Instrument and Cause in the Indo-European languages and in Proto-Indo-European

While the semantic role instrument is uniformly encoded through the instrumental case (or cases that replaced it, such as the Latin ablative or the Greek dative) in ancient Indo-European (IE) languages, cause is variously encoded through plain cases or adpositional phrases. Comparison allows reconstructing a similar situation for Proto-Indo-European (PIE) as well. In particular, one can reconstruct cause expressions involving the plain instrumental, the plain ablative, and the adverb *pró, which, most likely, already had an adpositional function in the proto-language. It is assumed that cases and adverbs/adpositions originally had a spatial meaning, and that abstract meanings came about through metaphoric extension. In the case of the ablative and of *pró in cause expressions, some common patterns of semantic extension are visible (from source/origin to cause: the cause of a situation is conceived as its origin; from location to cause: a cause is conceived as an entity which constrains a situation by being placed in front of it). The instrumental case is traditionally thought as having originated as a comitative. While extension from comitative to instrument is based on the well-known ‘Companion metaphor’, an earlier local meaning of the PIE instrumental case cannot be reconstructed easily.