The document discusses propositions and hypotheses. It defines a proposition as a statement that predicts a relationship between two or more variables, while a hypothesis describes a proposition that will be tested. Propositions form the basis of scientific research and are used to evaluate a study's internal validity. The document provides examples of propositions and explains that a hypothesis predicts observations in empirical data and must be falsifiable. It must include a null hypothesis of no relationship and state an association but not causation. Supported hypotheses may become accepted theories over time if repeatedly tested and not falsified.