What Is a Propositional Statement?

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In logic and philosophy, a propositional statement is a sentence or expression that is either true or false. Generally speaking, a statement is propositional because it makes a proposition about the world; that is, it asserts a truth. This doesn’t mean the statement is true but only that it contains an assertion of some kind. Even saying something as simple as “the sky is blue” is a propositional statement, because it's assuming a logical connection between the sky and the color blue.

Understanding Truth Value

According to the computer science department at the University of Texas, Austin, the truth value of a propositional statement can be either true or false depending on the logical validity of the statement. For example, the statement “all dogs are cats” contains a general assertion about dogs that is logically inconsistent: Dogs cannot be both dogs and cats at the same time. The truth value of this statement, then, would be false. A propositional statement that is always true is called a tautology, while a propositional statement that is always false is called a contradiction. For instance, the statement “I will eat my dinner or I will not” is a tautology, because it allows for either instance and therefore is always true.


About the Author

Scott Neuffer is an award-winning journalist and writer who lives in Nevada. He holds a bachelor's degree in English and spent five years as an education and business reporter for Sierra Nevada Media Group. His first collection of short stories, "Scars of the New Order," was published in 2014.

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