We discuss sincere voting when voters have cardinal preferences over alternatives. We interpret sincerity as opposed to strategic voting, and thus define sincerity as the optimal behavior when conditions to vote strategically diminish. When voting mechanisms allow for only one message type (simple voting mechanisms) we show that eliminating some conditions for strategic voting, individuals' optimal behavior coincides with an intuitive and common definition of sincerity. In order to obtain a precise definition of sincerity in voting mechanisms allowing for multiple message types (complex voting mechanisms) further restrictions on strategic voting are required. We illustrate our methodological approach using approval voting (AV) as a prime example of complex voting mechanisms for which no conclusive definition of sincerity exists in the literature.Peer reviewed