donkey sentence
Definition - A sentence that is well-formed but which defies attempts to generate its formal symbolic-language equivalent, e.g. Every farmer who owns a donkey beats it.

1. In the example, the word it is a donkey pronoun.

Example Usages -

1. "There is, for example, no Piraha╦ť equivalent to a “donkey sentence” (“Everyone who owns a donkey beats it”)."
(Source: Cultural Constraints on Grammar and Cognition in Pirahã: Another Look at the Design Features of Human Language. Everett, Daniel L. Current Anthropology, Vol 46(4), Aug-Oct 2005, 621-634. (Pg 628) )

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