Part I: Terms and Definitions
• A statement is any unambiguous declarative sentence about a fact (or non-fact) about the world. It says that something is (or isn’t) the case. • An argument is a series of statements meant to establish a claim. • A claim or conclusion is the statement whose truth an argument is meant to establish. • A statement’s truth value is either true or false. o All statements have a truth value. A statement is false when what it says about the world is not actually the case. A statement is true when what it says about the world is actually the case. • A premise is a statement that is used in an argument to establish a conclusion.
What we can say about an argument: • An argument is valid if its premises necessarily lead to its conclusion. That is, if you accept that the premises are all true, you must accept that the conclusion is true. • An argument is sound if it is valid and you accept that all its premises are true. • A good, convincing argument is a sound argument. That is, since you accept all the premises are true, you must accept the conclusion is true (because the argument is valid). • A bad argument is any other kind of argument.
Examples: • “Every animal needs to breathe in order to live. Fish are animals. Fish cannot breathe in the air. Therefore, fish cannot live in the air.” Here, the claim is that “fish cannot live in the air.” The premises are “Every animal needs to breathe in order to live,” “Fish are animals,” and “Fish cannot breathe in the air.” The argument is valid – the premises necessarily lead to the conclusion. The argument is also sound – the premises are true. It is a good argument.
• “Oranges are green. All green things make me sick. Therefore, oranges make me sick.” The claim is “oranges make me sick.” The premises are “Oranges are green,” and “All green things make me sick.” The argument is valid – if we accept