Any given semienclosed basin may change from vertically homogeneous to strongly stratified in one tidal cycle. These stratification changes can occur at various temporal scales and that is why it may sometimes be irrelevant to classify a basin with these guidelines unless we specify the gamut of variability and its temporal scales. A basin typically changes geomorphology over hundreds to thousands of years and its classification will likely remain the same in our lifetime. However, a basin may change water balances in monthly to seasonal scales and vertical stratification in even shorter periods. Because of this variability, we should be cautious when trying to classify any semienclosed basin. Other robust approaches to classifying these basins are presented in Chapter 12, which includes a dynamical approach. So, before understanding such a dynamical approach, we need to familiarize ourselves with the fundamentals of the dynamics of semienclosed basins. This acquaintance is formulated in Chapters 2 to 11.