Rule independence and rule conditioning: Grammar competition in Old English relative clauses

Grammar competition usually involves structured variation with two variants. However, it is also possible that two competing rules do not involve the same initial node in a syntactic tree, but merely make a similar functional contribution. For such cases, it is possible to find diachronic variation with three variants - two for each separate rule and one for the two rules combined. It is argued that a necessary condition for the existence of overlapping forms is rule independence, i.e. the absence of conditioning factors. Old English relative clauses are analysed as an instance of grammar competition with three variants to substantiate this claim.