Logic simplifies and clarifies ordinary language and thereby improves communication by reducing or eliminating errors of interpretation. While English and other languages offer many ways of saying things, logic uses simple structures whose meanings are always clear because they are stated using only a few well-known forms. This chapter considers sentential logic in which every sentence may be either true or false but not both or of unknown truth value. Such logic simplifies communication from the uncertainty that is common in ordinary language. Negation, conjunction, disjunction and implication (or conditionals) are illustrated by truth tables. All are valuable in theory development and enable the prediction of outcomes from premises.