University of California, San Diego: Edward Bender and S. Williamson's "Arithmetic, Logic, and Numbers: Logic"
Study definition 1 (Tautology, contradiction) in Section 1 on pages Lo-2 and Lo-3. In Subunit 1.1.2 of this course, we introduced translation between English statements and logic. This reading, in addition to tautology and contradiction, adds to the translation story by discussing the relationship with set theory. Thus, you can translate from and to English, logic, and set symbols. The discussion of translation will continue when you study implication in the Subunit 1.2.1.