Full Idea
A 'unigrade' relation R has a definite degree or adicity: R is binary, or ternary....or n-ary (for some unique n). By contrast a relation is 'multigrade' if it fails to be unigrade. Causation appears to be multigrade.
Gist of Idea
'Multigrade' relations are those lacking a fixed number of relata
Source
Fraser MacBride (Relations [2016], 1)
Book Reference
'Stanford Online Encyclopaedia of Philosophy', ed/tr. Stanford University [plato.stanford.edu], p.2
A Reaction
He also cites entailment, which may have any number of premises.