There is no consensus about what exact type of literature slave narratives are, whether they can be considered as a proper genre, comprised in the large category captivity narrative, or are autobiographies, memoirs, testimonials, or novels; nonetheless, they play a big part in keeping up the memory of slavery and in approaching a topic that was considered as a taboo for a long time - especially since many denied and still deny the existence of slavery. Given the participation in the 19th century of abolitionist editors (at least in the United States), influential early 20th-century historians, such as Ulrich B. Phillips in 1929, suggested that, as a class, "their authenticity was doubtful". These doubts have been criticized following better academic research of these narratives, since the late 20th century historians have more often validated the accounts of slaves about their own experiences.