Critics cite weaknesses of Sankoff and Poplack's model. The free-morpheme and equivalence constraints are insufficiently restrictive, meaning there are numerous exceptions that occur. For example, the free morpheme constraint does not account for why switching is impossible between certain free morphemes. The sentence: "The students had "visto la película italiana"" ("The students had "seen the Italian movie"") does not occur in Spanish-English code-switching, yet the free-morpheme constraint would seem to posit that it can. The equivalence constraint would also rule out switches that occur commonly in languages, as when Hindi postpositional phrases are switched with English prepositional phrases like in the sentence: "John gave a book "ek larakii ko"" ("John gave a book "to a girl""). The phrase "ek larakii ko" is literally translated as "a girl to," making it ungrammatical in English, and yet this is a sentence that occurs in English-Hindi code-switching despite the requirements of the equivalence constraint. The Sankoff and Poplack model only identifies points at which switching is blocked, as opposed to explaining which constituents can be switched and why.