Halliday & Matthiessen (2014: 472):
Here one process is simply adjoined to another; there is no implication of any causal or temporal relationship between them. Additon falls into three subtypes — (a) ‘additive: positive’ (‘and’), (b) ‘additive: negative’ (‘nor’) and (c) ‘adversative’ (‘but’ — ‘and conversely’). Paratactic additions are often accompanied by cohesive expressions such as too, in addition, also, moreover, on the other hand.