Logic is the study of good reasoning, and reasoning is built from statements. Before we can weigh an argument, we need to know which sentences can be its parts. This is the first rung of the Logic Ladder, so we start from scratch.
Key idea
A statement is a sentence that is either true or false. Questions, commands, requests and exclamations are not statements, because they do not claim that anything is so.
Why it works
Reasons work by passing truth along: if these claims are true, that claim must be (or probably is) true too. Only a sentence that can be true or false can take part. "Please pass the salt" can be polite or rude, but never true or false, so it cannot be a reason for anything.
A statement does not have to be true. "Seven is an even number" is false, and it is still a statement. It also does not have to be a fact everyone agrees on. "Soccer is more fun than chess" is an opinion, but it claims something that people can agree or disagree with, so it counts.
Worked example: Statement or not?
Which of these are statements? (a) "Spiders have six legs." (b) "Bring your coat." (c) "It will rain tomorrow."
- (a) claims something about spiders. It is false (spiders have eight legs), but it is still a statement.
- (b) tells someone to act. It cannot be true or false, so it is not a statement.
- (c) is a prediction. We do not know yet whether it is true, but it will turn out true or false, so it is a statement.
Answer: (a) and (c) are statements; (b) is not.
Common mistake
Thinking a statement must be true, or that an opinion cannot be a statement. "Pizza is the best food" is a statement: it is simply one that people disagree about. Quick check: could someone sensibly reply "That's true" or "That's false"? If so, it is a statement.
A question can sometimes hint at a claim ("Isn't it cold in here?" hints "It is cold"). In this course we take sentences at face value: a question is not a statement.