Paraphrasing with Bilingual Parallel Corpora 
 Previous work has used monolingual parallel corpora to extract and generate paraphrases . We show that this task can be done using bilingual parallel corpora , a much more commonly available resource . Using alignment techniques from phrase-based statistical machine translation , we show how paraphrases in one language can be identified using a phrase in another language as a pivot. We define a paraphrase probability that allows paraphrases extracted from a bilingual parallel corpus to be ranked using translation probabilities , and show how it can be refined to take contextual information into account. We evaluate our paraphrase extraction and ranking methods using a set of manual word alignments , and contrast the quality with paraphrases extracted from automatic alignments . 