Aenesidemus (ēnĕs'ĭdē`məs), Greek skeptic philosopher, fl. probably 1st cent. B.C. Thought to be a native of Knossos, Crete, he taught in Alexandria. Although his writings have been lost, it is known that his main contributions were 10 tropoi (ways to conduct arguments) that appeared in Pyrrhonian Discourses. His arguments, which point to the impossibility of knowledge, made him one of the leading skeptics.