A formal logic class or textbook should teach us ways to know when an argument has a valid argument form, and that can take a significant amount of time to learn. I encourage everyone to learn formal logic one way or another because it is of central significance to rational argumentation, and it is not something we spontaneously understand instinctively or through personal experience. Perhaps the first philosopher to understand formal logic and the importance of validity was Aristotle, and philosophers would have liked to understand it sooner. It was a great achievement because it can be so difficult to figure out on our own. Even so, we can learn a lot about valid argument form very quickly. I will explain why we need to make sure our deductive arguments are valid, give examples of valid argument forms, and explain how we can improve our arguments. (more…)
May 13, 2013
May 5, 2013
The problem of evil refers to the fact that certain traditional views of theism involve contradictory beliefs. The problem is that God should be willing and able to make sure evil doesn’t exist, but evil exists. Some theists argue that atheists can’t reject the existence of God based on the problem of evil because atheists would then have to assume objective morality exists, but objective morality requires God. I will argue that the theist’s argument is irrelevant in consideration of one argument against one type of traditional theism, but it is somewhat relevant against another. Even so, both arguments are unsound. (more…)
May 2, 2013
April 19, 2013
Many people think philosophers aren’t experts, that we can’t really know anything about philosophical issues, or that everyone’s opinion is equal concerning philosophical issues. Philosophical issues are often narrowly understood to be those concerned with the nature of reasoning, knowledge, morality, or reality; and many people say we can’t know anything about such issues. I will argue that we can know something about philosophical issues, which implies that there can be expert philosophers, and that not everyone’s philosophical opinion is equal. We do seem to know something about philosophical domains and it is plausible to think we can give meaningful philosophical arguments within these domains. Such a position is actually more consistent with how people think about the world.
I will introduce the plausible view that we can know about scientific issues, and the common view that many people have that we can’t know about philosophical issues. I will explain why we can’t reject philosophy without being inconsistent, and I will give examples of various plausible philosophical beliefs and reasonable philosophical arguments. (more…)
March 21, 2013
Some of my key blog posts about propositional logic have been organized a free ebook. This ebook can greatly help people understand the importance of logically valid arguments and better understand logical form.
The focus of this book is propositional logic. I discuss the meaning of “logic,” the importance of logic, logical connectives, truth tables, natural deduction, and rules of inference.
March 6, 2013
Recommended reading: What is Logic?
Why is logic education important? The main question here is what the real point of logic education is. The real point of logic is not to teach people how to be logic professors, or to increase test scores, or to impress potential employers. Philosophers and mathematicians were very interested in understanding logic long before it was taught in universities precisely because of how important it is. Why is logic so important? The answer is that logic helps us better understand good arguments—it helps us differentiate between good and bad reasons to believe something. We should want to have well-justified beliefs. We want to know what we should believe. Understanding good argumentation helps us understand when we should believe something, and understanding logic helps us understand good argumentation. (more…)
February 20, 2013
This is part 6 of a series. Links to the other parts of the series are above.
The straightforward way to construct proofs using natural deduction is called the “direct method.” Every line of that type of proof is validly deduced from the premises and rules of inference. Every line of such a proof could be considered to be true as long as we consider the premises to be true. However, there are two other strategies: The conditional proof and the indirect proof. Both of these types of proofs introduce an additional premise that is assumed to be true “for the sake of argument.” (more…)
February 19, 2013
This is part 5 in a series. There are links to the other parts of the series above.
Natural deduction is used to give proofs of validity by showing all the steps in reasoning required. In this case natural deduction uses rules of inference to allow us to reach conclusions from statements of propositional logic. (more…)
February 12, 2013
At some point you are likely to hear about how giving arguments is rude and we would all get along better without arguing. Arguing is often thought to be a shouting match or hostile disagreement of some sort. However, argumentation is central to thinking rationally and critical thinking. The success of natural science could not exist without it. Yes, some arguments are disrespectful, but not all of them are. (more…)
January 29, 2013
January 22, 2013
It can be difficult to find anyone willing and able to engage in rational debate, but it is something I think we should aspire to having. Many people refuse to engage in rational debate because they find it offensive or they would rather engage in name calling. I believe that rational debate has a lot to offer. It can help us better understand how to reason properly and to develop critical thinking skills. Rational debate is important to everyone who wants to know what they should believe about a controversial issue because we need to know if there’s a good argument in favor of a belief. (more…)
January 19, 2013
Truth tables are an important tool for evaluating statements and arguments. We can create our own truth tables using following steps:
Translate statements of ordinary language.
Break all complex statements into smaller parts.
Determine how many columns are required.
Determine how many rows are required.
Determine the truth values of statement letters.
Determine the truth values of complex statements.
I will illustrate how to follow these steps by using an example. In particular, I will show how we can make a truth table of an argument to find out if the argument is logically valid. (more…)
January 14, 2013
Truth tables are visual aids to help us determine all the truth value possibilities of various statements. Learning about truth tables can help us better understand logic. Truth tables are used to define logical connectives, and to help us identify various distinctions (such as tautologies, self-contradictions, consistent statements, equivalent statements, and valid arguments).
January 8, 2013
December 31, 2012
You can download a PDF ebook of this introduction to argument mapping here:
Argument maps are visual representations of arguments to help people better understand them. A meta-analysis of various studies found that classes with lots of argument map practice are the most effective type of critical thinking class to help improve critical thinking skills. (more…)
December 6, 2012
I believe that argument maps as I understand them are superior to other types of argument diagrams. I will describe four different kinds of argument diagrams, then explain why argument maps seem to be the best. (more…)
October 22, 2012
‘Translation’ refers to the act of converting statements of natural language to statements of a symbolic logical system. In this case I will discuss how to convert statements of English into statements of propositional logic. Translation requires us to know logical connectives used in propositional logic, and ways we use logical connectives in English. (more…)
I have briefly discussed the meaning of “logic” and various parts of logic. I am now going to discuss the most important parts of propositional logic in greater detail. This will include the following chapters: (more…)
October 10, 2012
Logic is a domain of philosophy concerned with rational criteria that applies to argumentation. Logic includes a study of argumentation within natural language, consistent reasoning, valid argumentation, and errors in reasoning. It is divided into two main domains: Formal and informal logic. (more…)
October 3, 2012
I made two images concerning creationist arguments and I will explain why these arguments fail in greater detail below.