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Types of Deductive and Inductive Arguments

Types of Deductive and Inductive Arguments

Author: Glenn Kuehn
Description:

In this lesson, students will learn about different types of deductive and inductive arguments.

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Source: Image of Socrates, Creative Commons, http://bit.ly/29ZntMM

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Hi, I'm Glenn. And this is the ethics tutorial on the types of deductive and inductive arguments. First, let's look at a couple of ideas to keep in mind and then cover the content of the tutorial.

In this tutorial, we will cover types of deductive argument, types of inductive arguments, each with examples, and then we will practice identifying these types with further examples. In the category of deductive arguments, there are five that we'll address. I'll first list them, and then I'll define them and provide examples. We have argument from definition, categorical argument, hypothetical argument, disjunctive argument, and the argument from mathematics. An argument from definition is one where the conclusion follows from premises based solely on the meaning of the words that are used.

So for example, we have all squares have four straight sides. All straight-sided figures with four sides are quadrilaterals. Therefore, all squares are quadrilaterals. This conclusion is established simply because of the words that are used and their definitions.

The categorical argument is one where the conclusion follows from the premises based on the categories that are used. That is where we look for words like all, some, none, only-- words like that.

So for example, all dogs are mammals. Willow is a dog. Therefore, willow is a mammal. This conclusion is established because of the categories that are referenced.

Hypothetical argument-- this is where the conclusion follows from the premises based upon the use of an if-then statement. Usually, it's explicit, but sometimes it's implicit. We look for the conditional statement.

For example, if it rains, we won't go running. It is raining. Therefore, we won't go running. The conclusion is established based upon the condition of raining and determine we won't go running because of that.

A disjunctive argument is one where the conclusion follows from the premises based upon the use of an either/or statement. For example, Ted's major is either music or biology. Ted's major is not music. Therefore, Ted's major is biology. We look for one-or-the-other either/or scenario.

And finally, the argument for mathematics is one where the conclusion follows from premises based upon the meaning of mathematical terms and concepts. Example, all even numbers are divisible by 2. 56 is an even number. Therefore, 56 is divisible by 2. Given the definitions of mathematical terms, the conclusion is established.

We can see then that the commonalities of deductive arguments are the following. The conclusions are always 100% certain given the structure of the argument. The conclusions are based upon the meaning of the words and the form of the argument. And the conclusion is not based upon the truth and the falsity of the premises.

In the category of inductive arguments there are six that we'll look at-- causal inference, prediction, generalization, argument from authority, argument from signs, and analogy. A causal inference is one where the conclusion follows from the premises based upon inferring a cause-and-effect relationship. For example, I hear the sound of piano music, so I infer that someone is playing the piano. There is a causal relationship operating here.

Second is prediction. This is where the conclusion follows from the premises based upon inferring that the present or the future will resemble the past. It has rained every day for the past week. Therefore, it's probably going to rain tomorrow. Given what has happened, I can predict with reasonable certainty, though not 100%, that it will continue.

A generalization is a conclusion that follows from the premises based upon inferring a sample to a larger population or inferring a larger population to a sample. You can go either way. For example, most professional basketball players are tall. Mark is a basketball player. Mark is probably tall. Given the group, we can infer something about the individual.

An argument from authority is where the conclusion follows from the premises based upon an assumed truth or accuracy of the claims of an expert. Steve is a sports analyst. Steve says that the Packers will be unstoppable this season. Therefore, the Packers will most likely be in the playoffs. Given Steve's authority as a respected analyst, we can take his word.

An argument from signs is where the conclusion follows from the premises based upon an assumed truth or accuracy of an intended communication but not from expertise. So we look at signs, indications.

John has a fever. John keeps coughing. Therefore, John must be sick. He's showing symptoms of being sick. These are the signs.

And then finally is an argument from analogy. This is where the conclusion follows from the premises based upon inferring a further similarity from what is known already. So we could use something like, life is a book. Every day is a new page. Every month is a new chapter.

This argument is slightly reversed in its premises and conclusion. The conclusion is, life is like a book. And that's because every day is a new page, and every month is a new chapter. There is an analogy being made.

So we can see a couple of commonalities on inductive arguments. First, the intended conclusion is based on what is known. And then we make a prediction based upon that. And the conclusions are always more or less probable. They are not 100% certain.

Let's look at a couple of examples of arguments and try and determine whether or not they are inductive or deductive. I'll give you a hint. Two are inductive, and two are deductive.

First, actors tend to be extraverts. Tom is an actor. So Tom is likely an extravert.

An indication that this is inductive is the use of the word likely in the conclusion, which shows that it's probable. So it's inductive. And it is going from a general statement about actors to a specific statement about Tom, so it's a generalization.

Second, all actors are extraverts. Tom is an actor. So Tom is an extravert.

This presents a conclusion that is certain, given the premises. So it is deductive. And given the use of the word all, it is a categorical argument.

It is cloudy outside. The barometer has a low reading. It is probably going to rain today.

We see the word probably. That indicates a conclusion that is not certain, so it's inductive. And we're looking at indications of weather conditions, which are signs. So it's an argument of sign.

And finally, either it's going to rain today or it isn't. It's not the case that it isn't raining. Therefore, it's raining.

In this tutorial, we have looked at the types of deductive and inductive arguments, seen five types of deductive arguments, six inductive arguments, and then practiced identifying the differences between them.

Notes on “Types of Deductive and Inductive Arguments”

(00:00 – 00:26) Introduction

(00:27 – 00:42) Content of Tutorial

(00:43 – 03:44) Types of Deductive Arguments

(03:45 – 07:05) Types of Inductive Arguments

(07:06 – 08:30) Argument Identification

(08:31 – 09:00) Summary