Aenesidemus was a philosopher of the school of skepticism.

He was born at Gnossus in Crete, but lived at Alexandria and flourished shortly after Cicero.

Aenesidemus revived the skepticism which had been silenced in the Academy, with the view of making it assist in reintroducing the doctrines of Heraclitus. For, in order to show that everything has its  contrary, we must first prove that opposite appearances are  presented in one and the same thing to each individual. To strengthen the cause of skepticism, he pushed its limits and defended the ten tropes or modes of skepticism – techniques or arguments to show that judgement must be withheld on any issue.

Although Diogenes  Laertius attributes the ten modes to Pyrrho, it is likely that they owe their exisytence to Aenesidemus.

Extracts of the ten modes are found in Photius (cos.212).

Briefly, the modes are as follows:

     1. The feelings and perceptions of all living beings differ.

     2. People have physical and mental differences, which make things appear     different to them.

     3. The different sesnses give different impressions of things.

     4.   Our perceptions depend on our physical and intellectual  conditions 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. For example, we see things through the air.

7.      Things appear different according to variations in their quantity, color, motion, and temperature

8.      A thing impresses us differently when it is  familiar and when it is  unfamiliar

9.      All supposed knowledge is predication. All predicates give us only the relation of things or to ourselves; they never tell us what the thing  in itself is.

10.  The opinions and customs of people are different in different countries.