How to Evaluate the Reasoning in a Statement

Instructor: Richard Pierre

Richard has a doctorate in Comparative Literature and has taught Comparative Literature, English, and German

Understanding the reasoning and argumentation of a statement is key to evaluating its truth. This lesson will explain the steps required to analyze written statements, as well as how to identify common logical fallacies that make statements false.

Formal Logic

Whether analyzing a text for a class or just trying to understand the latest claim by a politician, there are times when you'll want to really evaluate a statement, and not simply decide whether or not you personally agree with it. The systematic study of arguments is known as logic.

Venn Diagram

It's a huge field, divided into two broad groups. Formal logic studies the form of arguments rather than the content of statements. It's something like ''If A equals B and B equals C, then A equals C.''

Often called symbolic logic, formal logic is really a branch of mathematics; you can turn the previous example into a series of equations: ''(4 + 3) = (1 + 6), and (1 +6) = (5 + 2), so (4 +3) = (5 + 2)''.

However, the study of argument forms doesn't necessarily tell you about the real-world truth of a statement (truth as we commonly see it). In other words, an argument can have a valid form yet be meaningless. The argument ''If all spiders are frogs, and all frogs are zebras, then all spiders are zebras'' has a valid form (it's the same as the examples above), but its content is bonkers.

Informal Logic

The second type, informal logic (often called critical thinking), allows us to evaluate statements as they apply to real-world contexts. Let's identify some key features of a good argument based on informal logic. Just remember that ''good'' here doesn't mean that a statement is a great idea, only that it is written in such a way that we can analyze it using informal logic.

An argumentative statement will show some degree of complexity. For example: ''We should educate our youth because this will lead to a more knowledgeable society.'' Whether or not we agree with this statement, it connects claims in a sensible way: educating the public leads to a knowledgeable society, and a knowledgeable society is a good thing. Since an argument contains a judgment of value, it also differs from a fact, which summarizes a condition that either is or is not true, like ''basic education is compulsory in the United States.'' In our example, the value judgment is the implicit claim that a more knowledgeable society is a good thing. An argument is not merely opinion, or a statement of belief or feeling that is not necessarily based on evidence, like ''I don't think education beyond the 9th grade is necessary.'' An argument is also understandable within a real world context. In our example, we can relate to concepts like ''education'' and ''society,'' and seek evidence for its claim about the value of education, such as by doing long-term sociological studies that track populations and their knowledge.

Logical Fallacies

Unfortunately, not all statements follow the standards of logic. We call these flawed statements logical fallacies. If you see that a statement contains a fallacy, it means that it's logically invalid--whether or not you agree with it, and even if part of it seems true. Here are just a few common fallacies:

Begging the Question

This fallacy, sometimes called circular logic, shows up in statements that make incomplete claims. Look at this statement, for instance: ''Lowering the legal drinking age is a terrible idea because people shouldn't be drinking at a younger age.'' Both parts of this statement speak against a lower drinking age without ever providing evidence or a supplementary claim to explain the reason why.

Slippery Slope

Also called the snowball effect, this fallacy assumes that just because something happened, it will continue to happen, usually with disastrous results. For example: ''In the last year alone, we've lost 100 jobs. If things keep going this way, in five years we won't have any jobs at all.'' In reality, the loss of 100 jobs might have been a fluke. Perhaps one large company shut down last year, and who knows--maybe next year we'll grow 300 more jobs.

Slippery Slope

''Ad Hominem''

This fallacy (Latin phrase for ''against the person'') makes an assertion about a person that is irrelevant in the context, whether or not it's true. Say you see a political attack advertisement that says ''Mrs. Smith shouldn't be our governor. She doesn't even drive an American car!'' It may or may not be true that Mrs. Smith drives a foreign car. However, the car a person drives isn't relevant to the duties of the office of governor. The assertion is just an emotional appeal against Mrs. Smith's character.

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