Before revision:  We explore the extent to which diverse paraphrases can adequately cover the space of valid translations and compare to an alternative approach of generating paraphrases constrained by MT outputs. We compare both approaches to human-produced references in terms of diversity and the improvement in BLEU's correlation with human judgements of MT quality .
After revision:  We explore the extent to which diverse paraphrases can adequately cover the space of valid translations and thereby improve its correlation with human judgements of MT quality .