 Fonseca engages particularly with the rejection of haecceities in the Thomist Cajetan (most notably in Cajetan’s commentary on Aquinas’s De ente, c. 2, q. 5, nn. 33–36 (Cajetan [CBE], 94–98)). Cajetan worries that haecceities need to be in some sense similar to each other – and specifically that the haecceities of Socrates and Plato must be more similar than the haecceities of Plato and some white patch (Cajetan, In de ente, c. 2, q. 5, n. 36 (Cajetan [CBE], 97); see Fonseca, In Met. V, c. 6, q. 5, sect. 2 [Fonseca (1599), vol. 2, col. 185C-D]). According to Fonseca, haecceities are similar to each other without having anything real in common: they are thus primarily diverse in the required sense, even though the haecceities of Socrates and Plato are more similar than the haecceities of Plato and some white patch (Fonseca, In Met. V, c. 6, q. 5, sect. 2 [Fonseca (1599), vol. 2, col. 185E-F]). More generally, Fonseca (rightly) holds that exact similarity between two haecceities would entail that the two haecceities were numerically identical (Fonseca, In Met. V, c. 6, q. 5, sect. 2 [Fonseca (1599), vol. 2, col. 185B]).