“What is logic and what is it good for?”: Reasons to Study Logic—Part 1


1. Order. You may be wondering, “What can I do with logic?” The answer is that logic can do something with you. Logic builds the mental habit of thinking in an orderly way. A course in logic will do this for you even if you forget every detail in it (which you won’t, by the way), just as learning Latin will make you more habitually aware of the structure of language even if you forget every particular Latin word and rule.

No course is more practical than logic, for no matter what you are thinking about, you are thinking, and logic orders and clarifies your thinking. No matter what your thought’s content, it will be clearer when it has a logical form. The principles of thinking logically can be applied to all thinking and to every field.

Logic studies the forms or structures of thought. Thought has form and structure too, just as the material universe does. Thought is not like a blank screen, that receives its form only from the world that appears on it, as a movie screen receives a movie.  A study of logic will show you the basic forms (structures) and the basic laws (rules) of thought, just a a course in physics or chemistry shows you the basic forms and laws of matter. [Adapted from Peter Kreeft, Socratic Logic]

Categories : logic


  1. Shannon Henry says:

    I understand the need for logic and value its use. However, I’m unsure how some of the things they are learning in logic, such as truth tables, are of any practical use. What do our students gain from truth tables?

  2. RBradley says:

    Truth tables are practically useful in a number of ways. I’ll discuss just two.

    It is important to note that truth tables are unique to propositional logic, one system of logic among a much broader class of other distinct logical systems that do not use truth tables. So, when making a judgement about the usefulness of truth tables, we need to make sure we understand their function first, and only then can we judge their usefulness or uselessness. Though limited in scope, they have a very important function within this one logical system: namely, they provide a visible scheme that clearly illustrates the truth-functional nature of propositional logic. This may not mean much to you now, but if I wanted to show you what these truth-functional relationships were, I would need to use nothing more than a truth table to demonstrate this relationship to you. In short, truth tables are pedagogically useful.

    Secondly, truth tables can be used to test for the validity of a propositional argument. Testing for validity is a necessary task in logic. We want to be able to distinguish between good and bad reasoning, and testing for validity is the first step in that process. Truth tables provide us with a sound method for testing certain arguments for validity. While students are learning propositional logic, one skill they must master is that of taking an argument written in English—one they might encounter in a real-life situation—translate it into a prescribed logical language that better reveals its logical structure, then test that argument using the truth table method.

    Truth tables can be used in real life; yet, they are limited by their specific application to one branch of logic. But this should not in any way count against its usefulness. After all, the Cartesian plane is extremely useful in situations where it applies, and by this fact we say it is a useful tool. But where it doesn’t apply, it will not be useful. In other words, its good at what it does. The same is true of truth tables.

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