 In addition, we need to separate two issues: whether substitution of synonyms can turn a meaningful expression into a meaningless one, and whether it can turn a meaningful expression into an expression with a different meaning. The principle that rules out the former possibility was first proposed by Husserl (1913: 318), and it is usually stated in terms of the notion of a semantic category. Two expressions belong to the same semantic category just in case they are intersubstitutable within any meaningful expression salva significatione (without loss of meaningfulness). According to Husserl’s principle: