All the X are Y but all Y are not X. What are X and Y?
X-Alkalis, Y-Bases
Bases exhibit certain characteristic properties such as -
They are usually metal oxides, metal hydroxides, metal carbonates or metal hydrogen carbonates.
Those bases that are soluble in water are known as alkalis. For example- NaOH, KOH. Therefore, all alkalis are bases but all bases are not alkalis.