 These facts highlight the need for some criteria of the goodness of a pair \((\bK, \iEq)\) to provide a natural algebraic semantics for a logic \(\bL\) when some exists. One such criterion would be that \(\bL\) is an algebraizable logic with \((\bK, \iEq)\) as an algebraic semantics. Another that \(\bK\) is the natural class of algebras associated with the logic \(\bL\). The notion of the natural class of algebras of a logic system will be discussed in  Section 8  and the concept of algebraizable logic in  Section 9.