The Art of Logic · Part 7 · Propositions · B2
Sentences and Propositions: True or False?
Part 7 of The Art of Logic: only a statement can be true or false. Questions, commands and wishes cannot. Logic works with propositions, and restates them as subject, copula and predicate. Sentence types and logical form (subject + is / are + complement), with Philo, Sophia, Marcos and Demetria.
Tonight, the unit logic really works with: the proposition.
Not quite. “Shut the door!” is a sentence. Is it true?
Exactly. A proposition is a sentence that is either true or false. Only statements qualify.
Sister Miriam Joseph, following Aristotle, defines a proposition as a sentence that asserts or denies something, and is therefore true or false. Questions, commands, wishes and exclamations express thoughts, but they assert nothing, so they are neither true nor false.
A simple proposition has three parts: a subject, a predicate, and a copula, the verb is or are that joins them. Logic restates sentences in this form: “Birds fly” becomes “Birds are creatures that fly”; “Socrates drank the hemlock” becomes “Socrates is a man who drank the hemlock.”
Grammar distinguishes simple sentences, complex ones (with a subordinate clause) and compound ones (two clauses joined by and, but, or). A compound sentence may contain two propositions, and each can be true or false separately.
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