.

When you put your premise first, you’re using inductive reasoning. 

Why should you care about the difference? Generally, deductive reasoning is easier for the reader to process. She sees where you’re coming from, right from the get-go. Here’s what you believe, and here’s why you should. Inductive reasoning, on the other hand, often makes for better storytelling. You don’t have to stick to one premise; you can use a number of them, along with facts and anecdotes (see Claims & Evidence. The reader follows along, ideally becoming convinced before you even tell her what to think.

Deductive reasoning:

Definitely get a dog. How many cats run to the door when you come home, unless it’s for food? Or try getting a cat to go on a walk with you. A dog thinks a walk is the very best moment of its day. A dog will follow you anywhere. It will pull you out of a house fire, defend you from attack, and think you’re the most wonderful creature in the world. A cat? It’s always looking out for number one. Dogs are loyal. Cats are selfish.

Inductive reasoning:

Think what it’s like to have a cat. You come home and have to search your apartment to find where it’s napping. You wake it up, and it starts meowing at you, like, Feed me. Offer to take it for a walk, and it looks at you like you’re crazy. A dog, on the other hand, will greet you joyfully. It will run and get its leash. And if anything goes wrong—a fire, or an intruder—a dog will defend you to the death. A cat? It will hide under the bed while wondering if the intruder has any food.

Both kinds of reasoning follow a line—or, you might say, a path. The more formal your argument, the straighter that path should be. Your premise (or premises) should lead directly to the conclusion—or follow it clearly.

Contents