Propositions form the basis for scientific research. The validity of a research study is, to a large extent, evaluated on the criteria of its propositions. For internal validity, study propositions provide information regarding precision of definitions, measurements, associations, confounding factors etc. that are considered in research. While for external validity, propositions form the premise for the deduction of inferences. The aim of this article is to help readers understand the propositions that are made in research. This article discusses those propositions, which are relevant to medical research.