This study examines the meaning of prototypical conditional-sentence markers like English if and Spanish si from a primarily pragmatic perspective. It argues that the sense of "hypotheticality" often associated with the encoded semantics of such markers is actually a pragmatic conversational implicature that is cancelable in certain discourse contexts. The analysis therefore redraws in radical fashion the semantics-pragmatics boundary as it applies to the meaning of conditional markers.A number of key implications are presented in detail. First, it is shown that "factual" if-clauses, typically considered anomalous despite their frequent occurrence in many types of discourse, fall out from the predictions made by the pragmatic view of conditional marker meaning. Second, it is demonstrated that the "hypotheticality" implicature interacts with the well-known implicature of conditional perfection, and that this interaction allows one to predict when "biconditional" readings of simple conditionals will and will not arise. More generally, the model of meaning developed in this book permits clear links to be made between conditionality and other conceptual domains, such as adversativity and scalarity. These links are examined in chapters 4 and 5 using declarative-sentence uses of Spanish si as the empirical testing ground.This book will be of interest to linguists working in semantics and pragmatics, discourse analysis, and Hispanic linguistics. It will also appeal to scholars interested in the interface between communication and cognition.