 Consider first the often cited principle that says that substitution of synonyms is always meaning-preserving. As stated, the principle requires clarification. For one thing, not every case of replacement counts as substitution: the expression we replace with its synonym within a larger expression must be a constituent of the larger expression. Otherwise, as Geach pointed out, the synonymy of ‘Plato was bald’ with ‘Baldness was an attribute of Plato’ would guarantee the synonymy of ‘The philosopher whose most eminent pupil was Plato was bald’ and ‘The philosopher whose most eminent pupil was baldness was an attribute of Plato’; (Geach 1965: 110).