Agnosticism, ag nos'ti sizm, the doctrine that the existence of a personal God or an unseen world can not be proved or disproved. Those holding this doctrine also maintain that one can not prove his own existence. Agnosticism is founded on the inability of the human mind to arrive at absolute knowledge and belief and the failure of scientific investigation to discover the first causes for the phenomena of nature. An ancient form of agnosticism is found in the doctrine of a school of philosophers known as the Sophists.