Before you begin reviewing all the material in this unit, let’s reflect on the main topic: logic. Please, share your opinion about logic in the poll below.
This unit serves as a refresher for those who studied logic previously and a crash course for those who had not.
As a reminder, all the materials listed here are required to complete the unit. Supplemental materials are collected at the bottom of the page under the Supplemental Resources. Some terms are highlighted and hyperlinked to their definitions in our glossary. If you see an unfamiliar terms and it is not highlighted, I encourage you to research it and submit its definition using the form here. The term will be added to our glossary with a “submitted by” note.
Be sure to check the Blackboard course website for all activities and assignments in this unit.
What is logic?
How to Argue – Philosophical Reasoning (Crash Course Philosophy)
Before we dive into the big questions of philosophy, you need to know how to argue properly. We’ll start with an overview of philosophical reasoning and brea…
Put simply, the study of logic is the study of proper reasoning.
You might be thinking “but all human beings are able to reason — it is one of our basic abilities.”
While it is true that we all are able to reason, what is also true is that at times, our reasoning is faulty. Sometimes, we do not consider all the facts or do not consider them properly, sometimes we might miss important connections, sometimes we might ignore certain questions that we should have asked, and sometimes we are swayed by our emotions.
Studying logic can help us avoid some of the more common reasoning mistakes, which would benefit us both in the professional and personal spheres of our lives.
Logic, as a study, can be formal or informal. Informal logic deals with reasoning as it occurs in our daily lives, while formal logic is concerned with examining rules and patterns of reasoning, often using a symbolic language to do so. In this course, we are concerned with informal logic. To learn more about it, take a look at the Informal Logic page on the Stanford Encyclopedia of Philosophy website, which also happens to be one of our supplemental resources in this unit.
The basic components of logic are propositions. These are sentences that express facts and, therefore, have the capacity to be either true or false. So, sentences like commands or questions are not considered to be propositions because they are not informative (do not communicate facts) and cannot be determined to be true or false.
Van Cleave, M. (2019). 1.1: What is an Argument? In Introduction to Logic and Critical Thinking [OER text]. Retrieved from https://human.libretexts.org/Bookshelves/Philosophy/Introduction_to_Logic_and_Critical_Thinking_(van_Cleave)/01%3A_Reconstructing_and_Analyzing_Arguments/1.01%3A_What_is_an_Argument
Both logic and critical thinking centrally involve the analysis and assessment of arguments. “Argument” is a word that has multiple distinct meanings, so it is important to be clear from the start about the sense of the word that is relevant to the study of logic. In one sense of the word, an argument is a heated exchange of differing views as in the following:
Sally: Abortion is morally wrong and those who think otherwise are seeking to justify murder!
Bob: Abortion is not morally wrong and those who think so are right-wing bigots who are seeking to impose their narrow-minded views on all the rest of us!
Sally and Bob are having an argument in this exchange. That is, they are each expressing conflicting views in a heated manner. However, that is not the sense of “argument” with which logic is concerned. Logic concerns a different sense of the word “argument.” When we use the word “argument” in logic, what we have in mind is a reason or a set of reasons for why some claim or idea (i.e. proposition) is true.
Sally: Abortion is morally wrong because it is wrong to take the life of an innocent human being, and a fetus is an innocent human being.
In this example Sally has given an argument against the moral permissibility of abortion. That is, she has given us a reason for thinking that abortion is morally wrong. Sally’s claim is the proposition “abortion is morally wrong.” The reasons she provides are seen as evidence for the truth of the claim she is making.
The claim — the proposition for which reasons are being provided in an argument — is called “conclusion“. The reasons or evidence are called “premises“.
Thus, in logic, an argument is simply a collection of propositions, one of which is the conclusion and the others premises.
Van Cleave, M. (2019). 1.2: Identifying Arguments In Introduction to Logic and Critical Thinking [OER text]. Retrieved from https://human.libretexts.org/Bookshelves/Philosophy/Introduction_to_Logic_and_Critical_Thinking_(van_Cleave)/01%3A_Reconstructing_and_Analyzing_Arguments/1.01%3A_What_is_an_Argument
Most arguments we encounter are presented informally, meaning that the different parts of the arguments are not clearly identified. Often, in order to be able to understand, evaluate, and refute an argument we need to reconstruct it using standard argument form.
This sentence represents an informal argument that can be resented formally in the following way:
Hermanus Backpackers, CC BY 2.0 , via Wikimedia Commons
Premise 1: All fish have gills.
Premise 2: Sharks are fish.
Conclusion: Sharks have gills.
In the standard argument form, premises are separated from the conclusion as well as from each other. Each proposition is stated separately as a complete sentence and starts on a new line. If premises and conclusion are not labeled, typically, the last statement in the set will be the conclusion. Sometimes, a horizontal line will be drawn separating the premises from the conclusion.
But how can we tell that a passage we are reading (or hearing) is an argument? The best way to identify whether an argument is present is to ask whether there is a statement that someone is trying to establish as true by basing it on some other statement. If so, then there is an argument present. If not, then there isn’t.
Another thing that can help in identifying arguments is knowing certain keywords or phrases that are premise indicators or conclusion indicators.
Premise indicators: because, since, for the reason that. Conclusion indicators: therefore, then, so.
Although these words and phrases can be used to identify the premises and conclusions of arguments, they are not failsafe methods of doing so. Just because a sentence contains them does not mean that you are dealing with an argument. The more you practice the more you would be able to figure out whether something is an argument or not.
Consider some examples below. Some are arguments and some are not, even though they have indicator words or phrases.
Examples
Susy was carrying a tray of marbles when she tripped, thus spilling the marbles all over the floor. — No argument is being presented here.
Do not give Steve that cookie because he is allergic to peanuts. — No argument is being presented here.
Billy broke my nightlight because he was the only person who visited my room yesterday and I did not break my own nightlight. — An argument is being presented here with the conclusion “Billy broke my nightlight”.
Test your understanding
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Types of arguments
Most of the following has been adapted from:
Van Cleave, M. (2019). 1.8: Deductive vs. Inductive Arguments In Introduction to Logic and Critical Thinking [OER text]. Retrieved from https://human.libretexts.org/Bookshelves/Philosophy/Introduction_to_Logic_and_Critical_Thinking_(van_Cleave)/01%3A_Reconstructing_and_Analyzing_Arguments/1.01%3A_What_is_an_Argument
The types of argument reflect the different kinds of reasoning involved. The two most common types of arguments and the ones we will focus on are deductive and inductive arguments.
A deductive argument resembles an equation of arithmetic in that it is straightforward and can only lead to one solution (i.e. conclusion). The kind of relationship that exists between the premises and the conclusion of a deductive argument is one where the conclusion is guaranteed by the premises if the argument is proper.
In contrast, an inductive argument does not have a guaranteed conclusion. The nature of the relationship between the premises and the conclusion is such that the premises make the conclusion likely or probable, but never certain. Inductive reasoning is generally used to make predictions, support assumptions, establish theories, and generally advance knowledge by taking a logical leap from.
While all arguments can be proper or improper, good or bad, since the kind of reasoning that is involved in these two types of arguments is very different, we use different criteria to evaluate the two types of arguments.
A good deductive argument must have proper form. That is, the conclusion should be derivable from the premises. This is the first criterion used to evaluate deductive arguments and it is called validity. A valid deductive argument is an argument whose conclusion cannot possibly be false, assuming that the premises are true. Another way of putting this is as a conditional statement: A valid argument is an argument in which if the premises are true, the conclusion must be true. Consider the valid deductive argument below:
1. Violet is a dog.
2. All dogs are mammals.
3. Therefore, Violet is a mammal.
You might wonder whether it is true that Violet is a dog (maybe she’s a lizard or a buffalo—we have no way of knowing from the information given). But, for the purposes of validity, it doesn’t matter whether premise 1 is actually true or false. All that matters for validity is whether the conclusion follows from the premise. This argument is clearly valid since if we assume that “Violet is a dog” is true, then, since all dogs are mammals, it follows that “Violet is a mammal” must also be true. As we’ve just seen, whether or not an argument is valid has nothing to do with whether the premises of the argument are actually true or not.
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