Grammaticalisation, the historical emergence of new items with grammatical function from earlier lexical items, is generally considered to be a unidirectional process. Much recent interest has, however, focused on degrammaticalisation changes that run counter to this general direction. This paper considers three cases of degrammaticalisation from Bulgarian and Welsh, involving shifts from pronoun to noun, and from preposition to verb. These cases exhibit a common set of properties, such as the central role played by syntactic reanalysis and pragmatic inferencing, that justify viewing them as examples of a new type of degrammaticalisation. Degrammaticalisation via syntactic reanalysis appears to be cross-linguistically rare, because it is constrained by two factors: the requirement that the item in question should have become grammatically or semantically isolated, and the requirement that it should match the phonological and morphological patterns of the lexical category.