What are the things that we assert, believe, and desire? The orthodox view among philosophers is eternalism: these are contents that have their truth-values eternally. Transient Truths provides the first book-length exposition and defense of the opposing view, temporalism: these are contents that can change their truth-values along with changes in the world. Berit Brogaard argues that temporal contents are contents and propositions in the full sense. This project involves a thorough analysis of how we talk about and retain mental states over time, an examination of how the phenomenology of mental states bear on the content of mental states, an analysis of how we pass on information in temporally extended conversations, and a revival of a Priorian tense logic. The view suggests a broader view according to which some types of representation have a determinate truth-value only relative to features about the subject who does the representing. If this view is right, successful semantic representation requires an eye on our own position in the world.