In present-day discussions on the practice of animal vivisection, it is normal to consider Descartes as an advocate of this practice, as a result of his dualistic philosophy. Some of the sources say that Descartes denied the animals could feel pain, and therefore could be used without concern.[45] Other sources consider that Descartes denied that animals had reason or intelligence, but did not lack sensations or perceptions, but these could be explained mechanistically.