 Some philosophers argue that only the latter, eternally true kind of proposition could make sense of how we use propositions to reason over time. We need propositions to have stable truth values if we are to use them as the contents of thoughts and communication. Other philosophers—particularly those who believe that reality itself changes over time—think that tensed propositions are needed to accurately reason about the world. We’ll return to these issues in  Section 4  and  Section 5.