In this article, it is proposed that processes of grammaticalization are determined and constrained not only by the source semantics of the grammaticalizing item, i.e. lexical persistence in the sense of Hopper (1991), but also by the original structure the item occurs in. This previously unrecognized feature of grammaticalization is referred to as structural persistence. The need to distinguish a structural equivalent to lexical persistence is argued on the basis of a particularly exemplary case, viz. the grammaticalization processes found with one lexically specific set of grammaticalizing elements in English, adjectives of difference such as other, different, various, etc. Before their grammaticalization, these adjectives occur in two different structural configurations, viz. (1) external comparison, in which the adjective describes a relation of difference between the referent of the noun phrase and a second, separately coded, entity, and (2) internal comparison, in which the entities that are said to be different are all denoted by the noun phrase containing the adjective. Even though they undergo the same general semantic process of grammaticalization and delexicalization in both structures, the adjectives acquire a different grammatical function in each of them. The different outcomes of the grammaticalization process can only be explained by relating them to the specific properties of the two source structures. © Cambridge University Press 2009.