On Friday, October 13th, Sally Thomason gave a keynote address, "Can Deliberate Language Changes Cause Problems for Quantitative Phylogenetic methods?", at the XLanS conference: Triggers of Language Change in the Language Sciences, in Lyon, France. After preliminary comments on two background topics -- how historical linguists establish genetic relationships and subgrouping models, and what kinds of contact-induced change are relevant to deliberate change -- she argued that most deliberate changes won't skew the results of either quantitative methods or traditional historical linguistic methods. Some deliberate changes, however, distort linguistic systems enough to hinder efforts to place a language in a family tree: the creation of secret languages may occasionally have this effect, and the creation of bilingual mixed languages will certainly do so. But such extreme results are, as far as we know, rare.