Halliday & Matthiessen (2014: 440):
Degree of interdependency is known technically as taxis; and the two different degrees of interdependency as parataxis (equal status) and hypotaxis (unequal status). Hypotaxis is the relation between a dependent element and its dominant, the element on which it is dependent. Contrasting with this is parataxis, which is the relation between two like elements of equal status, one initiating and the other continuing.