 It must be noticed that modern equational logic deals with universally quantified equations (which would have been called laws in the 1800s). In the 19th century algebra of logic one could translate “All \(X\) is \(Y\)” as the equation \(X = XY\). This is not to be viewed as the universally quantified expression \((\forall X)(\forall Y)(X = XY)\). \(X\) and \(Y\) are to be treated as constants (or schematic letters). Terms that only have constants (no variables) are called ground terms.