Greek Philosopher Aenesidemus

Aenesidemus was a Greek philosopher of the 1st century B.C. Born at Knossos, Crete, he taught skepticism in Alexandria, Egypt. His writings, which are lost, included Kata sophias (Against Wisdom), Peri zeteseos (On Inquiry), and Prote eisagoge (First Introduction).

Ten well-known arguments asserting the impossibility of knowledge are attributed to Aenesidemus. These arguments, called tropoi tes epoches (tropes of suspense of judgment), contain only a few distinct ideas, since some of them express the same thought in different ways.

They are: (1) sensations and perceptions differ; (2) mental and physical differences among individuals make things appear differently to them; (3) different senses produce different impressions; (4) perceptions depend upon an individual's mental and physical condition at the time of perception; (5) things appear different in different positions and at different distances; (6) perception is never direct, but always through a medium; (7) things appear different according to variations in their color, motion, quantity, and temperature; (8) degrees of familiarity cause differences in perception; (9) all supposed knowledge is based on predication; and (10) opinions and customs differ in different countries.