Here we can, however, also say : 'The laughing-capable Socrates', suggesting now (like in the case of the difference) a necessary unity, because instead of 'the rational Socrates' we can also say : 'the (discursively) thinking-capable Socrates'.
'Man' directly stands for the (human) dynamical law, the genotypic domain.
'Rational' here stands (that is, it is here so meant) directly for a part of the dynamical law, and thus also refers to the genotypic domain.
'capable of laughing' ( = ability to laugh), however, stands for a determination, here a proprium, and thus refers to the phenotypic domain. In this way the necessary twoness appears.